Structure , Pha se B ehavio r, Molecula r Dyna mics and Co nductivi ty
of Colu mnar Liq uid Crystals in th e Bul k State and Under
Confinemen t

Vorge le gt von
M.Sc.
Ard a Yild irim

von d er Fa kultä t II - Ins titut f ür C hem ie
der Technis che n Unive rsit ät Be rlin
zu r Erla ngung des akad emisc hen Grades
Dok tor der In genie urwis sensc haf ten
(Dr. – Ing.)

ge nehm igte Dis serta tion

Prom oti onsaus sch uss:
Vor sitz end er: P rof. Dr . Matt hias Bic kerm ann
Gutac hter : Prof . Dr. Mic hael G radzie lsk i
Gut acht er: P ro f. Dr. Regine von Klit zing (TU Dar mstad t )
Gutac hter : Prof . Dr. Andre as Sc hönha ls (B AM)

Tag de r wis sensc haf tlich en A usspra che: 20. 12 .2019

Ber lin 20 20

“ For e very thing in the wor ld – for c ivil izatio n, for life, for s ucce ss – the tr uest gui de
is k nowle dge an d sci ence. T o see k a gui de ot her th an kn owle dge a nd scie nce is
unaw aren ess, ign oranc e and m isgu ided ness. ”
Mus tafa Kem a l Atatür k, 192 4

i

ABSTRACT
Mol ecules of c olumnar liqu id crysta ls ( C LC s ) ty p ica lly consistin g of a r i gid arom ati c core an d
flexible a l k yl chains , can form a colu mnar m esoph as e b y self - assem bl y . Th is self - assemb l y of t he
mol ecules in t he col um ns are drive n b y π - π interactions am ong the ar om ati c cores, while th e a lk y l
cha ins fill the intercolum nar space. Among other promising features of CLCs for a ppl ications, the
chara cteri sti c one- dimens ional (1D) cha r ge t ransport featu re , due to π - orbitals with de localized
electro ns, qualifie s C LCs for vari et y of electronic a pplication .
In t h is wor k, select ed differ ent columnar liquid c r ystals ( C L C s) were s y stem atica ll y s tudied in
order t o eluci dat e the ir structure, phase behavior, m olecular dynamics and conductivit y . I t is aimed
to gain a n underst anding of the struc t ure - d y namics -propert y relationship s of the CL C s . T he
s ys t e m s cho sen in this study corresponds t o hex akis (n - alk y lox y) triphen y lene - based discotic liquid
crysta l s (DLCs) , whic h a re extensively studied model sy stems and cons id er ed as “worki n g ho rse”
of the C LC research . In addition to the selected triphen y l ene - based CLCs, dipole -functionalized
C LC s relat e d to these sel ected CLCs and columnar ionic liqui d cr ystals (ILC s) wer e chosen due
to the interest of both scientific and application points of view.
The research work is foc used on two diff erent states of columna r liquid cry stalline syste ms ,
which are “C LCs in the bulk state” and “a CLC under na noconfin ement” . On the one hand, for the
investigations of CL Cs in the bulk state , unfunctiona l ized as w ell as mon o -dipole-func t ionalized
triphe n y len e - based DL Cs , triphen y lene crown ether - based D LCs and columnar I LC s w e re studied.
On the other hand, f or th e investigations of a CLC under nanoconfine m en t , an unfunctionalized
triphe n y len e - based DLC confined into c ylindrical nanopores was investi gated. All CLCs studied
in this work form a hexag on al column ar (Co l h ) m esophase. The ma in ex perim ental tech niq ues

ii

applie d for this study a re differe ntial scanning calor imetr y (DSC), broadband dielectric
spect rosco p y (BD S), s pecific h eat spe ctro sco p y (SHS ) emp lo y i n g dif ferenti al AC -chip
calori met r y and te mperature modulate d DSC (TMDSC), as we ll as fast scanning calor imetr y
(FSC). In addition, differe nt complementar y t echniques were also used, includin g
thermogravimetric a n al ysis (TGA) , Fourier transform infrared spectroscopy (FTIR), polar i zing
optica l mi cros cop y (PO M), and X- ra y d iffraction (XRD).
I n the first part of the thesis reg a rding the investigations on the dif ferent CLC s in the bulk s tate ,
t he mesomorphic prope rt ies of the CL C s were exp lored using POM and XRD . The POM and XR D
inv esti gation s evi den ced th e cha ract eris ti c mesomorphic properties of the Col h mesophase s
formed. M oreov er, an amorphous halo in the XRD pattern was observ ed for all sy stems studie d ,
which indicat es nanophase separation between the substituents filling the i ntercolumnar area and
the columns formed by the cores. T he pha s e behavior of the CLCs was explored conducting
conventional DSC mea surem ents . The phase transition temperatures and enthalpies we re
determined. Th e D S C investig ations showed tha t all C L C s studied , ex cept on e of t he mat erial s ,
have a pla stic crysta lline ( C r y) phase, a Col h mesop hase and an isotropic (Is o) phase upon heating
from 173 K. Furthermore, a t lea st one ther mal glass tr ansition was detect ed by DSC for all CLCs .
For the triphe n y l ene- b a s e d D LC s , two differ ent thermal gla ss transitions were found.
The mo lecul ar d y nam ics tak ing pl ace i n t hese s yst ems as well as t he cond ucti vit y w er e prob ed
using BDS in a broad frequenc y and temp erature range. Additionall y , t he glass y d y namics were
studied using advanced calorimetric techniques; SHS and FSC . H ence, a n understanding of th e
mol ecular d ynam ics w as obt ained from differe nt pers pecti ves . The i nves tigati ons reve aled a
γ - process and α - p ro cess es (multiple glassy d ynamics ) for a l l C L Cs st udied in this work. The
γ - processe s probed by BDS are ass igned t o th e PE - like lo caliz ed fluctuations of the meth y l groups

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of the alk y l chains f illing the inte rcolumnar a rea . Among the multiple glas s y d ynam ics detect ed
( α 1 -, α 2 -, α 3 - and α 4 - processes) , t he α 1 - pro cess es ob serv ed for al l C LCs a re attributed to th e PE - like
coopera t ive fluctuations t aking place in the alk yl c hai ns . Moreover, other glass d y namics ( α 2 -, α 3 -
and α 4 - processes) de t ected b y BDS are ambiguousl y attributed to the cooperative fluctua t ions of
the co res. Different possibilitie s of the molec ular assi gnme nt of these glassy dy namics are
proposed and fur ther disc ussed in the thesis. I n addition to th e relaxation processes, a conductivit y
contribution was observed b y BDS fo r al l C LCs . I n order to qua nt if y the conductivit y contribution
as well as t o reveal the co ndu ctiv it y mech anis m, the conductivit y contributi on was anal yzed in
deta il and discussed.
In the second part of the t hesis regarding the inve s tigations on a C LC unde r nanoconfinement,
a t riphen y lene - based D LC confined into c y lindri cal nanopores of anodic aluminum oxide and
sil ica m embran es , having pore sizes from 161 nm down to 12 nm , was stud ied .
n-O ctcy lp hosphonic acid ( OPA ) and n- octad ecylphosphonic acid ( ODPA ) modific ations wer e
used t o gra ft the h y drophilic inner walls of the por es with alk y l chains, consequently, the
hydrophobic pore w al ls wer e obt ain ed. The study considers both unmodified and modified pore
walls. T he phase behavior under the nanoconf i nement w as ex plored using DSC. Th e DSC
investig ations elucid ated the pore size dependenc i es of the phase tr ansit ion temperatures a nd
enth alpi es. Th e coll ecti ve orientational order (dominating molecular ordering) under the
confinement was probed using BDS. The molecular orde rin g under the nanoconf i nement was
deduced to be pore size and surface chemistry dependent. Th e r esults ev iden ced that the
dominating planar axial c onfiguration, onl y c on fi guration suitable for electronic applications, was
succes sful l y ac hieved b y both OPA- and ODPA -modi fications for most of the pore si zes probed.

iv

ZUSAMME NFASSUN G
Moleküle von kolumnaren Flüssigkristallen (CLCs), die t y pis cherweise aus einem starren
aromatischen Kern und flexiblen Alk y l ketten best ehen, können durch Selbstorganisation eine
kolumnaren Mesophase bil den. Die S elbstorganisation der Moleküle in de n S äulen wird dur ch π -
π - I nte raktionen zwischen den aromatischen Kernen bewirkt, wä h rend di e Alkylke t ten, die den
zwischenkolumnaren Raum füllen. Neben anderen vielversprechenden Anwendungsmöglichkeit
von CLCs qualifiziert die charakteristische ei ndimensionale (1D) Ladungstransportfunktion
aufgrund von π - Orbitalen mit delokalisierten Elektronen die CLCs für eine Vielzahl von
elektronischen A n wendungen.
In die s er Arbeit wurden ausgewählte verschiedene kolumnare F lüss igkristalle (CLCs)
systematisch untersucht, um ihre Struktur, ihr Phasenverhalten, ihre Molekulard y n amik und ihr e
Le i tfähi gkeit zu verstehen. Zie l ist es, ein Ve rständnis der strukturdyna m isch en
Eigenschaftsbe z iehungen der C LCs zu gewinnen. Die in dieser St udie ausgewählten S y s teme
ents prech en hex ak is (n - alk yloxy) t riphen y l enbasierten diskotischen Flüssigkrist allen (DLCs), die
umfassend untersuc ht e Modells y st eme sind und als "Ar beitspfe rd" der CL C- F o rs chun g gelten .
Zusä t zlich zu den a usgewählten triphenylenbasierten CLCs wurden aufgr und des
wissenschaftliche n und a nwendungsbezogenen Interesses dipolfunktionalisierte CLCs in Bezug
auf diese ausgewählten CLCs und kolumnare ioni sche Flüssi gkristalle (ILCs ) aus gewäh lt .
Die Forsc hun gsarbeiten konzentrieren sich auf zwei verschiedene Zustände kolumnarer
flüssigkristalliner Sy st eme, den "CL C s im Volumentzustand" und "ein CL C unt er
Nanoconfine m ent". Zum einen wurden für die Untersuchung von CL C s im Volum e ntzustand
sowohl unfunktionalisierte als auch mono Dipol funktionalisierte tripheny l enbasierte DLCs,

v

triphenyle nk ronenetherbasierte DLCs und kolum nare ILCs ausgewertet. Andererseits wurde für
die Untersuchunge n eines C L C unter Nanoco nfinement ein unfunktio nalis iert es D LC auf
Triphen y l enbasis untersucht, das in z y lindrischen Nanoporen e in geschlossen werde. Alle CL Cs,
die in dieser Arbe it untersucht wurde n, bi lden eine hexagonal geordnete flüssig kristalli ne
Meso phase. Di e wi chti gs ten ex peri ment ell en Te ch nik en , die für diese S tudie verwendet werden,
sind die D ifferentia l -S canning- Kalorimetrie (DSC), die dielektrische Breitbandspektroskopie
(B DS), die spezifisc he Wärmespe ktroskopie (SHS) mit differe ntieller AC -Chip- Kalorime trie und
die te mperaturmo dulierte DSC ( TMDS C) so wie die Fasts can - Kalorimetrie (FSC). Darüber hina us
wurden auch unterschiedliche komplementä re Techniken eingesetzt , darunter die
thermogravimetrische Analyse (TGA), die Fourier -Transformations- Inf r arotspektroskopie
(FTIR), die optische Polarisationsmikrokopie (POM) und die Röntgendiffraktion (XRD).
Im erst en Tei l de r Arb ei t d er Unt ersu chu n gen an den versch i edenen C LCs im Mass enz ust and
wurden die mesomorphen Eigenschaften der CLCs mit P OM und XRD studiert. Die POM - und
XRD - Untersuchungen zeigten die charakteristischen mesomorphen Eigens chaften der gebildeten
hexagonal ge o rdnete flüssigkristalline Mesophase. Darüber hinaus wurde ein amorpher Halo gen
im XRD - Spektrum für alle untersuchten Sy stem e beobachtet, wa s auf eine N anophas entrennung
zwi schen den S ubstituenten, die den interkolumnaren Bereich ausfüllen, und den von den Kernen
ge bi ldeten Säulen hin weist. Das Phasenv erhalten der CLCs wurde weiter durch konventionelle
DSC - Messungen untersucht. Die Phasenübe r gangstemperaturen und Enthalpien wurden
bes timmt. Die DSC - Unt ersuchungen zeigten, dass alle untersuchten CL C s, m it Ausnahme eines
der M aterialie n, eine pla s tisch krista lline (Cry ) -Ph ase, eine he x agonal geordnete flüssigkristalline
Mesophase und eine i sotrope (Iso) - Phase beim Erwärmen von 173 K zu h o hen Tem per atu ren
aufweis en. A uß erdem wu rde mi ndes ten s ein therm is cher Glas über gan g mi ttels DS C für al le C LCs

vi

nach gewi esen. Für d ie tri phen ylenb asi erten D LC s wu rden z wei u nter schi edli che th ermi sch e
Glasübergä n ge gefunden.
Die in d iesen Sy stemen stattfind ende Moleku lardynamik so wie die Le itfähigkeit w urde n mit
BDS in einem brei ten Frequ en z - und Temperaturbereich untersucht. Zusätzlich wurde die
glasartige Dynamik mit modernen kalorimetrischen Techniken wie SHS und FSC untersu cht.
Daher wu rd e ei n Vers t ändni s d er mol ekul are n D y n am ik aus v ersch ied enen P ersp ekt iv en
gewonnen. Die Untersu chungen zeigten einen γ - Prozess und α - Pr oz esse (multiple glasa rti ge
Dynamik) für alle in dieser Arbeit unt ersuchten C LCs. Die von BDS unters uchten γ - Prozesse sind
den PE - ähnli chen lokalis ierten Fluktuationen der interkolumnaren Bereich füllenden Alk ylketten
zuge ordnet. Di e mu ltiple g lasartige D y namik (α 1 - , α 2 - , α 3 - und α 4 - Pro zes se) werd en für all e C LCs
beobach tet en α 1 - Proz esse dem PE zugeschrieben, wie kooperative Schwankungen in de n
Alk ylkett en. Darüb er hi n aus werd en and er e du rch BDS na ch gewies ene Glasd ynam iken (α 2 - , α 3 -
und α 4 - Prozesse) mehrdeutig auf die kooperativen Fluktuationen d er Kerne z ugeordnet.
Verschie d ene Möglichkeiten der molekularen Z u ordnung dieser g l asarti gen Dy n amik werd en
vorgeschlagen und in der Arbeit weiter diskutiert. Zusätzlich zu den Relaxationsprozessen wurde
durc h die BDS ein Le it fähigke itsbeitrag für alle CL Cs beobachte t. Um den Leitf ähi gke itsbeitrag
zu quantifizieren und den L eitfähigkeitsmechanismus aufzuzeigen, wurde der
Le itfähi gke itsbeitrag d et ailliert a nal y siert und diskutie rt.
Im zweiten Te il der Arbeit wurde ein DL C auf Triphen y l enbasis untersucht, das in
z y lindrischen Nanoporen von anodischen Al umini umoxid - und Silica - Me mbranen mit
Porengrößen von 161 nm bis 12 nm eingeschlossen wurde. n -Octc y lphos phonsäure- (OPA) u n d
n- Octadecylphosphonsäure (ODPA) - Modifikationen wurden verwendet, um die h y d rophilen
Innenwände der P oren mit Alk y lketten zu h y d rophobi eren. Die Studie betrachtet sowohl

vii

unveränderte a l s auch m odifiz ierte Porenwände. Das Phasenverhalten unter der Nanoconfinement
wurde mit Hilfe von DSC untersucht. Die DSC - Untersuchunge n erhellten die
Porengrößena bh än gigkeiten der Phasenübergangstemperature n und Enthalpien. Die kollektive
Orientierungsordn ung ( d omini erende m olekulare Ordnung) unter Confinement wurde mit Hilfe
von BDS untersucht. Die m olekulare Or dnun g unter dem Na noconfin ement ist abhäng ig von der
Porengröße und de r Ob erflächenchemie. Die Ergebnisse zeigten, dass die dominierende planare
ax iale Konfig u ration, die nur für elektronisch e Anwendungen geeignet ist, erfolgreich durch OPA -
und ODPA-Modifikationen für die m eisten der untersuchten Porengrößen erreicht wurde.

viii

ACKNOWLE DG MENTS
First and foremost, I woul d like to express m y deep gratitude to Prof. Dr. Andreas Schönhals
for providing m e the opp ortunity to carry out my Ph.D. work on this fascinating topic and to be a
part of his rese arch group in Bundesanstalt für Materialforschung und - prüfun g ( BAM ) . In a ddit ion
to his precious guidance and support, he has alwa y s b een an exemplar y sc i entist and person to me
in these four year s with bot h his academic and personal attitude and val ues. Throughout this
demanding journey, it has alwa ys been a comfort t o feel his guidance, support, enc ou ragement and
patience, tha nks so whic h today I became not onl y a mor e equipped scientist but also a better
person. I would also like to ac knowled ge the financial support from the German Science
Foundation DFG for SC HO -470/20-1.
Moreover, I would like to pres ent m y s in cer e app reci ati on t o Pro f. Pat rick Hu ber and Kathrin
Sent ker from Hamburg University of Technology as well as to Prof. Dr. Sabi ne Laschat and
Andrea B ühlme yer f rom the Univer sit y of Stuttg art for their va luabl e contributions in this
collabora tive res ear ch w ork with them as well as their continuous support, understanding and
valuable suggestions. Thanks to their c ont ributions, this project was br oadened the re se arch
possibilitie s including n e w liquid cry stal line systems an d di ffer ent ex peri ment al t echni ques , an d
therefo re this project has flourished. I also announce the German S cience Foundation DFG for
financial support for HU 850/5 - 1 and LA 907/17 -1. Furt herm ore , I want to thank Dr. Mi chael
Gra dz ielski (T U Berlin) a nd Prof. Dr. Regine von Klit z ing ( TU Darmstadt) for taking over the
duty to review my t hesis. I n addition, I also would like to thank Dr. Jürgen E. K. Schawe for the
experimental help and fruitful discussions about FSC.
I w oul d like to thank all co lleagu es i n BAM who kindl y contributed to this work. First, I thank
Prof. Dr. Heinz Sturm (BAM) for the guidance, help and support. Dr. Glen J acob S mal es and D r.

ix

Brian R ich ard P auw are t hanked for enabli n g SAX S ex perim ent s , Dietmar Neuber t fo r his he lp in
the DS C m easur ement s, S igri d Benemann for the SEM im age s, Dr. J ana Falke nha gen for the
M A LD I - TO F me asu rem ent s and C hri st iane W eim ann fo r he r ass ist anc e in P OM measu rement s. I
also want to thank S e r ge j Petrov and Fra nk Milczewski for the ir help with the daily pr oblems faced
in the la b. Mohamed Aejaz Kolmangadi as a M. Sc. student working in t his presented work, is
sincerely thanke d due to his considerable contributions for the studies on columnar ionic liquid
cr ystals an d tri phen y l en e crown et he r - based disc o tic liquid cry stals.
I al s o would like to express m y thankfuln ess to all m y colleagues in m y group in BAM, D r.
Sheri f M adkour, M. Sc. Paulina Sz y moniak, M. S c. Marcel G awek , Dr. Shereen Omar a, D r. Huaj ie
Yin, Dr. Anna M aria E lert , Dr. Ievgeniia Topolniak, Maximilian Ebisch, Kor inna Alt mann,
Caroline Goedecke, a nd Dr. Nora Konnertz not onl y for all scientific support but also for the
countless memories and joy . Especiall y th anks to Dr. Sherif Madkour a nd M .Sc. Paulina
Sz y moniak, this almost four y e ars of m y research work at BAM was great p leasu re an d jo y wi th
them desp ite t he challenges, struggles and frustrations I h a d durin g m y P h.D. work.
At t he end , I would like to t hank m y friends ar ound the world for their love and support
throughout my y ears of stud ying. Am ong them , I need to add specials thanks to Dr. Ö zgün Attila ,
Görkem Özmen, M.Sc. Onur Do ğ u and Ö zkan Öznar for their co untless support and
encouragement to move forward as well as their p riceles s fri ends hip . Also, I want to thank m y
Be rlin Family – Ne ş e Çakmak Görür, Ca n Görür, Elif Eryilmaz Sigwa rth a nd Vincent Sigwar t h –
for providing m e the warmth of a fa m il y in Berlin and the i r incorpore al sup port. Most importantly ,
I would like to thank m y lovel y g irlfriend , Me ri ç Benderlio ğ lu , so mu ch fo r h er en dles s pat ien ce,
being th ere in the good time a nd (especia ll y ) in the bad times , the cou ntl ess s acrific es sh e h as made
and her endless perseverance. She has not onl y pati ent l y support ed me to ach ieve m y go als but

x

also brought me so muc h happiness and love . She h as been the sou rce of m y motivation and
streng t h. Finally, I would like t o ex press m y s incere thankfulness and gratitude to m y parents, Neşe
and Nadir Yıldırım, as well as my brother Tolg a Yıldırım for their comple te trust and support not
only throughout m y Ph. D. stud y but also throughout m y whole life. Th e sent enc es t hat I can
establish for m y famil y whether written or verbal, are not enough to describe my feelin gs – full of
love and g r atitude – towards them. Accomplishment of this work and wher e I am today, is the
result of their constant love, patience, trust, and encourage m ent throu ghout my e nti re life.

To M y Pa rents an d Meri ç Bend erl ioğlu

I

TABLE OF CONTENTS
CH AP T E R 1 – INTR OD UCTI ON ........................................................................................................................ 1
CH AP T E R 2 – BACKGRO UND .......................................................................................................................... 6
2.1 . Colum na r Liquid Crysta ls .................................................................................................................... 6
2.1.1. Disc otic Liq uid Cr ysta ls ................................................................................................................ 9
2.1.2. Discotic Liquid Crystals Un de r Nanoscale Confin ement .......................................................... 13
2.1.2 . Ionic Liquid Crystals .................................................................................................................. 15
2.2. Glass Transition and Gl ass y Dynamics ............................................................................................. 16
2.2.1. Glass T ransition ........................................................................................................................ 16
2.2.2. Glassy Dyna mics ....................................................................................................................... 19
CH AP T E R 3 – EXPERI MENTAL TECH NIQUES ............................................................................................... 23
3.1. Principles of Main Experimental Techniques .................................................................................. 24
3.1.1. Bro adband Dielectric Spectroscopy ......................................................................................... 25
3.1.2. Specific Heat Spectr oscopy ...................................................................................................... 33
3.2 Exp erimental Section ........................................................................................................................ 35
3.2.1. The rmogravi m etric Analysis ..................................................................................................... 35
3.2.2. Fourier Transform Infrared Sp e ctroscopy ................................................................................ 36
3.2.3. Differential Scanning Calo rimetry ............................................................................................ 36
3.3.4. Polarizing Optical Microscopy .................................................................................................. 36
3.3.5 . X - ray Scattering ........................................................................................................................ 37
3.3.6. Bro adband Dielectric Spectroscopy ......................................................................................... 39
3.3.7. Specific Heat Spe ctroscopy ...................................................................................................... 41
3.3.8. Fast Scanning Cal orimetry ........................................................................................................ 44
3.3. Mat erials .......................................................................................................................................... 45
3.3 .1. T riphe nylene - Based Discotic Liquid Crystals ............................................................................ 45
3.3 .2. T riphe nylene C rown Et her - Based Discotic Liquid Cryst als ....................................................... 47
3.3.1. Columnar Ionic Liqui d Cry stals ................................................................................................ . 48
3.4. Preparation of the Sa mples for the Investigation o f a CL C under C onfinement ............................. 49
3.4.1 Confining Hosts .......................................................................................................................... 49
3.4.2. Surface Modificati o n of the Confining Hosts ........................................................................... 51
3.4.3. Pore Filling Procedure .............................................................................................................. 53
CH AP T E R 4 – COLU MNAR L IQUID C RYSTALS IN THE BU LK STATE .............................................................. 54

II

4.1 . Tri phenyle ne - Based Di sco tic Liquid Crystals ................................................................................... 54
4.1.1. M esomorphic Properties .......................................................................................................... 55
4.1.2. Phase Behavio r ................................................................................................................... 58
4.1.3. M olecular M obili ty ............................................................................................................ 61
4.1 .4. C onc lusions ............................................................................................................................... 72
4.2 . Tri phenyle ne Crown Ether - Based Dis cotic Liquid Crystals .............................................................. 74
4.2.1 . Phase Behavior ......................................................................................................................... 75
4.2.2. Mole cular Mobility ................................................................................................................... 77
4.2 .3. C onduc tivity .............................................................................................................................. 83
4.2.4 . Conclus io n ................................................................................................................................ 85
4.3. Ionic Liquid Crystals ......................................................................................................................... 87
4.3.1 . Phase Behavior ......................................................................................................................... 88
4.3.2. Mole cular Mobility ................................................................................................................... 90
4.3.3 . Conducti vit y .......................................................................................................................... 98
4.3.4 . Conclus io n .............................................................................................................................. 100
CH AP T E R 5 – A COLU MNAR DISC OT IC LIQ UID CRYSTA L UNDER NA NOSCALE C ONFINEMENT ............... 102
5.1. Meso morphic Pro perties o f Bulk .......................................................................................... 103
5.2. Phase Behavior Under Nanoscale Co nfinemen t ........................................................................... 1 05
5.3. Orientational Order un der Nanoscale Confinemen t ..................................................................... 1 12
5.4 . Concl usio n ..................................................................................................................................... 116
CH AP T E R 6 – CON CL USION & OUTLO OK .................................................................................................. 1 19
APPE NDIX I................................................................................................................................................ 128
APPE NDIX II – Supporti ng Info rm atio n for Sectio n 4.1 ............................................................................ 134
APPE NDIX III – Supporting Info rm ation for Section 4 .2 ........................................................................... 146
APPE NDIX IV – Supporting Info rm atio n for Sectio n 4.3 ........................................................................... 1 48
APPE NDIX V – Supporting Inform atio n for Chapt er 5 .............................................................................. 151
APPE NDIX VI ............................................................................................................................................. 1 56
Referen ces ................................................................................................................................................ 1 62

1

CHAPTER 1 – I NTRODUCTI ON
Pl asti cs hav e b een us ed as insulators since the y wer e c onside red as materials do not conduct
electri cit y until t he 1970s. In 1977, c onductive pol ymers were discovered and deve l oped by A l an
Heeger, Alan MacDiarmid, and Hideki Shirakaw a, who w e re award ed b y N ob el Prize in
Chemistry in 2000 for th ei r “ discovery and development of conductive polymers ”. 0F
1 Their discovery
has rev eal ed the possibi lit y of usin g con ju gated or ganic mat eri al s as alterna tive of silicon for
electronic a ppli cations. Th e presen ce o f a conjugated bond s y st em (double bonds ) , consisting of
π - or bitals with deloc alized electro ns, is a prer equ i sit e for conductive pol ymer s. A s an al tern at ive
to conductive (conju gated) pol y m ers , columnar liquid cr ystals (C LC s ) , liq uid crysta l s fo rming a
columnar mesophase, are promising con ju gated mate rials for electronic applications . 1F
2,
2F
3 C LC s
featur es adv antageous p r op erti es for electro nic application s s uch as l ong- ran ge s elf - assembling
abili t y (order), one-dimens ional (1D) charge trans port and light - harves ting abilit y d u e t o t h e π - π
stacked columnar st ructure . 3F
4 Thus, CL Cs are c onsidered as a ne w generation of organic
semiconductors. 4F
5
The char g e carri er mobility and the stabilit y of the columnar mesophase are the most importa nt
prope rties of CLCs for their app lic ations in e l ectronics. Thei r condu cti vit y i s relat ed to t he ch ar ge
carr i er mobilit y, and their phase behavior is as soci at ed with the stability of the columna r st ructu re,
therefore, that of the m esophase. Furthermor e, it is more than like l y that the molec ular mobility
(mol ecular d ynami cs) on di ffer ent tim escal es and the columnar s tructure of C LCs p l a y an
important role for the c onductivit y. 5F
6,
6F
7 Theref or e, the structure, the phase behavior and t h e
mol ecular d y n amics o f C LCs must be r eveal ed . An understanding of the struct ure -propert y

2

relationships, the mole cular mobility as well a s the elec trical conduc tivit y is crucia l to tailor and
to optimize the properties o f C LC s for electr oni c applications.
From t he b asi c res ear ch point of view , C LCs ar e perf ect candidates to st udy the molecular
mobility in s y stems w here order and mobilit y c om petes. This is because the columnar mesophase
has a morphology in bet ween a three - dimensional ordered crystal and a m orphous s y s tems which
can be tune d b y th e chemistr y of the mol ecul es . Thi s concer ns esp eciall y t he glass y d y n ami cs
rela ted to the gla ss transition which has been on e of the in tens el y and controversially d ebated
topics in co ndens ed mat ter s cienc e . The deta iled investiga tion of such ma te rials mig ht shine some
ligh t to understand the gl ass transition not only for C L C s but also for pol y m ers, silicate or metallic
glasse s , for novel t y p es of electrol y t es like ionic liquids, and even for biolog ic al systems such as
proteins or DNA. Because of the fact the struc t ure of the CLCs can b e tun ed b y ch emi str y , s pecial
probl ems can b e addr es s ed li ke sel f - confine ment effects or a glass tra ns ition in lower spatial
dim ensi ons becaus e a sin ce t he col umn s c an be co n sid ered as a on e -dimensional (1D ) fluid. 7F
8
For the applications, C LCs mu st b e confi ned in to a cer tain geom et r y ; thin film s (1D
confinement) or the confi nement into nano chann el s (2D confinement) . The phase behavior under
confinement must be ex plored since the confinem ent influences the phase beh avior. Moreo ver,
f rom the applicatio n poi nt of view , controlling the alignment of columnar direction (mo lecul ar
orderin g) is a pr erequisite. To do so, m any strat egie s h ave been developed to control the alignment
o f C LC s such as ali gnment by surface modifications of the pore walls of confining hosts ,
application of magnetic and elect ric fi eld s, z one casting, etc. 8F
9
Th e aim of this work is to understand molecular d yn amics , phase behavior a nd conductivity of
diffe rent columnar liquid cr y stalline sy stem s and to r eveal t he ir struct u re - property relationship s

3

by employing a combination of different i nvestigation techniques . T h e C LC s select ed and
investig ated in the research work presented in thi s dissertation are s y mmetrical unfun ctionalized
as well as as ymme trical mono -dipole-func ti onaliz ed trip henyle n e - based discotic liquid cry stals
( D LC s ) , triph en ylene cro wn eth er - based unsymmetric al DL C s and colu mna r ionic liquid cry stals .
For this purpose, the molec ular d ynami cs and c onductivity were investigate d b y broadband
diel ectri c spe ctro scop y ( BDS). In addition to the molecular d ynamics probed from the dipole
fluctuations pers pecti ve using BDS , a dvan ced calo rim etric t echniqu es s uch as sp ecifi c he at
spe ctrosco p y (S HS ) and fast scann in g cal ori metr y (FSC) were applied to p robe glas s y d ynami cs
from ent rop y fluctuations perspective . C onventi onal differential scanning calorimetry (DSC)
measureme nt s were conducted to stud y t he phase behavior including the thermal glass tra nsitions
at temperatur es down to 173 K and to 103 K using nitroge n and helium as purge gas es respe ct ivel y.
In addition, it is aimed to explore the phase behavi or and the molecular ordering (alignment) of a
symme trical tripheny lene - based D LC con fined into nanopores. I t is also intended to control the
mol ecular o rd erin g und er t he con fi nemen t b y su rfa ce m odification of the nanopores to achieve the
type of m olecular ordering re qui red for the applications. The molec ular ordering inside the
nanopores wa s det ermined by BDS and the pha se behavior under confinement was explored by
DSC.
This thesis is o rganiz ed as follows. Chapter 1 , i ntroducing to the C LCs and the motivation
behind the research, is f ollowed in Chapter 2 b y an overview of CLCs in the bulk and confined
states as well as glass trans ition and glassy dyna mics. Chapter 3 provi des the fundamental
information about the ma in e x perimen tal techniques. I t starts with givi n g the ide a behind the
investigation strategy using differe nt techniques. Then, it continues with the princ i ples of main

4

chara cteri zat ion techn iqu es . Afte rwa rds , all t he ex peri ment al pro ced ur es and the materials u se d in
this work are introduced in deta il.
Chapter 4 addresses the main results and discussions of different CL Cs in t he bulk state.
Secti on 4.1 presen ts the investig ation of t he mol ecular d y n amics of a sel ected s eri es of dip ole
functionalized tripheny l e ne - based D LCs , which was investig at ed in a s y stematic way to reveal the
phase beha vi or and the mol ecular d ynamics . The inves t igated D LCs are
pent apent y l ox y t ri phen y l en es car r ying eth y l gl y col at e ( SH U09 ), hexanoyl ( SHU10 ),
trifluo romethyl ( S HU11 ) , and dieth y l enegl y c ol ( S HU12 ) units. The meso morphic properties and
the phase behavior of the DL C s SHU09 - SHU12 were s tud ied b y polarizing o ptical micro s cop y
(POM), X - ra y diff r action (XRD), and DS C . Th e mol ecul ar d ynam ics o f al l co mpo unds wer e
investig ated by a combinatio n of state -of -the - art BDS and ad vanc ed cal ori m etric t echni ques such
as F SC and SH S. Gl ass y d ynamics wer e prove n fo r the dete cted proc ess es unambiguousl y due to
the extraordinary bro ad frequency ra n ge covered. The results were compared to the corresponding
unfunc tionalized sy mmetrical DLC ( H AT5 ), which was al so studi ed in this work.
A study on the phas e beh avior an d the molecu lar d y n amics of triphen ylene crown ether - bas ed
D LC s having different length s o f alk y l chain s , is given in Section 4.2 . The phase behavior and the
mol ecular d y n amics were ex p lor ed b y DSC a nd BDS respecti vel y . Secti on 4.3 pres ents the results
of the investigation of the molecular mob ilit y of two linea r - shaped tetra m eth y lated gua nidinium
trifla te ionic liquid c r y st als (IL Cs) having dif f erent leng th s of alk y l ch ai n s using BDS and SHS.
Th e resu lt s ar e discussed in detail, and differen t mo lecul ar as si gnm ents of th e p ro cesses are
suggeste d. Furth ermo re, at hi gher t emp erat ures el ectri cal condu cti vit y is detect ed , and was
anal y z ed i n d etai l . This result is di scussed by a chan ge in the ch ar ge tr an spo rt m echani sm upon
phase transition from the p last ic cr y st all ine p hase t o the columnar mesophase.

5

Chapter 5 provides a s tudy on the ef fect o f c y li nd ri cal con fi nem ent o n th e ph ase beh av ior an d
the molecular ordering of hexakish ex y l ox y tri ph en ylene ( HAT6 ), a tri p hen ylene - b ased DLC,
confined within nanochannels. Anodic aluminum ox ide (AAO) and silica m embranes with var ying
pore diameters, from 161 nm down to 12 nm , were used as confining hosts. Further mor e, it is
aimed to o btai n an ax ial o rderi n g or to i ncrea se t he degree o f ax i al orderi n g b y chem ical
modification of the pore walls. Therefore, both unmodified and modified pore w alls were
consi dered . I n the l att er cas e , t h e pore wal ls o f AAO memb ran es w ere ch emi cal ly t reat ed with
n- octcylphosphonic ac id (OPA) and n - octadecylphosphonic acid (ODPA). The st ud y covers a
broad p ore si ze ran ge, an d t herefo re a mo re det ail ed understanding of the confinement effect on
the phase behavior is obtained. The phase b ehavior was ex plored by differ ent ial s canni n g
calorimetry (DSC) allowing the det ection of changes in th e phase be havior. The pore siz e
dependencies of the phase tra ns ition temperatures were a pp rox imated using the
Gibbs-Thomson- equation, where the estimated surface tension is dependent on the molecular
orderin g of HAT 6 molecule s within the pores. BDS was used to inves tigate the collective
orientational orde r of the mo lecul es of HAT6 conf ined into cylindrical nanopores.
The last b ut not th e leas t, C hapter 6 sum mari zes the research work presented, dr a wi n g a
general co nclu sio n fo r al l the above-mentioned studi es, followed b y a sho rt outlook on the next
int erest ing r ese arch wo rk in the field.

6

CHAPTER 2 – B ACK GR OU N D
2.1 . Co lum nar Liq uid C rysta ls
Liquid cry s tals ( L C s) are unique materials, possessing the properties of both the cr y stalli ne
and the liquid states where t he y h av e liquid crysta lline mesopha ses in the tempe rature range
between thes e t wo s tate s . 9F
10 Mol ecules which f o r m liquid crystalline mesophases have high
orientational and positional order in their cr y stal line phases (order) and low positi onal order in
their liq uid state (mobilit y ) . 1 0F
11 ,
11F
12 Due to the properties of LCs combing that of liquid s and solid
cr ystal s, the y a re sometimes descr i bed as ordered fluids. 13 The featu res of LCs such as their f luidic
and el asti c prop ert ies allow them to respond to differen t types of ex terna l stimuli (e.g . heat, lig ht,
mechan ic al force, el ectri c and magnet ic fi elds ) an d i nteract wit h su rfaces. 1 2F
13 The se featur es b r in g
advantage ous properties f or their application such as eas e o f processabilit y , abilit y of th e ali gnmen t
of the m olecu les b etwee n el ectrod es and self - healing of struc tural d efe cts , wher e cha rge ca rriers
are stu ck at grain boundaries . 13F
14 T h e y als o featu re pr oper ties such as d y nam ic mol ecul ar orde r and
self - assembling as well as anisotr opic optica l, electrical, an d ma gnetic properties. 10 , 12 Due to these
properties, LCs are qualified for a w i de variet y of el ectronic applications. Today, fl at - pan el display
application of LCs is still the most significa nt application o f LC s since LCs are opticall y functional
molecules possessing both optical anisotropy l eadi ng to parallel and perpendicular refraction
eff e cts and fluidity b rin ging c ontrolled switchin g of molec ular alignment under electric fields . 13
The y are als o used in optical connectors, switch es , mo lecul ar sens ors and d et ectors , etc. 1 4F
15 -
15F 16F 17F
18 It i s
important to note that LC s i n gener al are cl assi fi ed ei ther as thermotropic or as l yotr opi c and, i n
the scope of th e res ear ch work p res ented her e, onl y thermotropic L Cs are cons idered.

7

LCs form a r ich var iet y of m esoph ase; smect ic, nem ati c, cho lest eri c, co l umn ar phas es. The
meso phas es are ch ara ct eriz ed ac cordi n g to th eir s y mmetr y in t erms of the or ientational and
trans lat ional de grees of freedom . 10 Among these mesophase s forme d b y LCs , columnar
mesophase, exhibiting long - rang e positiona l/translationa l order in at least one direction and
orientational order, is quite inte resting regar din g the ir a ppl ications. This is due to the fact that
columnar nanostruc t ures , form ed b y th e self - assembl y in a c olum nar mes o phas e , fe atu re 1 D hi gh
charge mobilit y alon g the column axis owing to the delocalization of π - electrons of th e LC
mol ecules . Thi s m akes LCs forming a columnar (columnar liquid cry stal s (C L Cs)) mesophase
promising candidate s for electr onic applicatio ns. Thus, C LC s ha ve gained a growi n g inte rest 1 8F
19
s ince the first clear - cu t report of a columnar m esophase for m ed by a hexasubstituted
benzene- based L C in 19 77 19F
20 . S in ce then , a lar ge nu mber o f C LC s has been s y nthesiz ed. The
m olecu les o f most of the C LC s t yp i c a l l y consist of a ri gid a romatic core and several flexible g roups
( alk yl chain s ) substituted the core b y differen t link ers such as eth er, est er , benz oat e, al kyne, etc.
T he arom atic co re o f C LCs i s us uall y ben zen e or pol yarom ati cs su ch as t riph en ylenes, per ylen es,
hex a - peri -hex abenzocoronenes, triph en ylen e cr o wn eth ers , et c . 4,8 T h e ch emi cal st ru ctu re of
mol ecules of C LC s and t he mes o phase morphologies of C LC s are illustr ated in F igu re 1. D is cotic
liquid cry stals (D L C s ) are t y p ical ex ampl es of C LCs besides others. Furthermore, ionic liquid
cr ystals ( ILCs ) fo rmi ng a col umn ar mes ophas e is also clas sifi ed as C L C s.
The sel f - assembl y of m olecules of C LCs into the columns is driven b y the unfavo rable
int eracti ons b etwe en t h e arom atic cor e and th e flexible substituents (le ading to nanophase
separat ion ) and t he favo r abl e core - cor e int eracti o ns (π - π int eract ion amon g th e aromat ic co res). 3
On the one hand, t he π - π i nterac ti ons of the aro mati c cores s tack ed in the columns also result in
1D high ch ar ge car rier m obili t y alo n g the colu mn ax i s. On the other hand, the flex ible alkyl cha i ns

8

fill th e int ercolu mnar spa ce and act as an insulator. T he flex i bl e alk y l ch ains a re di sor d ered amon g
ordere d columns of the core in t he intercolumnar area. Th is disorder pr events a 3D cr ystal
forma tion while a mesop hase is formed upon cooling from the isotropic p hase. This is ess ent ial
for the for m ation of a colum nar mesophase , wh er e t he nanophase separation between the ordered
columns and the disord ered intercolumnar area is presen t . 8 N anop hase sep ar ati on h as b een
evid enced b y an amorph ous halo observed in the X - ra y patt ern of C LC s . 8 ,
20F
21 Such a nanophase
separa t ion was reported also for differ ent s ystem s su ch as a s eries of poly(n- alk y l acr y l at es) 21F
22 ,
poly(n- alk y l met h acr ylat es) 22 , poly (3 - alk y l t hiophenes) 22F
23 and poly(1,4-phenylene-2,5-n-
dialky lox y terephthalate s ) 23F
24 having longer n- alk y l sid e chain s .

Figure 1 . Chemical structure o f m olec ule s of C LCs; (a) a tri phenylene - bas ed DLC, (b) a gua ni di ni um
pheny lalkoxy be nzoat es

- based columnar ILCs with acy clic guanidinium head grou p and triflat e co unteranion, (c)
a
gua nid i niu m p he n yla lko x ybe nz oa te s

-
base d columnar IL Cs wi th cycli c guani dinium hea d group and t riflat e
co unter a ni on, a nd (d )

a tr iphen yl ene crown ether - b ased D LC. (e) Illustration o f phase be havio r of C LC s and
st ruc t ure
formed in a hexagonal columnar mesophase

b y C LC s (ad apted from ref. 24F 25 )
. For the s ake of sim plicity , dra w ing does
not sh o w alkyl chains and shows o nly aromatic cores for t

he co lu mnar str uc tur e.
An understanding of the structure - property r ela tionships , the mole cular mobility and the
elec trical conduc tivit y is crucia l to tailor and to optimize their prope rties for e le ctron ic
(b)

(c)

(e)

(a)

(d)

9

applications. There fo re, C LC s have been studied b y dif ferential scanning calor i metr y (DSC ),
X- ray diffraction (XRD), neutron scattering, Raman and UV - Vis sp ect ros cop y , nucl ear magnetic
resonance (NMR), optical birefr i ngence, broadba nd dielectric spectroscopy (BDS) , sp ecifi c h eat
spect rosco p y (SHS) , etc. 8, 21 ,
25F
26 -
26F 27F28F2 9F30F31 F32F33F 34F35F3 6F37F38 F 39F
40
2.1.1. Discotic Liquid Crystals
D iscotic liquid crysta ls ( DL C s) consist of molecules that have a disk - lik e (al so bowl- like,
cone- like, or p y ramidal 12 ) rigid a romat ic co res co nnect ed via flexible alky l chains . D LC s form
variet y of columnar mesophase s su ch as squa re, oblique, rectangula r and hexagonal columnar
phases ; t herefo re , the y are classi fied a s C LC s . The hexagona l columnar (Col h ) mes ophas e is
commonly formed b y D LCs, be tween plastic c r ystalline ( C r y) and isotropic ( Is o ) phas es as t he
mol ecules can self - or ganize and stack into hexagon al ord ered columns in a 2D - lattice w h ere
colu mn ax es are parall e l to each ot her . Accord in g to th e classifi cati on o f colu mnar p hases
pio neered b y Ts chiers k e 10 , C ol h phase is describe d b y the plane group p6mm . 8 This cla ssification
is not onl y valid for DLCs but also more generally for CLCs. A n examp le for t he chem ical stru ctur e
of t he molec ule of a D LC and the phase morphologies of D LCs is g i ven in Fi gu r e 2 fo r a
thermotropic tripheny l ene - bas ed D LC . T he red rhombuses shown in Fi gu r e 2 b repr esen t p6mm
plane g roup s. In the scope of the work presented here, onl y C LC s forming Col h m eso phases are
considered.
I t is important to no t e that the plastic crysta lline phase usua ll y formed b y D LCs at low
tempe ratures phase should be ca lled discotic plastic cry stalline p hase to distingu ish it fro m the
plastic cr y stalline that of small molecu les. 40F
41 ,
41F
42 However, this is not generally done in the literature.
Therefo re, in t his presen t ed t hesi s als o th e term pl ast ic cr y st all ine (C r y) ph ase is used .

10

Figure 2 . (a) Chemical structure of molecule of a triph e ny lene - based DLC hexa ki spe nt ylo x ytri phe nylene H AT5 . ( b)
Structures f or med by

HA T5 in d if fer ent p ha se s. F i gure was taken from ref . 4 2F 43 with per mission (see Secti on 4.1
for
the p er mission ).

Application of DL Cs, e.g. as optical compensation films for L C displa y s 43 F
44 ,
44F
45 and g as
sensors 45F
46 ,
46F
47 , are still in the pr oof -of- co ncept stat e . However, r es earch on D LCs o ver th e last
decades has shown that the y can be considered promising materials for use in electronic
applications su ch as o rgani c fiel d - effect tra nsistors (OF ETs), organic lig ht emitting d iodes
(OLEDs) a nd or ganic photovolt aics (OPVs ) beca use the y ex hibit 1D high charge m obilit y alon g
the axis of the column i n Col h mesophase and l ight - harvesting abilit y d ue t o the π - π s ta cked
columnar structure . 5, 13 ,
47F
48 ,
48F
49 Although a number of s tudi es has b een don e and effo rts ha ve be en
made to get an understanding of their intrinsic properties , 13 , 31 ,
49F
50 -
50F 51 F
52 they are not completely
understood . Therefo re, th e y s hould be further investig ated in a s yste m atic wa y and understood to
uncover their fundamental properties and potentia l for applications.
One of t h e first D LCs re ported in the literature is triphen y l enes (triphen ylene - based DLCs ).
T herefo re, most of th e studies were carried out on triphen y lene - b ased D LCs, especi all y on
symmetric triphe n y lenes , in the bulk and under s patial confinement. 8, 10 , 21 , 25 ,
52F
53 ,
53F
54 Beside the
s y m met ric t riph en ylen es , si nce th e earl y work o f R ego 54 F
55 , Kilburn 55F
56 , Cooke 56F
57 , Kumar 57 F
58 , and
Kell y 58F
59 there is also a consider able interest in d ipole function alized low sy mmetr y
trip hen ylenes , 5 9F
60 ,
60F
61 because they can be used as build ing blocks in liquid cr ystalline dimers an d
hy brid materials. 8 Rec ent studi es on such tripheny l ene derivatives revealed promising
(a)

(b)

11

self - assembl y and photophysica l properties, e.g. blue - light e mitters 61F
62 and high birefringence,
which are useful for terahertz communication optica l elements, optical attenua t ors and hologr aphi c
devi ces. 62F
63 As me ntioned in Introduction in general for CLCs, al so low sy mmetr y
triphe n y len e - based DLCs ar e unique materia ls , wh ich ca n provid e knowled ge to un cover the glass
transition phenomena , a longstanding topical problem of condensed matter science . Investigating
the molecular mobilit y i n such a s ystem where order and mobilit y competes , helps to gain an
insight into the glass tran sition phenomena. Moreover, the st ructure of the se D LC s can b e tun ed
by chemistry . Th is ability to tailor their structure c an provide opportunit y to address a glass
trans ition in in terco lum nar are a and/or in intracolumnar area . For example, a dipole
functionalization of the core of molecules of a DLC allows t o probe t he glas s y d ynamics
( molecu lar mob ilit y related to a glass tra nsition) in the int ra colum na r ar ea u sin g BDS (see r ef.s 39
and 6 3F 64 ). Since the columns can be considered as on e - dimen sional fluid 8 , a glass transition taking
place i n th e int ra co lum na r are a can be consider ed as a gla ss transition of on e- dimensiona l fluid .
The competition i n D LC s takes pl ace betw een th e or dered col um ns fo rm ed b y the aromat ic
core s and t he disordered substituents fill ing the interc olum nar space . Moreover, such a compe tition
in t he in tracol um nar area might presumabl y o ccu r between the ordered par t of the columns and the
disordered por t ion of the columns, where packing frustrations are pr esent ( Fi gu re 2 b ). Fr om the
basi c res earch point of view , it is inter esting to s tudy these comple x liquid c r y stalline systems
where orde r and m obilit y compete . As i t is also m entioned in Introduction , t his i s because di ffer en t
physica l phenomena, for instance self - confi nemen t effect s and/or a gla ss transition in low er spatia l
dimensions ( one- dime nsional fluid ), can b e add res sed b y inves ti gati ng the mo lecul ar d y nami cs o f
thes e s y s tem s. T here are only a few number of studies reporting a glass transition observed in th e
C r y phase for columnar D L Cs. 21 , 25 , 35 - 38 , 49 , 64 For p lastic cr y st als , a glass tran s iti on was repor ted b y

12

Suga and Seki for the first time . 64F
65 Further ex amples for g l ass y d y namics in plastic and also condi s
(conforma t ionall y disordered) cr yst als are d iscu ss ed i n l iterat ure (s ee r ef. s 65 F 66- 6 6F 67 F6 8F 69 ).
I t is more than like l y that the mole cular mobility i n both the Cry and the Col h phases of D LC s
plays an important role for the conductivit y. 6,7 A change in the conductivit y at the pha s e transition
from th e Cry ph as e to the Col h phase can be u s ed as a switch in the application where for
field - ef fect transistors conductivity in the liqui d cry st alline phase has to be considered. Therefo re,
investig ation s on the mo lecula r mobility and understanding of it are highl y demanded f rom bot h
fundamental research a n d application point of views.
Wert h et al . 69 F
70 reported diff erent monofunctiona lization of the s y mmetrical triphen y l ene
hexakispenty lox y t riphenylene HAT5 with an ester group, which prevents cr y st allization.
Consequently, a glass y columnar phase is formed. Their study illustrates furthe r that small
molecular structural cha n ges, such as dipole functionalization, m ay considerably affect the phase
behavior due to the spe c ific conformation of the f unctional group including dipole interactions.
Such a dipole functionaliz ation gives not onl y t he possibili ty to stud y i ts effect on the phase
behavior but also ena bles to i nvestigate t he molecular dyna m ics including p ossible g l ass y
dy namics using BDS. I n the literature, dip ole functiona lized low s y mm etr y
hexabenzocoronene- b ased DL C s wer e studied to inve stigate the molecula r dynamics including
gla ss d y namics using BDS. 37 , 39 , 64 In general, BDS is a pow erful tool to ex plore the molecular
dyna m ics with a hi gh sens itivit y over a broad frequenc y a nd temperature ra nge. The investigation
of the molecular d y namics of sy mmetrical DL Cs using BDS is c halleng in g and limited to a certa in
extent due to their weak dipole movement.

13

2.1.2. Discotic Liquid Crystals Under Nanos cal e Co nf in ement
DLCs can also be nanoconfined into a specific geometr y , e. g . as thin films or in cy lindrical
nanochannels, in order to opti mize their use in e lectronic applications. Metal ox ide membranes
that have a pa rallel ali gnment of cy l indrical nanopores and nar ro w pore size distribution , can be
produ ced b y ele ctro che mical e tching. Confinin g DLCs into the c ylindrical nanopores of metal
oxide membranes has g ained much interest. This is due to the fact that i nvestigations on such
confined systems can address fundamental questi ons such as phase behavi or and glass transition
d yna mics, whilst also helping to shed light upon the structure - property relationship of soft matter
syste ms under confinement. 50 , 52 Moreover, fr om t he application point of view , it opens up the
possibilit y to prepare nanowires through the dissolution of the host membrane since the columns
formed b y D LCs can be considered as isolated, o ne-dimensional, conducting nanowires. 70F
71
Nanoconfine m ent influe nces the properties of DLCs like for other soft mater s y st ems 7 1F
72 whi ch
have t o be rev eal ed fo r th e appl icat ion s at t he na no scale. The phase behavior under confinement
and the molecular orderin g of DL C s within pore structures are two of the m ain properties def ini ng
their applications in nan otechnolog y . 5 Hen ce, se veral i nves ti gation s hav e b een car ried o ut t o
elucidate the pha se beh avior and molecular orde r ing of DLCs confined within the nanopores of
metal ox id e mem branes . 31 , 51 , 52 ,
72F
73 -
73F7 4F
75 Compared to b ulk DLCs, a decrease in phase transition
temp eratur es is o bserv ed al ong with the f ormation of additional structures u nder confinement that
has been reported for p yrene - and triphenyle ne - based DLCs. 50 , 52 , 74 On the other hand, controlling
the m olecu lar o rder in g w ithin the pore structures is highl y desir able for im proving a ppl ication
relevant properties such as conductivity and light - harvesting abilities. He n ce, alig nin g the co lumns
of D LC s paralle l to th e ax is o f the po res is t herefor e cruci al for their success in s pe cific
applications.

14

Figure 3. Types of mole cular orderin g of D LCs unde r confin e ment (a) Home otropic (f ace - on) ali gn me nt and (b )
planar (edge

-
on) alignment on a free surface. (c) Ho m eo tropic radial configurati o n, (d) p lanar axial co nfiguration, (e)
planar radial configuration , and (f) ano the r p la nar a xia l co nf ig ura tio n d o mina tin g c o nfi gur a tio n t yp e i nsid e a
cyl indrical channel with a di sordered isot ropic core . For th e sake of s i mpli city, draw i ngs do not sh o w alky l chains a nd
show o nly aromatic cores for the molecular ordering. Fig ur e wa

s ta ke n fr o m r e f. 25 wit h pe rmi ssio n ( see
Chapt er 5
for the per mission ).

Pl anar (ed ge - on anchoring) and homeotropic (face - on anchoring) align men ts ar e the t wo
poss ib le t ypes o f m olecu l ar ord eri n g of D LC m ol ecul es wit h res p ect to a f lat surf ace ( Fi gu re 3 a
and Fi gu r e 3 b). These two alignments describe the ordering in thin films of DLCs and DLCs
conf ined between two paralle l solid substrate s. 26 However, b y confinin g DL Cs withi n cy lindri cal
pores, describ in g the molecular or de ring become s mo re comp li cated. Th e mol ecul es of t he
confined DLCs possess multiple t y pes of ord ering, and thus, describing this ordering within
cy l indrical pores solel y as planar o r homeotropi c is insufficient. Hence, additional directional
chara cteri zat ion term s su ch as ‘a x ial’ and ‘radial’ should be use d t oge t her with the anchor ing t y p e
for cla ri t y. It has b een sho wn th at pl ana r ax ial , pl anar radi al (circu l ar con cent ric ) 54 ,
75F
76 an d
homeotropic radial (logpile) 76 F
77 configurations are the pr edominant forms of orderin g within
cy lindrical pore structures ( Fi gu r e 3c- f). There is a competition between these configurations,
(a)

(b)

(c)

(d)

(e)

(f)

15

caused by different interfacial t ensions observed between air/liquid cr y st al, liquid cr ystal/pore
walls and liquid cr ystal/liquid cry st al. The domi nating type defines the configuration for the
overal l s y stem.
Among the a bove - m entioned types of confi gurations found within the po res, onl y the axi al
config u ration is suitable for electronic applications. Studies have shown that axi al config u rations
are sc arcel y ach iev ed , whereas homeotropic radial and planar r adi al configurations are more
commonly obs erved for DLCs conf ined within t he nanopores of m etal oxide membrane s. 31 , 54 , 73 - 77
However, a dominating ax ial configura ti on might be obtained through c h emical modification of
the p ore su rfa ce. 31 Besid e t he sur fac e mo dif icati o ns ch an gin g the ho st - gue st interactions, a proper
choice of the host pore size with respect to that of the g uest D LC can lea d to better configurational
control. R ecentl y, Zhan g et al. 76 reported that th e dominating ordering ty p e changes with pore
size . 76 , 77 Furthermore, they observed a transition from a planar radial configuration to an axial
config u ration with increasing columna r rigidit y of the DLC. 76 The column rigidity increa s es with
aromatic core size, hence, it can be tuned to obtain the desired configuration through proper choice
of the DLC.
2.1.2. Ionic Liquid Crystals
Ionic l iquid cr y st als ( ILCs) are c l assified as liquid crystalline compounds containing a ni ons
and cations. They combi ne the proper t ies of LCs and ionic liquids such a s d y namic molecular
order, self - assembl y, a nis otropic ph y si cal properties with ionic conductivity . Ionic conductivit y in
that case is t he chara cter i sti c prop ert y of ILCs t h at di fferent iat e t hem f ro m con vent ion al LCs. 7 7F
78
Similar to DL C s, ILCs can also form c ol umnar mesophases. 78 , 79 Columnar IL C s possess both ion
conductivity a nd hi gh ch arge carrier mobility along the column axis.

16

Recent l y, Ax enov and Lasch at 78F
79 as well as Bi nne man s 78 have published reviews on ILCs
including also a discussion of the columnar case. As it is reported in the se r evie ws , ILCs are
curre nt l y receiving a great interest as highl y c onductive solid - state electroly tes, nonvolatile
phase- chan ge (en er g y sto rage) mat erials , catal yst s, n ano com pos ites , s eparat io n m emb ranes,
proton- conducting membra nes for applications in mol ecul ar electr oni cs , bat teri es, fu el cell s,
memb rane and cap aci tor s . Columnar ILC s are m ore promising c andidates for the most these
applications, espec i all y for applica ti ons in molecular elec t ronics, due to their anisotropic 1D ionic
conductivity feat ure i n a Col h mesophase. Furthermore, most lite rature works about columnar IL Cs
cited in t hese rev iews fo cused on t he s ynthesi s and t he char acter iz ati o n of t he mesomorphic
properties by DSC, XR D as well as polar i zed optical microsc op y (POM). 79F
80 -
80F 81F82F83 F 84 F
85 On l y a few studi es
investigating the ionic conduc ti vit y of the colum nar IL C s have been reported. 85F
86 -
86F 87 F8 8F
89 Ther efor e , a
molecular leve l understanding of the dy namics and of the conductivit y of IL Cs is required to
design and tune their pr operties for the electronic applications as general ly di scussed for C LC s
above.
2.2. Glass Tran siti on and G lass y Dyn am ics
Her e in this se ction, both the thermody namic and kinetic aspects of the g lass transition are
discussed . F urthe rmore, a n understanding of the underly in g ph y si cs of glass - forming materials is
introduced.
2.2.1. Glass Transition
The g lass transition is a th erm o - kinetic phenomenon . 89F
90 It d eterm ines the u se tem peratu re fo r
practi cal app li cat ion s and proces sin g tempe rat ur e for gl ass - forming materia ls. 9 0F
91 Glass - formin g
mater ials , includ ing a w ide v ariet y of m at erial s ran ging from m etals and liqui ds to pol y me rs ,

17

solidif ies as glass es rat her than cr ystals. Glas s - f orm ing mat eri als ex perien ce a dr ast ic ki neti c
slowdown of the molecular dyna mics wh en t h ey ar e cool ed to w ard thei r glass tr ansi ti on
temperature without an y obvious structural change. 9 1F
92 Understanding the ori gin of this behavior as
well as the underlying physics of gla ss - form ers i s a major sc ientific c hallenge. Although gla ss
transition has been extensivel y studi ed, it has bee n on a debate in cond ensed matter s cien ce fo r a
long time and i s still not fully understood.
The tem per atu re d epend en ce o f the cha ract eri st ic th ermod y n amic q u anti ti es su ch as sp eci fic
volume and enthalpy changes but continuousl y up on the glass transition, where the mid - point of
this region is often defined as ther mal gla ss transition temp eratur e (T g th erm al ). Due t o the continuity
of the ch ange in th e chara ct eristic thermod y na mic quan tities upon a gla ss tr ansition, g lass
transition is not a phase transition. I nd eed, it is a t herm o -kinetic phenomen on (see Fi gu r e 4 a).
At hig h temperatur es, a glas s - former flows mo re or less li ke an ordinar y fluid, which ha s a
shear modulus value of approximatel y z ero. Cooling a gl as s - form er m aterial o r s yste m from its
liquid state without cr ysta l lizing, inc reases its density and viscosity . A s a re sult, the molecular
motions slow down. Th e s uper cool ed m el t beh av es li ke a vi sco elas ti c m ateri al . I n a ce rtain
temp eratur e ran ge , th e ch aract eris ti c time of the molec ular motions re sponsible for the structu ral
rea rm ament o f the molecules in to a thermodyn a mics equ ilibrium state be comes longe r than the
tim escal e of the ex peri men t. Cons equently , the s ystem fall s out of equilibr ium and freeze s into a
non- equilib rium di sordered glas s y stat e without having long - range o rder, w here t he s ystem can be
consi dered as gl ass due its ex ceedingl y hi gh viscosit y. At this transition, the shear modulus
increas es , consequentl y , t he shear modulus of the glass is in order of magni tude of approx i matel y
10 9 Pa – 10 10 Pa . This rev ersib le transition proce ss from the e quilibrium state to the solid - like
glass y st at e takes place o v er a ce rt ain t empe rat ur e ran ge, call ed th e glass transition re gion, which

18

is ch aract eriz ed b y t he T g t h erm al . A bove T g th erm al , the st ate of t he glass - fo rm er s is call ed sup ercool ed
melt , and be l ow T g th erma l t he st ate i s refe rred as gl ass y state ( Fi gur e 4b). The short - range orde r of
the g lass y state is similar to tha t of the super cooled melt.
T g,2
T g,1
Slower cooling
Faster cooling
Equilibrium line
(equilibrium)
(non-equilibrium)
Glassy state
Specific Volume, Enthalpy, Entropy
Temperature
Rubbery-liquid state
T m

Region
Supercooled Melt
Glass
Transition
Specific Heat,
Expansion Coefficient , etc.
Temperature
Glass

Figure 4. A schemati c o f the t her m a l glas s transitio n (a) T he tem per ature dependence of specific volume or enthalpy
for a glass

- form er, expos ed to diff erent cool ing rat es. T m
stands for a (hypotheti cal) melting temperature and solid
black lin e rep resents th e ca se o f

a melting pr ocess. (b) Tem perat ure dependence of the material properties
of the
glas s - fo rm ers a t the glas s transitio n. Figure was adapted from ref . 92F 93 .

(a)

(b)

19

T g th erm al depends on the cooling rate. Upon faster cooling, a g l ass - fo rm ing m ateri al falls out of
the equilibrium state at a higher temperature than that observed in the c ase of slower cooling as
shown in Fi gu r e 4a. Thus, a higher cooli ng rate re s ulting in a higher T g t h erm al .
2.2.2. Glassy Dynamics
Mol ecular d y n am ics r el at ed t o g las s y dynamics occur at tim escal es cove ri ng mor e th an 12
orders of magnitude from pi coseconds to seconds and even lon ger. There for e, gl ass y d y n ami cs
have bee n st udied in a w i de range of frequency windows by var i ous methods l ike dy namic
mechan ic al anal y s is ( DM A ), 93F
94 neutro n scattering , 9 4F
95 light sca tte ring , 95F
96 nu clear m agn eti c reson ance
(NMR), 96F
97 SHS 97F
98 and esp eci ally BDS 9 8F
99 ,
99F
100 .

(localized motion)
β -relaxation
f max,1 < f max,2
log ε ''
log f
T 1 < T 2
α -relaxation (cooperative motion)

Figure 5 . S che matic representation of a typical dielectric loss spectra in a broad frequency range for two tem p eratures
T

1 – bla ck solid line - a nd T 2 – red s o lid line. Two relaxation p rocesses, the α -
rela xatio n (dyna mic glass transitio n) and
the β

- relaxation, are in dicated. Figure was adapted from ref. 101 .
Fi gu r e 5 gives a s chem at ic o vervi ew abo ut t he di fferent d ynamic al p rocess es tak ing pl ace in
gla s s - forming mate rials giv en in dielec tric loss spec tra obtained from BDS as an ex ampl e . The
diel ectri c spe ctra s ho w two diel ectri c relax ati on p rocess es, indicated as p eaks, α - and
β - relax ati ons . The asymmet ric p eak at lo w fr eque ncies (hi gh temp erat ur es) is th e α - process w hich

20

is al so cal led as glas s y d y n ami cs . Fo r a gl as s - form er, β - pro ces s app ea rs at h igh er fr equen ci es (lo w
temperatures) which is re lated to localized motions having a relative l y shorter le ngth scale
compared to the t y p ical 1 -3 nm len gth sc al e of α - p rocess at gla ss transition te mperature 106 . Above
T g th erm al , cooperative molecular motions responsible f or the glass y d yna m ics are active. Fo r the
temp eratur es belo w T g th erm al , t he cooper ative molecular motions corr espond ing to the α - pro cess is
frozen, however, localized fluctuations ( β - pro cess) might still be act ive.
T he relax at ion rate s 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 of a p rocess are d ete rmi ned fro m th e relax at ion peak s i n di electr ic
spect ra . For a di electri c relax at ion proces s, 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 is defi n ed as t h e f requen c y at w hich the dielectric
loss is maximu m (s ee 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 , 1 and 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 , 2 in Fi gur e 5). F or the quantitative a nal y sis , the te mperature
depend en cies o f r elax ati on rat es ar e commonl y pre sented in a relax ation map , which is also call ed
activation plot or Arrhe n ius plot . In r elaxation map, the rel ax ati on rat e s ar e plo tt ed as a fu ncti on
of recip ro cal t empe ratu r e , given in F igu re 6 a as an ex am ple.

-4
-2
0
2
4
6
8
1000/T
g
dynamic
c
P
1000/T
1000/T
g
thermal
α -relaxation
log (f
max
[Hz])
β -relaxation

Figure 6 . Schematic ill ustratio ns of t he dynamics taking place at a glass transition for a gla ss - for mer. (a) Relaxation
ma p f o r t he α

- a n d t h e β - relaxation processes . T he form er can be described by a V FT - equa tio n ( eqn . ( 2)
) and the latter
follo ws

an Arrheni us - depen de ncy ( eq n. (1) ) (b) Sp ecific heat capacity , c p , as func t io n o f i nverse temperature . T g
thermal
is determined a s the middle point temperat ure o f the step

- like chang e i n the s p ecific heat capacity . F igure wa s
adapted
fro m r e f. 10 0F 101 .

(b)

(a)

21

On th e one h and, t he tem perat ure dep en den ce o f th e relax at ion rates o f a β - relaxat ion is a
straig ht line as exp ected when plotted versus inverse temperature i n a r elaxation map, which
ind icates localized molecular fluc tuations ( β - process in Fi gur e 6a). T he temperature dependence
of th e relax ati on r ates o f t he β - relax at io n fol lows general l y th e Ar rheni us - equation
𝑙𝑙𝑙𝑙𝑙𝑙 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 = 𝑙𝑙𝑙𝑙𝑙𝑙 𝑓𝑓 ∞ − 𝐸𝐸 𝐴𝐴
𝑙𝑙𝑙𝑙 ( 10 ) 𝑅𝑅𝑅𝑅

(1)
Here 𝑓𝑓 ∞ is the re laxation rate at infinite te mperature , 𝐸𝐸 𝐴𝐴 sy mbolizes the activ atio n ene r gy a nd R is
the gas constant. On the other hand, t h e temp era t ure dep en denc e of th e rel ax ati on rat es of an
α - relax at ion is curve d when plotted in a relax ation map ( α - process in Fi gu re 6a). Such a
temp eratur e dep enden ce of t he rel ax atio n rat es can be cons idered as an in dicat io n of glas s y
d y n amics ( α - relax at ion ) and can be wel l - app rox imat ed b y t h e empirica l V oge l/ Fulche r/Tammann
(VFT - ) equ at ion 101F
102
𝑙𝑙𝑙𝑙𝑙𝑙 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 = 𝑙𝑙𝑙𝑙𝑙𝑙 𝑓𝑓 ∞ − 1
𝑙𝑙𝑙𝑙 ( 10 ) 𝐷𝐷 𝑅𝑅 0
𝑅𝑅 − 𝑅𝑅 0

(2)
where 𝑅𝑅 0 is the so - ca l led Vogel or ideal glass transition temperature which is often found for
conventional g lass - forming syste ms to be 30 – 70 K below the therma l glass tran sition tempera tur e.
𝐷𝐷 is the so - c alled fra gility par ameter or fra gility strength and provide s a parame ter to classify
gla s s - forming sy stems into fra gile an d strong glasses . Gl ass - forming sy stems are c alled “frag ile”
when the temperature dependence of t he relaxation rates of an α - rel ax ati on devia t es strongl y from
Arrhenius-behavior, and "strong" w hen that of an α - rel ax ati on is clos e t o Arrhenius -behavior. I t is
worth to note that a lso conventional glass - forming materials shows a crossover behavior of the
α - relax at ion , where t h e t emperat ur e d epend en ce of t he relax atio n rates of an α - relax atio n has a
trans ition from the V FT - behavior to the Arrhenius-behavior. 10 2F
103 ,
103F
104 The crossover behavior mig ht

22

be ex pl ained b y t he co operat iv it y appro ach to th e glas s t ransi ti on pi oneered b y Adam and
Gibbs. 104 F
105
As alr ead y menti oned ab o ve an d can be s een from F i gu r e 6b , the rel ax at ion shows u p as a s tep -
like change in the spec ifi c he at c apaci t y (c p ), indicating a thermal glass transition. At T g th erm al , t he
relax ati on rat e of glas s dynam ics h as re ached a t ypical val ue of ~10 -2 H z ( Figu re 6 ). This value of
the rel ax ati on rat e is a good approximation for a T g t h erma l obtained from DS C experiments run at a
stan dard he ating/ cooling rate of 10 K min -1 . However, the rel ax atio n rate corresponding to a
T g th erm al can b e acc urat el y estimated rather than using the t y pi cal value o f ~10 -2 Hz in ord er to
comp are it with the relax at io n rates est imat ed fro m BDS meas ur ement s as wel l as from the o ther
methods probing g lass d y n amics . Donth derived a relationship between the he ating / cooling r ate
and the relaxation r ate in the frame of th e fluctuation app roach to the glass transitio n 93 ,
105F
106 , whic h
is
𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 = Ṫ
2 𝜋𝜋 𝑎𝑎 ∆𝑅𝑅 𝑔𝑔

(3)
Here Ṫ is the hea tin g /cooling rate and 𝛥𝛥𝑅𝑅 𝑔𝑔 is the width of the glass transition. 𝑎𝑎 is a const ant with
a valu e o f approx i mat ely on e. 𝛥𝛥𝑅𝑅 𝑔𝑔 was es ti mated as the d iffe renc e bet w een the en dset and t h e
onset temperatures of the step of the glass transition.

23

CHAPTER 3 – E XPERIMENTAL T ECHNIQUE S
Differ ent ex p erim ental t echniques w ere u sed in a compl e ment ar y wa y in this work. The mai n
techniques used in this work are broa db and di electric spectroscopy (BDS) , spe cifi c he at
spect rosco p y (SH S) , di ff erenti al s canni n g calo rimet r y (DSC ) and fas t scan n ing calo rim etr y (FS C).
In a ddit ion, thermog ravi m etri c anal y si s ( TG A), Fou rier trans fo rm in frared sp ectroscop y (FT IR),
pol arizing o ptica l m icrosco p y (POM) , small - angle and wide - an gle X- ra y scat teri n g (SAXS and
WAXS ) are al so used as compl e men tar y tech niq u es. Th e main idea b e hin d us ing the se d iffe rent
techniques is giv en as foll ows. Investigation of all C LC in this work sta rt s with the determination
of its the rmal decomposition tempe ratures using TGA. The d etermine d thermal decompo sition
temp eratur e i s th e upper t emper ature limit for the sample p reparation s (including both the samp le
prepar ati on for the invest igation of a C LC under confinement and t he prep ar ation of the samples
for th e me asurem ent s) an d meas urem ents . After th at conventional DSC experiments are conducted
to dete rmine phase tra n sition tempe ratures a nd entha lpies as well as the rmal glass tr ansition
temp eratur e. Deter minin g the c learing temper atu re s ( the phase transition temperature of the
transition from Col h phase to Iso phase ) b y t h e DSC ex peri ment s i s req ui red fo r t he sample
prepar ati on . It is need ed , sin ce t he sampl e p repa rat io ns t ake pl ace in the isotropic liquid ( Is o ) phase
of the C LC s , at tem pera tu res abo ve their cle ari ng tem per atu re and b el ow t he ir decompositi on
tempe rature. Afte r this step, the investig ations of t h e C LC s in bulk state a nd under confinement
procee ds di fferentl y . In the bulk investigations, th e mo lecul ar d y n ami cs is investig ated first using
BDS. If glass y d ynami cs are d et ected u sin g BDS a nd a thermal gla ss transition by D S C, the gla ss
dyna m ics are further invest igated b y S HS and/or FSC . POM and XR D are u s ed t o ch ar acteri ze t h e
liquid cry stalline texture and str uct ure.

24

For the samples for the investiga t ion of a C L C un der confinement, BDS is used to determine
the c ollective orienta tion al ord e r. In the investigation of a C L C unde r confinement , FT IR is used
to confirm the surface modification and XRD to estimate the thickness of t he su rfa ce co atin gs .
I n this chapter, the princi ples of the m ain ch ar act eri z atio n techniques us ed in t his work are
briefl y i ntroduced. After tha t, the ex peri ment al p rocedu res o f th e mai n char a cteri zat ion techn iqu es
and all other complementary techniques used in t his work are described in detail. La s tl y , the
sample preparation for the investiga ti on of a CLC embedd ed into unmodified and modified
nanopores of me m branes, including the deta i led description of t he surface modifica t ion process as
well as th e characterization of unmodified and modified membranes are elu ci dat ed.
3 .1 . Prin ciple s of Main Expe rim enta l Tech niqu es
The mai n characterization techniques used in thi s work are b roadband dielectric spectroscop y
(BDS ) and specif i c heat s pectro scop y (SHS) . Both BD S and SHS are based on the l ine ar response
theory ( LR T ) . 10 6F
107 ,
107F
108 L R T de scri bes t he rel at ion betw een an input (disturbance) and an ou t put
(respons e) fo r a s ystem a nd provides a framework in order to describ e d ynamic prope rties of a so ft
matter s y stem. In L RT, a n outer disturbance x (t) ( ex t ernal pertur bation) appl ied on a s y st em m a y
cause a res pons e y(t), which is lin ear to the applied pe rturbation . 99 I n other words, the
time - depe ndent r esponse of the system, ca us e d by the time - depend ent p ro cesses tak in g place i n
the system, to the disturbance c an be described b y a linear equation. The time - dependent processes
in the sys tem c an be probed b y applying a sm al l ou ter disturbance to th e s ystem. Outer disturbance
x (t) can b e temp eratu re, elect ric fi eld, shea r fo rce or magne tic field. D ifferent outer d i s tu rbances
y i el d di ffe rent r esponses . However, di fferent outer disturbances applied to a s y stem allow to probe
differe nt aspect of th e same process in the s y stem. Thus, combination of different techniques based

25

on linear response theory is advantage ous in o rder to un derst and an d rev eal a pro ces s in a s ystem
from d ifferen t pers p ecti v es in a comp lemen tar y manner . For ex amp le, BDS pro bes m olecu lar
dyna m ics from the dipo le fluctuations perspective, on the other hand, SHS probes the same
molec ular d y namics from the en thal p y fluct uati o ns p erspect iv e.
3 .1.1 . Bro ad ban d Diel ectric S pect ros copy
Broa db and dielectric spectroscop y (BDS ) is a po werful and ver satile technique to study the
mol ecular d y n am ics of polar liquids, b iological sy s tems, pol y mers, LC s and so on. BDS can be
defin ed as t he m easur em ent of t he di electri c pro p erties of a material u nder investig ation through
the interaction of electro magn etic w aves wi th m atter in the fre quenc y r ange from 10 -4 H z t o 1 0 12
Hz. The dielect ric p roper ti es o f a mater ial are defined b y the pro cesses taki ng place in t he mat erial
such as the molecular dipole fluctuations, collective dipole fluctuations, charge transport and
polarization effec t s at inner and outer boundari es. Thus, BDS is used to investigate the molecular
dy namics including gla s s y d ynamics , ch ar ge t ran spo rt (el ect ric con duct ivi t y) and the collective
orientational orde r of C LC s in the bulk and the confined state. This s ection is based on ref .s 99,
100 and 10 8F 109.
T he r el ation be tween s mall ele ctric field str e ngth 𝐸𝐸 ( ≤ 10 6 V m -1 ) and the d iel ectri c
dis placem ent 𝐷𝐷 can be ex pr ess ed as
𝐷𝐷 ( 𝜔𝜔 ) = 𝜀𝜀 ∗ ( 𝜔𝜔 ) 𝜀𝜀 0 𝐸𝐸 ( 𝜔𝜔 )

(4)

where ε 0 is the diele ctric p ermittivity of vacuum ( 𝜀𝜀 0 = 8.854 10 - 12 AsV -1 m -1 ) and 𝜔𝜔 is t he angular
frequen c y ( 𝜔𝜔 = 2 𝜋𝜋𝑓𝑓 ). 𝜀𝜀 ∗ is t he com plex d ielect ric permittivity .
Wh en an ex ter nal el ectri c fiel d appl ied to a mate rial, the r esponse o f the m ateri al cau ses t he
diele ctric displa c ement which is described by the p olarization P ( Fi gur e 7)

26

𝑃𝑃 ( 𝜔𝜔 ) = 𝐷𝐷 ( 𝜔𝜔 ) − 𝐷𝐷 0 = ( 𝜀𝜀 ∗ ( 𝜔𝜔 ) − 1) 𝜀𝜀 0 𝐸𝐸 ( 𝜔𝜔 ) = 𝜒𝜒 ∗ ( 𝜔𝜔 ) 𝜀𝜀 0 𝐸𝐸 ( 𝜔𝜔 )

with
𝜒𝜒 ∗ ( 𝜔𝜔 ) = ( 𝜀𝜀 ∗ ( 𝜔𝜔 ) − 1)

(5)

where 𝜒𝜒 ∗ is the die lectric susce ptibilit y .

Figure 7. Schematic representation of LR T for the case of BDS.

In macro scop ic sc ale, 𝑃𝑃 i s the sum of microscopic dipole moments, can have e ither a permane nt
or an induced character, i n a volume. Disturbing the natural char ge distribution b y a lo cal elect ric
filed r esults in an induce d polarization. Electr onic polarization ( the shift of the electron cloud of
an ato m wi th res pect t o the n ucleu s ) and atomic polar iz ation are th e t ypi cal t ypes of induced
polarization. Additiona lly, man y m ol ecul es c arr y per man ent dip ole m o vemen t du e t o their
chemi cal st ruct ur e. App l y i ng an ex t ernal electr i c fi eld causes an orientational polariz ation of t he
permanent dipoles in a m olecu le . Under the assum ption of non - intera cting dipoles, the contribution
of the orientational polar i zations corresponds to dielectri c str en gth ( ∆𝜀𝜀 ) for a given dipole densit y
and t emperat u re.
Wh e n the applied electric field is periodic in a stationary sta te , 𝐸𝐸 ( 𝑡𝑡 ) ( 𝜔𝜔 ) = 𝐸𝐸 0 𝑒𝑒 − 𝑖𝑖𝑖𝑖𝑖𝑖 ; wher e 𝑖𝑖 =
√ − 1 , the phase-shifted polarization is the response ( Figur e 8 ), and eq n. (5) is Fourier transformed,
consequently , becomes
𝑃𝑃 ( 𝑡𝑡 ) = ( 𝜀𝜀 ∗ ( 𝜔𝜔 ) − 1 ) 𝜀𝜀 0 𝐸𝐸 ( 𝑡𝑡 )

(6)

27

where 𝜀𝜀 ∗ ( 𝜔𝜔 ) = 𝜀𝜀′ ( 𝜔𝜔 ) − 𝑖𝑖𝜀𝜀 ′′ ( 𝜔𝜔 ) is the comple x die lectric permittiv it y ( or the complex dielec tric
function ) and 𝛿𝛿 is the phase shift , wher e tan 𝛿𝛿 = 𝜀𝜀 ′′
𝜀𝜀 ′ . On the one hand, 𝜀𝜀′ ( 𝜔𝜔 ) is th e real pa rt of the
complex dielectric function, and r elated to the energy stored reversibly during one c y cle. 𝜀𝜀′ ( 𝜔𝜔 ) is
in -p hase with 𝐸𝐸 ( 𝑡𝑡 ) . On the other hand, 𝜀𝜀 ′′ ( 𝜔𝜔 ) is the imag ina r y part ( or the loss part) o f th e comp lex
diel ectri c function and relat ed t o th e ener g y dissipated during on e c y cle. 𝜀𝜀 ′′ ( 𝜔𝜔 ) is often call ed as
diel ectri c los s and is 90º-phase-shifted to 𝐸𝐸 ( 𝑡𝑡 ) .

Figure 8 . Schemati c r elationships between the time dependen ce o f th e periodic electr ic field 𝐸𝐸 ( 𝑡𝑡 ) and that o f the
periodi c phase - shifte d po larization 𝑃𝑃 ( 𝑡𝑡 ) in the framework of LRT for the cas e o f BDS.

One - sided Fourier or full im ag i nar y L aplace transf ormation is applied to obtain the relationship
of 𝜀𝜀 ∗ ( 𝜔𝜔 ) to the time - depend ent di electri c fun ct ion 𝜀𝜀 ( 𝑡𝑡 )
𝜀𝜀 ∗ ( 𝜔𝜔 ) = 𝜀𝜀 ′ ( 𝜔𝜔 ) − 𝑖𝑖 𝜀𝜀 ′′ ( 𝜔𝜔 ) = 𝜀𝜀 ∞ − � 𝑑𝑑𝜀𝜀 ( 𝑡𝑡 )
𝑑𝑑𝑡𝑡 𝑒𝑒 − 𝑖𝑖𝑖𝑖𝑖𝑖 𝑑𝑑𝑡𝑡
∞
0

(7)
where 𝜀𝜀 ∞ represent s t he r eal part 𝜀𝜀 ′ i n the limit of 𝜀𝜀 ∞ = 𝑙𝑙𝑖𝑖𝑙𝑙 𝑖𝑖→∞ 𝜀𝜀′ ( 𝜔𝜔 ) .
The Kramers/Kronig relat ions describe the relatio n between the real and the ima ginary part of
a complex compliance obtained from one - sided Fo urier transforma tion . T he rel ati on b etween
𝜀𝜀′ ( 𝜔𝜔 ) and 𝜀𝜀 ′′ ( 𝜔𝜔 ) is de scribed the Kramers/K ronig rela tions is

28

𝜀𝜀 ′ ( 𝜔𝜔 ) − 𝜀𝜀 ∞ = 1 𝜋𝜋 ∮ 𝜀𝜀 ′′ ( 𝜉𝜉 )
𝜉𝜉 −𝑖𝑖 𝑑𝑑𝑑𝑑

and
𝜀𝜀 ′′ ( 𝜔𝜔 ) = 1 𝜋𝜋 ∮ 𝜀𝜀 ′ ( 𝜉𝜉 )
𝜉𝜉 −𝑖𝑖 𝑑𝑑𝑑𝑑

(8)
An alys is o f Diel ectr ic Spect ra : Dielectric relaxation proces ses , due to t he fluctuations of
molecular dipoles, are ch aract eriz ed as a st ep - li ke d ecreas e o f th e real part 𝜀𝜀′ with inc reasing
frequen c y and a p eak in imaginary part 𝜀𝜀 ′′ . An illustr ation of a die lectric re lax ation pr ocess is gi v e n
for f requ enc y d ep end enc e of 𝜀𝜀 ′ and 𝜀𝜀 ′′ in F i gur e 9. Qua nti tat ive an al ysis of t he dielect ric rel ax at io n
processes is usually done using model functions in order to obtain information about the molecular
d y n amics ; particular l y to estimate the relax ati on r at e ( 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 ).

log ε ''
log ( ω / ω
max
)
ω
max
= 2 π f
max
8
∆ε = ε
s
- ε
8
ε
ε '
ε
s

Figure 9 . Freq uency dep endence of t he real part , 𝜀𝜀′ , and the imagin ar y part , 𝜀𝜀 ′′ , of the complex dielectric fu nct ion
giv e n for dielectric relaxation process.

Debye - Beh avior : D e b ye developed the fi rst theory f or die lectric re lax ation . 109F
110 This theo r y
assumes that the chang e in pol arization is proporti onal to its actu al value , 110F
111 a nd t ime dependenc e
of a di elect ri c proc ess is giv en as
𝑑𝑑𝑃𝑃 ( 𝑡𝑡 )
𝑑𝑑𝑡𝑡 = − 1
𝜏𝜏 𝐷𝐷 𝑃𝑃 ( 𝑡𝑡 )

(9)

29

where 𝜏𝜏 𝐷𝐷 = 1
2𝜋𝜋𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 = 1
𝑖𝑖 𝑚𝑚𝑚𝑚𝑚𝑚 i s th e relax at ion time of a diel ectri c pro cess . Fr om eqn. (9), a dielec tr ic
function in the freque nc y domain is deri ved . The function is called the Deby e function, which is
given fo r 𝜀𝜀 ∗ ( 𝜔𝜔 )
𝜀𝜀 ∗ ( 𝜔𝜔 ) = 𝜀𝜀 ′ ( 𝜔𝜔 ) − 𝑖𝑖 𝜀𝜀 ′′ ( 𝜔𝜔 ) = 𝜀𝜀 ∞ + ∆𝜀𝜀
1 + 𝑖𝑖 𝜔𝜔𝜏𝜏 𝐷𝐷

(10)
where ∆𝜀𝜀 i s t he di electr i c st ren gth, whi ch is eq ual t o the s tep h ei ght o f th e r eal part o f a rel ax ati on
process or the area under the dielectric loss peak.
Non - Deby e - Beh avi or: In practi c e, th e rel ax ati on p ro cesses o f the sy st ems h aving amorphous
regions in their struct ures , e.g. amorphous pol ymers and LC s , are broader tha n what it is pre dicted
by Deb y e function given in eqn. (10) . Theref ore, th e Deb y e f uncti on i s insufficient t o des crib e
thes e proc ess es hav in g a so - call ed no n - D e b ye -behavior.
The bro adeni n g of a s ymm etri c relax at ion peak, w ith respect to the Deb ye on e, is descri bed b y
Cole/Cole function (CC -function) 11 1F
112
𝜀𝜀 ∗ ( 𝜔𝜔 ) = 𝜀𝜀 ′ ( 𝜔𝜔 ) − 𝑖𝑖 𝜀𝜀 ′′ ( 𝜔𝜔 ) = 𝜀𝜀 ∞ + ∆𝜀𝜀
( 1 + 𝑖𝑖 𝜔𝜔𝜏𝜏 𝐶𝐶𝐶𝐶 ) 𝛽𝛽

(11)
where 𝛽𝛽 d escri be th e s y m m etri c broad en in g of the rel ax atio n peak wit h resp ect t o t he Deb ye one.
𝛽𝛽 has its value within the boundary condition of 0 < 𝛽𝛽 ≤ 1 . 𝜏𝜏 𝐶𝐶𝐶𝐶 is the relaxation time.
In addition to the symmetric br oad ening, the broadening of a relaxation peak can also be
asymmetr i c, which can b e defined by the Cole/Davidson function (CD -fun ction) 112F
113 ,
113F
114
𝜀𝜀 ∗ ( 𝜔𝜔 ) = 𝜀𝜀 ′ ( 𝜔𝜔 ) − 𝑖𝑖 𝜀𝜀 ′′ ( 𝜔𝜔 ) = 𝜀𝜀 ∞ + ∆𝜀𝜀
( 1 + 𝑖𝑖 𝜔𝜔𝜏𝜏 𝐶𝐶𝐷𝐷 ) 𝛾𝛾

(12)

30

where γ descri be th e a s y m m etri c broad eni n g of th e relax at io n peak w ith res p ect t o th e D eb ye one.
γ has its value within the boundary condition of 0 < 𝛾𝛾 ≤ 1 . 𝜏𝜏 𝐶𝐶𝐷𝐷 is the r elaxation time.
In m ost of the c ases, non - Deb ye rel ax at ion pro cesses can b e w ell - des crib ed b y
Havr ilian/ Nega mi funct ion (HN -function). HN -function c ons iders both s y mm etric and
as y m met ri c bro adeni n g of a rel ax atio n peak , th erefo re, i t is the m os t generali zed form of th e Deb ye
function among t he model functions. HN-function reads
𝜀𝜀 ∗ ( 𝜔𝜔 ) = 𝜀𝜀 ′ ( 𝜔𝜔 ) − 𝑖𝑖 𝜀𝜀 ′′ ( 𝜔𝜔 ) = 𝜀𝜀 ∞ + ∆𝜀𝜀
( 1 + ( 𝑖𝑖 𝜔𝜔𝜏𝜏 𝐻𝐻𝐻𝐻 ) 𝛽𝛽 ) 𝛾𝛾

(13)
where t he fra cti onal pa ram eters 𝛽𝛽 and 𝛾𝛾 ( 0 < 𝛽𝛽 ; 𝛽𝛽𝛾𝛾 ≤ 1 ) descr ib e t he s y m met ric and as ymm etric
broadening of the relax ation spectrum with respect to the Deby e one. 𝜏𝜏 𝐻𝐻𝐻𝐻 den ot es th e relax at ion
time co rresponding to the freq u ency of m aximal die lectric loss 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 .
The real and the imaginary p arts of the HN-function are given in eqn. (14) and (15).
𝜀𝜀 ′ 𝐻𝐻𝐻𝐻 = 𝜀𝜀 ∞ + ∆𝜀𝜀 � 1 + 2( 𝜔𝜔 𝜏𝜏 𝐻𝐻𝐻𝐻 ) 𝛽𝛽 𝑐𝑐𝑙𝑙𝑐𝑐 � 𝛽𝛽𝜋𝜋
2 � + ( 𝜔𝜔 𝜏𝜏 𝐻𝐻𝐻𝐻 ) 2𝛽𝛽 � −𝛾𝛾 / 2 𝑐𝑐𝑙𝑙𝑐𝑐 [ 𝛾𝛾𝛾𝛾 ( 𝜔𝜔 ) ]

(14)

𝜀𝜀 ′′ 𝐻𝐻𝐻𝐻 = ∆𝜀𝜀 � 1 + 2( 𝜔𝜔 𝜏𝜏 𝐻𝐻𝐻𝐻 ) 𝛽𝛽 𝑐𝑐𝑙𝑙𝑐𝑐 � 𝛽𝛽𝜋𝜋
2 � + ( 𝜔𝜔 𝜏𝜏 𝐻𝐻𝐻𝐻 ) 2𝛽𝛽 � −𝛾𝛾 / 2 𝑐𝑐𝑖𝑖 𝑙𝑙 [ 𝛾𝛾𝛾𝛾 ( 𝜔𝜔 ) ]

(15)
where 𝛾𝛾 ( 𝜔𝜔 ) is def ined as
𝛾𝛾 ( 𝜔𝜔 ) = 𝑎𝑎𝑎𝑎𝑐𝑐𝑡𝑡𝑎𝑎𝑙𝑙 � 𝑐𝑐𝑖𝑖 𝑙𝑙 � 𝛽𝛽𝜋𝜋
2 �
( 𝜔𝜔 𝜏𝜏 𝐻𝐻𝐻𝐻 ) −𝛽𝛽 + 𝑐𝑐𝑙𝑙𝑐𝑐 � 𝛽𝛽𝜋𝜋
2 � �

(16)
The HN func ti on can be considered a s a combinat ion of the Deby e function , the CC - and the
CD -func t ion. In cas e o f 𝛽𝛽 =1 and 𝛾𝛾 =1, HN - fun ction is reduced to D eb y e function (eqn. (10) ); in
case of 𝛽𝛽 ≠1 and 𝛾𝛾 =1, comes to be CC - function (e qn. (11) ); and i n case of 𝛽𝛽 =1 a nd 𝛾𝛾 ≠1, gives

31

CD - func t ion (eqn. (12) ). Theref or e, th e HN - funct ion is mostly used to describe the dielectric
relaxation peaks having bot h Deb y e -behavior and no n- D e b ye -behavior. Th us, in the cou rse of this
study, all relax at ion pro cess es h ave b een an al y z ed b y fittin g HN -function to the die le ctric loss
spect ra given in eqn. (17) . Eqn. (17) takes into account the conductivity contribution, which is
often observed in the diel ectr ic lo ss s pe ctra o f m at erial s hav in g hi gh - char ge car rier m obi li t y such
as C LC s , during t he data analy si s using HN -function. 𝜀𝜀 ′′ = 𝜎𝜎
𝑖𝑖 𝑠𝑠 𝜀𝜀 0 des cribes th e conductivity
contribution to the dielect ric loss, whe re σ is co nn ected t o th e DC conductivit y, s is a parameter to
model non - Ohmic e ffects . Fo r Ohmic -behavior, s is equal to 1, and s<1 holds for a
non- Ohmic -beh avior.
𝜀𝜀 ′′ 𝐹𝐹𝑖𝑖𝑖𝑖 _ 𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹 = 𝜀𝜀 ′′ 𝐻𝐻𝐻𝐻 ( 𝜔𝜔 ) + 𝜎𝜎
𝜔𝜔 𝑠𝑠 𝜀𝜀 0

(17)
Furthermo re, Wübbenhorst and van Turnhout de veloped the derivative- based an al ysis
technique called “conduction - fre e” di el ectri c los s ( 𝜀𝜀 𝑑𝑑𝑑𝑑𝑑𝑑𝑖𝑖𝑑𝑑
′′ ) spe ctra anal y s is in o rder to eliminate
Ohmic conductivity c ont ribution t o dielectric spectra. 11 4F
115 It is based on the idea of 𝜀𝜀 ′ and 𝜀𝜀 ′′ carr y
the same information due to the K ramers/Kronig relations. This is a powerf ul wa y of anal yzing
the d ata for rel ativel y st rong c ondu c ting die l ectric mate rials, whic h eliminates th e conductio n
contribution. 𝜀𝜀 𝑑𝑑𝑑𝑑𝑑𝑑𝑖𝑖 𝑑𝑑
′′ is obtained by taking the first derivati ve of the real part ( 𝜀𝜀′ ) with r espect to the
logar i thm of the frequency . For a Debye function it holds
𝜀𝜀 𝑑𝑑𝑑𝑑 𝑑𝑑 𝑖𝑖𝑑𝑑
′′ = − 𝜋𝜋 2 𝜕𝜕 𝜀𝜀 ′
𝜕𝜕𝑙𝑙𝑙𝑙𝜔𝜔 ≈ 𝜀𝜀 ′′

(18)
From eqn. (18) it is concluded that 𝜀𝜀 𝑑𝑑𝑑𝑑𝑑𝑑 𝑖𝑖𝑑𝑑
′′ dis pla ys a peak l ik e the d ielect ric l oss . Bec ause o f the
square in eqn. (18) t he p eak in 𝜀𝜀 𝑑𝑑𝑑𝑑𝑑𝑑𝑖𝑖𝑑𝑑
′′ is much na rrower than tha t in the dielec tric loss. Moreover,

32

Ohmic - conduction is r emoved, because in that case 𝜀𝜀 ′ is independent of frequenc y. For the
HN -function, one obtains
− 𝜕𝜕 𝜀𝜀 ′ 𝐻𝐻𝐻𝐻
𝜕𝜕𝑙𝑙𝑙𝑙𝜔𝜔 = 𝛽𝛽𝛾𝛾 ∆ 𝜀𝜀 𝐻𝐻𝐻𝐻 ( 𝜔𝜔 𝜏𝜏 𝐻𝐻𝐻𝐻 ) 𝛽𝛽 𝑐𝑐𝑙𝑙𝑐𝑐 � 𝛽𝛽𝜋𝜋
2 − (1 + 𝛾𝛾 ) 𝛾𝛾 ( 𝜔𝜔 ) �
� 1 + 2 ( 𝜔𝜔 𝜏𝜏 𝐻𝐻𝐻𝐻 ) 𝛽𝛽 𝑐𝑐 𝑙𝑙𝑐𝑐 � 𝛽𝛽𝜋𝜋
2 � + ( 𝜔𝜔 𝜏𝜏 𝐻𝐻𝐻𝐻 ) 2𝛽𝛽 �

1+𝛾𝛾
2

(19)
where 𝛾𝛾 ( 𝜔𝜔 ) is given in e qn. ( 16 ).
Conductivity Contributi on: The relationship between the complex dielectric function ε ∗ and
the complex conductivit y σ ∗ is given b y
𝜎𝜎 ∗ ( 𝜔𝜔 ) = 𝜎𝜎 ′ ( 𝜔𝜔 ) + 𝑖𝑖 𝜎𝜎 ′′ ( 𝜔𝜔 ) = 𝑖𝑖𝜔𝜔 𝜀𝜀 0 𝜀𝜀 ∗ ( 𝜔𝜔 )

(20)
where 𝜎𝜎 ′ and 𝜎𝜎 ′′ are the r eal a nd im aginar y part of th e co mpl ex cond ucti vi t y σ ∗ . 𝜎𝜎 ′ and 𝜎𝜎 ′′ are
defin ed as
𝜎𝜎 ′ ( 𝜔𝜔 ) = 𝜔𝜔 𝜀𝜀 0 𝜀𝜀 ′′ ( 𝜔𝜔 )

(21)

and
𝜎𝜎 ′′ ( 𝜔𝜔 ) = 𝜔𝜔 𝜀𝜀 0 𝜀𝜀′ ( 𝜔𝜔 )

(22)

The frequency dependence of the real part of the complex conductivit y 𝜎𝜎 ′ , given in Fi gu r e 10,
shows the ty pic al behavior of semiconducting di sordered m aterials s uch as i oni c glass es, i on
conducting polymers, and electron - conducting conjugated pol y mers. 99 A t hi gh f requ enci es
(dispersive reg i on) , 𝜎𝜎 ′ decreases with decreasing fre quenc y with a power la w down to a
chara cteri sti c fr equenc y 𝑓𝑓 𝐹𝐹 characterizing the onset of dispersion. A plateau value c orr esponds to
the DC conductivity ( 𝜎𝜎 𝐷𝐷𝐶𝐶 ) is obs erved fo r freq uen cies at 𝑓𝑓 < 𝑓𝑓 𝐹𝐹 . For hi gher temp erat ures , elect rode
polarization shows up at lower frequencies b y a fu rt her de cre ase of 𝜎𝜎 ′ with de creasin g frequ enc y .
Electrode polarization is an unwanted effect du e to a p artial blocking of char g e carr iers at the
ex ternal elect rodes . 99

33

The frequ en c y d ep end e nce of 𝜎𝜎 ´ ( 𝑓𝑓 ) can be appro x imated b y the wel l - kno wn power law
introduced by Jonscher
σ ´ ( f ) = σ DC � 1 + � f
f c � n �

(23)
besides other models. 99 The exponent n is found to be between 0.5 and 1. f c is relate d to 𝜎𝜎 𝐷𝐷𝐶𝐶 b y
the e mpirical B arton - Nakajima - Nam ikaw a rel ati o n (BNN) 𝜎𝜎 𝐷𝐷𝐶𝐶 ~ 𝑓𝑓 𝐹𝐹 . 115F
116 ,
116F
117 ,
117F
118 By fittin g t he
Jonscher-equation (eqn. (23)), the 𝜎𝜎 𝐷𝐷𝐶𝐶 is es ti mated and i ts t emp erature d ep end ence i s ob tain ed.

σ
DC
log σ '
log f
plateau region
dispersive region
electrode polarizatin region

Figure 10 . T ypical f requency dependence of the real pa rt of the complex conductivit y 𝜎𝜎 ′ for sem icondu cting
disordered materials

. Dashed - dotte d li nes i ndi cat e t he pl ate a u c or re sp ond ing t o t he DC c o nd uc ti vit y.

3.1.2. Specific Heat Spectr oscopy
Speci fic h eat spe ctr oscop y (S HS) is us ed to inv esti gat e glass d ynam ics i n th e f req uen c y ran ge
from 10 -6 Hz t o 10 5 Hz by emplo y in g different techniques for the dif ferent frequency ranges. SHS
is carried o ut b y di ff erent i al AC - chip calo rimetr y i n the frequenc y range fro m 10 -2 Hz to 10 5 kHz ,
temp eratur e m odul ated DS C (TMDS C) i n the freque nc y range from 10 -6 Hz to 10 2 Hz , and fast

34

scanni ng calor imet r y em pl o y i n g Step Scan ap pro a ch (see Section 3.2.3 f or the St epScan appr oa ch)
in the freque n c y ra n ge from 10 -1 Hz to 10 4 Hz . 118F
119
SHS is a power ful t echnique to stud y the gla s s y dyna mi cs from t he pers p ectiv e of ent hal p y
fluctuations. I n S HS, when heat is not simultaneou sl y distributed in a material under investigation,
tim e depen denc y o ccurs . 11 9F
120 This results in time and freque n c y depe n d en c e of the change of
temp eratur e or he at in the m ateri al. In cons e qu ence, h eat cap acit y of t he mat erial und er
investigation bec om es frequenc y - d ependent. Therefore, the frequenc y - depende nt heat capacity
obtained from SHS measurements can b e compared to th e comple x dielectr i c permittivity obtained
from B DS measureme nt. 119
Similar to B DS, SHS ca n be also described in th e framework of LR T . 107 , 108 To understand
principles of SHS, ther modynamic relation between specific he at and enthalp y should be
consi dered . Thermodyn a mic rela x ation between c onstant pressure specific heat, 𝑐𝑐 𝑃𝑃 , and the change
in s pecifi c enth alp y of a s ystem, 𝜕𝜕𝜕𝜕 , is given in e qn. (24) 120F
121
𝑐𝑐 𝑃𝑃 = � 𝜕𝜕𝜕𝜕
𝜕𝜕𝑅𝑅 � 𝑃𝑃

(24)
In this case of S HS in t he framewo rk o f LRT, a peri odi c tem peratu re h av ing a sm all amplitude ,
𝑅𝑅 ( 𝑡𝑡 ) = 𝑅𝑅 0 + 𝐴𝐴 𝑇𝑇 sin ( 𝜔𝜔𝑡𝑡 ) ( where 𝐴𝐴 𝑇𝑇 is amplitude o f the applied t emperat ur e perturbation), is
ex ternal l y applied as d is t urban ce t o a s y st em un d er in vest i gation . Consequentl y, the r espon se o f
the system to this disturba nce is the phase -shifted en thal p y (see F i gu r e 11), 121F
122 where eqn. (24)
becom es
𝜕𝜕𝜕𝜕 ( 𝑡𝑡 ) = � 𝑑𝑑 𝑐𝑐 𝑃𝑃 ( 𝑡𝑡 − 𝑡𝑡′ )
𝑑𝑑𝑡𝑡
𝑖𝑖
−∞ 𝜕𝜕𝑅𝑅 ( 𝑡𝑡′ ) 𝑑𝑑𝑡𝑡′

(25)
W he n this equation is Fourier transf orm ed, it would y ie ld

35

𝜕𝜕 ( 𝜔𝜔 ) = 𝑐𝑐 𝑃𝑃 ∗ ( 𝜔𝜔 ) 𝑅𝑅 ( 𝜔𝜔 )

(26)

w here 𝑐𝑐 𝑃𝑃 ∗ ( 𝜔𝜔 ) = 𝑐𝑐 𝑃𝑃 ′ ( 𝜔𝜔 ) − 𝑖𝑖 𝑐𝑐 𝑃𝑃 ′′ ( 𝜔𝜔 ) is the complex s pecific heat and 𝛿𝛿 i s th e phase shi ft , where
tan 𝛿𝛿 = 𝐹𝐹 𝑃𝑃 ′′
𝐹𝐹 𝑃𝑃 ′ . 𝑐𝑐 𝑃𝑃 ′ ( 𝜔𝜔 ) is the real part o f th e comp lex sp ecifi c heat, w hereas 𝑐𝑐 𝑃𝑃 ′′ ( 𝜔𝜔 ) is the imag inar y
part o f the co mpl ex speci fic heat .

Figure 11 . ( a) Schemat ic rep resentation of LR T for the case of S HS. (b) Schem atic relatio nships between t he tim e
dependence of the periodic electric field E(t) and that of the period ic phase

-
shifted po larizatio n P(t) in the fra mework
of LRT for the case of SH S.

Fourier transformation can be applied to o btain the relationship of 𝑐𝑐 𝑃𝑃 ∗ ( 𝜔𝜔 ) to the
time -depe ndent diele ctric function 𝑐𝑐 𝑃𝑃 ( 𝑡𝑡 ) 123
𝑐𝑐 𝑃𝑃 ∗ ( 𝜔𝜔 ) = 𝑐𝑐 𝑃𝑃 ′ ( 𝜔𝜔 ) − 𝑖𝑖 𝑐𝑐 𝑃𝑃 ′′ ( 𝜔𝜔 ) = 𝑐𝑐 𝑃𝑃 ∞ − 𝑖𝑖𝜔𝜔 � 𝑑𝑑 𝑐𝑐 𝑃𝑃 ( 𝑡𝑡 )
𝑑𝑑𝑡𝑡 𝑒𝑒 − 𝑖𝑖𝑖𝑖𝑖𝑖 𝑑𝑑𝑡𝑡
∞
0

(27)
where 𝑐𝑐 𝑃𝑃 ∞ rep res ents th e real p art 𝑐𝑐 𝑃𝑃 ′ in the limit of 𝑐𝑐 𝑃𝑃 ∞ = lim ω →∞ 𝑐𝑐 𝑃𝑃 ′ ( ω ) .
3.2 Exp erim ental Secti o n
3.2.1. Therm og ravi metric Analysis
TGA measurements were carried out b y a Seiko TG/DTA 220. A heating rate of 10 K min -1
was app lied from 303 K to 1073 K, under s ynthe t ic air havi n g a fl ow rat e o f 200 ml min -1 .
(b)

(a)

36

3.2.2. Fourier Trans f orm Inf rared Sp ect rosco p y
The atten uated t otal r eflect ion Fou rier t r ansf orm infr ared spect ro sc op y (ATR - F T IR )
measu rement s wer e pe rf ormed for the empt y u nmodified and the modified me mbranes . Th e
measu rement s were c arried out at room temperature using a Thermo Scientific Nicolet 6700 FTIR
wit h a Sm art Orb it diamon d ATR accesso r y. The number of acc umul ated scans was 32 with a
resolution of 4 cm -1 in t he wavenu mb er r an ge fro m 4000 cm -1 to 400 cm -1 .
3.2.3. Dif f erenti al S cann in g Cal ori metry
Conventional diffe rential scann ing calorime tr y ( DSC ) measu rement w as carr ied o ut b y a
Perkin Elmer DSC 8500. The sample (ca. 6 mg) was enc apsulat ed in a standard 50 µl alu minum
pan. The sample was m easured with a heating/cooling rate of 10 K min -1 . A c r yofill LN 2 s y stem
from P erkin El mer was us ed to control th e tem per ature. Nitroge n w as us ed as a pu rge gas at a flo w
rate of 20 ml min -1 for t he measurements down to 173 K. In addition to nitrogen, helium was also
used as a purge gas at a flow r ate of 20 ml min -1 for th e m easur em ents down to 103 K. One
heati ng/ cooling cycle followed by a sec ond h eati ng run was employed. The second heating and
the cooling r uns w ere used to determine the phase tra nsit ions tem perature s. A b aseline
measureme nt was conducted b y m easuring an empt y 50 µ l aluminum pan under the same
con diti ons. The obtained baseline was subtract ed from the data measured for the s ample.
Moreover, the calibration of the DS C w as ch ec ked be fore th e m easur e ment b y me asuri n g an
indium standard.
3.3.4. Polariz i ng Optica l Microscopy
The polarizing optical micr os c o p y ( POM) measurements were carried out by a Zeiss Axioskop
Scope A1 optical microscope, with crossed polariz ers, connected to a L ink am THMS600 he ating

37

stag e. The stage w as equipped with a liquid nitro gen d ewar allow in g prec ise control of heating
and cooling rates.
A comme r cially available IT O - coate d liquid crysta lline cell was us ed for the POM
investigations. The liquid cr ystalline ce l ls, having square (10 mm x 10 m m) patterned I T O - co ated
electrode s and an average cell gap of 4µm, were purchased from Instec, Inc. (Colorado, USA). I t
was c apillary filled w ith HAT 6 in the Is o ph as e at 383 K b y placin g a sm al l am oun t of s ampl e to
the fro nt gate o f the cel l . Th ree heat in g/coo lin g c y c l es in the t emp eratur e ran ge from 350 K t o
383 K, with a heating and cooling rate of 1 K min -1 , wer e appl ied d urin g th e P OM m easurem ent s
for HAT6 in the liqu id cry s talline ce ll.
For the POM investigations on the dipole func ti onalized tripheny l ene - based D LCs , the
samples were prepared on glass slides and studied usi ng an Ol y mpus B X50 polarizi n g micros cop e
which is combined with a Linkam LTS350 heating stage. Pictures of the te xt ures wer e taken wit h
a SC35 Ty pe 12 camera from Ol y mpus. T hese m eas uremen ts regard in g the POM investigation of
the d ipole functionalized tripheny l enes we re p erf ormed b y Prof. Sabine Laschat’s group in the
Unive rsit y o f Stuttga rt.
3.3.5. X- ray Sca tteri ng
Lon g - range ordering of unm odified and modified AAO membranes as well as that of HAT 6
confined AAO m embranes with 38 n m diamet er pores was studied b y small angle X - r a y s cat teri n g
(SAXS) in the “MAUS”: a he avil y customized Xeuss 2.0 (Xenocs, Fra nc e). Here, MAUS st ands
for the s o - called abbreviation of the XRD setup use d: m ulti - scal e anal y z e r fo r ul trafi ne st ructu res .
X- ra y s ar e generat ed fro m a micro fo cus X - ra y tube with a copper targe t, followed by a multilay er
optic to parallelize and m onochromatize the X - ra y beam to a wavele n gth of 0.154 nm. The detector

38

consists of an in - vacuum motorized Eig er 1M, for this investigation placed a t distances of 208,
558, and 1258 mm from t he sample. After corre ction, the data from the diffe rent distances are
combine d into a single curve . Th e space betw e en the star t o f the collimatio n until the detector is a
continuous, uninterrupted vacuum to reduce bac kground. The membranes (discs) were mounted
wit h th eir su rface pe rpen di cul ar to t he beam in t he evacu ated s ampl e cham ber. The res ult in g data
has been processed using the DAWN soft ware package 123F
124 ,
124F
125 w ith the following proc essing ste ps
in order: masking, correction for counting time, dark - current, transmission, primar y beam flux,
background ( no s ample in the beam), f l at - field, polarization and solid a ngle, followed by azimut hal
averag i ng. The data has not been scaled to absolute units. P hoton count ing unce rtai nti es wer e
estimate d from the r aw image, and propagated throug h t he correction steps. For the alignment
experiment, the membrane was held upri ght between two LEGO bricks, on t op of a
Ph y sik Instrumente H811.I 2 V hexapod. 200 second exposures were ta ken at various tilt a ngles, to
seek the tilt ang l e that w oul d produce a radiall y i sotropic pattern. The m easurem ents and t he
simulations were perf o rmed b y D r. Brian R ich ard Pauw an d Dr. Glen J aco b Sm ales fro m
Bundesa ns talt für Materialforschung und - prüfu n g (BAM).
The d ipol e functionalized triphen y l enes were also s tudied using S AXS and W AXS. The
samp les were pla ced in mark tubes from Hil genberg (diameter of 0.7 mm) and sealed b y melting.
X- ra y po wd er exp erime nt s were perfo rmed b y a B ru ker A XS Nan os tar C di ffracto mete r
employing monochroma t ic Ni - filtere d Cu K α radia t ion ( λ = 1.5418 Å). A HI - STAR - det ector f rom
Bruker was use d fo r recording and calibrated by silver behenate at 298 K. The diffraction image s
were pro cess ed b y S AX S - so ftware from Bruke r, an d th e diff ractio n pat tern s were an al y z ed b y
Datasq ueez e S oft war e an d Ori gin. The meas u rem ents wer e p erfo rmed b y Pro f. S abine Las chat ’s
group in the University of Stuttgar t.

39

3.3.6. Broa db an d Di electri c Sp ect roscop y
The di elect ric pro p erti es of sam pl es were m easu r ed in the freq uenc y r an ge from 10 − 1 Hz to
10 9 Hz using broadband dielectric spectroscop y ( BDS ) . In BDS m easu remen ts , th e com pl ex
diele ctric function o f a capacitor f illed with a mater ial under investigation is ex press ed as 100
𝜀𝜀 ∗ ( 𝜔𝜔 ) = 𝜀𝜀 ′ ( 𝜔𝜔 ) − 𝑖𝑖 𝜀𝜀 ′′ ( 𝜔𝜔 ) = 𝐶𝐶 ∗ ( 𝜔𝜔 )
𝐶𝐶 0

(28)
where 𝐶𝐶 ∗ ( 𝜔𝜔 ) repres ents the co m plex cap acit ance of t he capacit or fi lled wit h th e mat erial and 𝐶𝐶 0
is the vacuum cap aci tan ce of t he arr an gement o f t he emp t y cap aci tor . 𝜀𝜀 ∗ ( 𝜔𝜔 ) can be der i ved b y
measu rin g the co mpl ex im pedance, 𝑍𝑍 ∗ ( 𝜔𝜔 ) , of the sample
𝜀𝜀 ∗ ( 𝜔𝜔 ) = 𝐽𝐽 ∗ ( 𝜔𝜔 )
𝑖𝑖𝜔𝜔 𝜀𝜀 0 𝐸𝐸 ∗ ( 𝜔𝜔 ) = 1
𝑖𝑖𝜔𝜔 𝑍𝑍 ∗ ( 𝜔𝜔 ) 𝐶𝐶 0

(29)
where 𝐽𝐽 ∗ ( 𝜔𝜔 ) is the complex current densit y .
Meas urem ent of Bulk Samples: For bulk samples, i n the frequ en c y ran ge f ro m 10 − 1 H z t o
10 6 Hz, a high - re sol ution ALPHA anal y z er (Novocontrol, Montabaur, Germany) including a
samp le ho lder wi th an a c ti ve sam ple h ead w as use d. Isot hermal frequen c y s cans w er e c arri ed ou t
temperatures down to 133 K. Samples were first h eated to a temperature higher than their clear in g
temp eratur es (T > T C olh - Iso ) , and then cooled to 133 K with a cooling r ate of 5 K min -1 to define a
specific ther m al histor y. One hea ti ng/cooling cy cl e followed b y a second heating run was
empl o y ed i n the temperature range from 133 K to T ≈ T Colh - Is o – 10 K. In t his temp eratu re ran g e,
the s ampl e t emp eratu re w as in cr eased (h eat in g run ) and de creas ed (cooling run) with a n incr emen t
of 2 K upon heating/cooling. When t he sam ple tem peratu re i s s tabi li zed at the set tem peratu re,
i sot hermal frequ enc y sc a ns were ap pli ed i n th is t emper ature ran ge .

40

From 10 6 Hz to 10 9 Hz, the bulk meas u rement s w ere p e rfo rmed usin g a co ax ial reflect omet er
based on an Agil ent E 49 91A R F im pedan ce an al yz er. Th e samp le was mod el ed as i nte gral p art of
the inner conductor. For details see ref . 100. Th e measu rement s w ere als o carri ed ou t i sot hermal l y .
For both measurements performed at different frequenc y w i ndows , th e s am ples wer e prep ared
between t wo di sk - shaped gold - pl ated b rass el ect rodes wit h a diam et er o f 10 m m (p aral lel pl ate
ge om etr y). A spacing of 50 μm was m aintained by fused si lica spacers. For bot h measurement
setup, the tempera t ure of the sample was controlled by a Qu atro Novocontrol temperature
controller with nitrog en a s a heating a gent providing a temperature stabilit y better tha n 0.1 K. For
detai ls s ee re f .s 99 and 1 00.
Meas urem ent of the Sa m ples for the Inv estigation of a CLC U nder Conf inement : Th e
measu rement s of H AT6 confined into nanochannels of the membranes were carried out using a
hi gh -resolution A L P HA anal y ze r (Novocontrol, Montabaur, Germany) including a sa m ple holder
wit h an act ive s ampl e head . T he tem peratu re o f the s ampl e was al so cont roll ed b y t he Qu atr o
Nov ocontrol temperature controller with nitroge n as a heating agent. The meas urem ent s were al so
perf ormed in pa r allel pla te geometry . This means that the disk - shap ed sam ples were pl aced
between two gold - plated brass elect rod es wi th a d iamet er of 1 0 mm or 15 m m depending on the
out er diam eter of t he me m branes . Sp acin g b etwee n el ectrod es was d efi ned b y the thi ckn ess of t h e
membranes. B ulk H AT6 meas urem ents we re cond uct ed us in g the liquid cry stalline cell p urchase d
from I nste c, Inc. . Th e cel l was c apillary f illed wit h HAT6 in the Is o phas e at 383 K b y pl acing a
small amo unt of sample to the front ga te of the cell.
For conf ined HAT 6 , t he complex die lectric pe r mittivit y, 𝜀𝜀 ∗ , w as measu red b y t emp eratur e
scans wit h a h eati n g and co oli ng r ate of 1 K min -1 at a constant frequenc y of 35 kHz. The r eason

41

of running measurement at 35 kHz is explained in detail in Section 5.3 . Three heating/cooling
cy c les, in the temperature range f rom 340 K to 383 K for smaller pore siz es (d < 34 nm ) a nd t hat
from 350 K to 383 K for the larger pore si zes (d > 34 nm), w ere employed to probe all samples.
Similarly , three heating/cooling c y cl es were applied for HAT6 in the liquid c r ysta lline cell in th e
temp eratur e ran g e from 3 5 0 K to 383 K.
3.3.7. Sp ecif ic H eat S pectroscop y
Speci fic h eat spect r oscop y (SHS) w as carr ied o ut b y differ ent ial AC - chip calorime tr y 12 5F
126 and
temp eratur e m odul ated DS C (TMDS C).
Diff erential AC -C h i p C alorim etr y: Diffe rential AC - chip c alorimetry is based on an approach
that i s obt ained b y m easuring a chip wit h a samp l e again st an empt y chi p in a diff eren tial s et -up.
Most of the other calorimetric techniques is also based on the di ffere nt ial approac h . This app roach
minimize s t he heat cap aci t y c ont ribution originati ng fr om the empt y chip itself. The differential
approac h brin gs two orders of m agnitude increase in the sen sitivit y (≈ pJ K -1 ) for this technique
comp ared to an AC - chip calorimetry (non - differential approach ). In this technique, an alternatin g
curre nt (AC) is applied t o the material under study, and period ic h eat f lo w i s meas ured as t he
respond of the material.
The nanocalorimeter chips XEN 39390, purchased from Xensor Integration and shown
in Fi gu re 12 , we re emplo ye d to c arry out the A C - chi p calo rimet r y meas u rement s. The chip h as
two four - wir e heaters loca ted in the middle of a free - stan din g 1 µm thick silicon nitr ide (SiN)
membrane. The heated area of about 30 µm x 30 µ m is in the center of thin S iN memb ran e.
Six -c oupl e thermopile, integ r ated in the heated area, senses the temperature. 12 6F
127

42

Figure 12 . Pictu res of ( a) XEN 39390A C - chip sensor, (b) SiN m e mbrane fixed on a rectangular s il ico n nitride
subst r ate, and (c)

The heated area o f about 30 µm x 30 µm in the center of the rectangular silicon substrate.
T he
p ictures were adapted from ref . 127 .

In t he diff eren tial app ro ach , two identica l chips ar e ass umed . 126 In this approx imation, the heat
capa cit y of th e samp le C s is given by
𝐶𝐶 𝑠𝑠 = 𝑖𝑖𝜔𝜔 𝐶𝐶 𝑑𝑑𝑓𝑓𝑓𝑓 ( ∆𝑈𝑈 − ∆𝑈𝑈 0 )
𝑃𝑃 0 𝑆𝑆

(30)
where S is the sensitivity of the thermopile, and P 0 is the applied heating power. C eff = C 0 + 𝐺𝐺
𝑖𝑖ω
denot es t he ef fecti ve h eat capa cit y of th e em pt y se ns or where 𝐺𝐺
𝑖𝑖ω is the he at lo ss to the surrounding
atmosphere. ∆ U is the c om plex differ ential ther mop ile sig nal for a n empt y and a sensor with a
sample, and ∆ U 0 is t he complex diffe rential voltage measured for two empty sensors. The
measu red comp lex di ffe renti al v olt age c an be cons idered as measu r e fo r the co mpl ex heat
capa cit y.
The AC - chip cal ori met r y measu rem ent s we re c arried o ut i n th e tem pe rature s c an mo de .
Temper atur e was r amp ed at a fi x ed m odulat ion frequen c y b y appl yin g a heat ing and cool in g rate
in the range be t ween 1.0 and 2.0 K min -1 depending on the pr o grammed frequenc y to ensure a
stationary state. A fter each heating and cooling runs the frequenc y was changed stepwise in the
ran ge of 1 Hz - 10 k Hz. To ensure a linear r egime, the amplitude of the temperature modulation
was set to be less than 0.25 K. 12 6 Further details can be found in re f. 126 . The AC - chip sensors for
(a)

(b)

(c)

43

the m easur emen t w er e p repar ed b y pl acin g a s ma ll amou nt o f a s ampl e on to the S iN m emb ran e
under an optica l microsc ope. After that, the sample wa s melted on the heated a rea.
Tem per atu re M odul ated D SC: Temp eratu re m odu lated DSC (TM DSC ) meas uremen ts a re
appl ied t o me asu re t he com plex h eat capa cit y besi des the to tal he at cap acit y . 128 T MD SC
measureme nt s were con ducted b y a Pe rkin Elmer DSC 8500 using the StepScan approach
(St epScan DSC – S SDSC). SS DSC is a special variant of TMDSC , which combines alternating
short heating and isotherm al steps. Here, the h eight and time of the isothe rmal step and the heating
rate b etw een the s teps ar e pr ed efined an d th e h eat - fl ow r ate resp ons e i s m eas ured (s ee Fi gur e 13).
The modulation frequenc y corresponds to the ti me of the isothermal ste p. Due to the periodic
pertu rbati on, the re al par t of t he com pl ex heat cap acit y of a s ystem (r elat e d to the rev ersin g heat
capa cit y 128 ) can b e ex t rac ted fr om t he rati o of t he area un d er the h eat - flow peak and height of the
temperature step. Four ie r anal y sis of the raw data is not absolutel y r equired. 12 7F
128 Calibration of th e
heat fl ow was performed with s y nthetic s apphire (α - Al 2 O 3 ) as a ref eren ce m aterial . S SDS C was
carr i ed out in the frequen cy range from 3.2 x 10 -3 Hz to 5.6 x 10 -2 Hz with a constant step height
of 1 K and the heating rates in t he range from 40 K min -1 t o120 K min - 1 .
F or the temperature contr ol, a c r yo fill LN2 sy stem from P erkin Elmer was u sed . Nit ro gen w as
used as a purge gas at a flow rate of 20 ml min - 1 for the mea surements down to 173 K, and helium
to reach the l ower temper atures down to 103 K.

44

Time
Heat Flow (Endo Up)
t
P

Temperature
A
T

Figure 13 . (a) Tem perat ure program appli ed for a SSDSC measuremen t . I t illustrate s the p red efined hei ght and ti me
of the isot her mal step

(A T and t p ) and the heating rate between the steps are used in th e temperature program . ( b
)
Measured heat

- flow rate respons e o f the material t o the appl i ed tem perature prog ra m given in F i gure 13 a.
3.3.8. Fast Scanning Calorimetr y
The g lass transition s detect ed us in g conven ti onal DS C w ere fu rt her i nv est igated t hrou gh fast
scanni ng calor imet r y (FS C) experi ment s allowin g heating rates from 10 K s -1 to 10000 K s -1 . FSC
measu rement s wer e pe rf ormed using a Mettler Toledo Flash DSC 1, which is a chip- based po wer
comp ensat ed differential c alorimetry . 1 19 ,
128F
129 MultiSTA R UFS 1 twin chip sensors, shown in F i gur e
14, were used fo r t he me asu rement s (fo r det ails s ee ref. 129F 130 ). Nitro gen was use d as a pur ge gas at
a flow r at e of 40 ml min -1 . A Huber TC100 intercooler was used to contr ol t he tem perat ur e.
(a)

(b)

45

Figure 14 . Sample area of the MultiSTAR UFS 1 twin chip sensor (a) before placing a sam p le at the heated area, (b)
after a sample was placed at t he heated area, and (c) after the placed sample was melted on the heated area. Fi gure
wa s ta ke n fr o m re f. 43 with pe r mission (see Sect ion 4.1 for t he perm issi on) .

“Conditioning” and “correction” pr o cedures given b y the m anufacture r w ere appl ied b ef or e
the m easurem ents . Th e s ampl es were p la ced at h eated ar ea ( Fi gure 14 b), an d th en mel ted at
temp eratur es abov e t heir cleari n g tem per atu res b y hea ti ng from room temp erature with a heating
rate of 500 K s -1 ( Fi gu r e 14 c). Th e meas u rement s were ca rried out b y heating the samp les from
178 K to T ≈ T Colh - Is o – 1 0 K with heating rates from 10 K s -1 to 10000 K s -1 . A cooling r un with a
rate of 1000 K s -1 w as ap p li ed pri or to ever y heati ng meas u remen t to ensu re t hat the s ampl es hav e
the same therma l histor y before a heating run.
3.3. Mate r ials
3.3.1. Triphenylene- Base d Discot ic Liquid Cryst als
Triphen y l ene- bas ed D LCs 2,3,6,7,10,11- hexakis[hex y lox y ] triphen y l en e ( HAT6 ) a nd
2,3,6,7,10,11- hexakis[pent y lox y ] triphen y lene ( H AT5 ) w ere purchased from S y nthon Chemicals
(B itterfeld, Germany , CAS -no.: 70351-86-9 for H AT6 , C AS - no.: 69079 -52 - 3 for HAT5 ) and used
as rec eived . Th e m olecu lar wei g h t of HAT6 wa s confirme d b y matrix - ass ist ed las er
desorption/ionization- time of flight (MAL D I - TOF) m easur ement . The m olec ul ar wei ght of HAT 6
was found to be 828.63 g m ol -1 b y M A LD I - TO F MS (see Appendix I , Fi gur e S 1 ), and it is in

46

agreem ent wit h its reported value 21 . A ccording to the producer, their pur it ie s are at least 98 %. At
room temperature, the ap pearan ce s of H AT5 and H AT6 are that of white cr y stals.
The chem ic al s truct ure s o f HAT 6 (sum formu la C 54 H 84 O 6 ) and HAT5 (sum formu la C 48 H 72 O 6 )
are shown in Fi gure 15 . Moreover, a schematic illustr ation of their molecular org a nization an d the
thermotropic phases is shown in Fi gu r e 2 for D L C s includin g HAT6 and HAT5 . At l ow
temp eratur es , both HAT6 and H AT5 form a C r y phase . Upon further heating from the Cry phase,
the y have a Col h m esophase. Wi th further hea ti ng from the Col h phase, t he y unde rgo a clearin g
trans ition to a more or less Is o liquid state .

Figure 15 . (a ) C hemic al struc ture of 2,3,6,7,1 0,11 - hexaki s [ hex ylo x y] tr ip hen yle ne ( H AT6 ). D

HAT6
is dia meter of
HAT6

m olecules, reported to be ca. 2.1 nm . 13 0F
131 Fi g ur e was take n/adapted from ref . 25 w it h per mission (s ee Chapt er
5
for the per mission) . (b) Ch e mical struc t ure of 2,3,6,7, 10,11 he xakis[ pentyloxy ] triph e ny lene ( HA T5 ).

In a ddit ion to the above -mentioned s y mmetrical t r i phen ylene - b as ed D LCs, a sel ected s eries of
dipole functionalized tripheny l ene - b ased D LC s were als o studied in this wor k , which are
pent apent y l ox y t ri phen y l en es car r ying eth y l gl y col at e ( SH U09 ), hexanoyl ( SHU10 ),
trifluo romethyl ( S HU11 ), and dieth ylenegl y col ( SHU12 ) unit s. The t ri phen ylen e d erivat ives ,
SHU09 - SHU12 , can be regarded as mono functionaliz ed derivatives of HAT 5 . The ch em ical
struct ures of t he tr iph en ylen e deriv ativ es are given i n Fi gur e 16. The monofunctionalized
(a)

(b)

47

trip hen ylene d erivat ives SHU09 - SHU12 wer e s ynthes iz ed b y Pro f. Sabine La sch at’s group in t h e
Unive rsit y o f Stuttga rt . The s y nt hesis of SHU09 - S H U12 is given in ref. 43.

Figure

16 . Chemi cal st r uc t ure s of t he m ono functiona lized triphen ylene derivati ves SH U09 - SHU 12 . Figur e was
ta ken
fro m r e f. 43 with per missio n (see Section 4.1 for th e perm ission ) .

All monofunctionalized tripheny len e derivatives ar e the rmal l y stabl e at l east u p to 533 K ,
determined using TGA (see Appendix I , Fi gu r e S 2 ).
3.3.2. Trip h enyl ene C row n E ther - Bas ed Di scoti c Liqu id Crys tal s
Trip hen ylene c row n eth er - based uns y mmetrical D LC s , term ed as KAL465 and KAL468 , w er e
studied. The s y nthesis of KAL465 and KAL468 was done by Prof. Sabine Laschat’s group in the
University of Stuttgart . The s y nthesis and the mes omorphic properties of th ese DLCs ar e given in
ref 131F 132 . Fi gu re 17 shows t he chemi cal st ructu res of t h e D LC s and a schematic illustr ation of their
molecular organization . The m olecu les of th e K AL compounds h ave a cen tral [1 5] crown - 5 with
two separate triphenylenes connected to each other through the central crown and alk y l ch ai ns
attach ed to th e tr iph en ylen es . This i s t he mai n di fferen ce b etwe en the triphenylene crown
ether - b ased D LCs and conventional triphe n yl e n e - bas ed D LCs ( e. g . above -mentioned HAT and
SHU compounds) having molecules made of a c ore consisting of onl y one triphen y lene . Having
such a co re mad e of tw o sep arate t riph en ylen es, t he mol ecul es of t he KAL compounds might
presumabl y fo rm columns int erconnected to the neighboring columns in a wa y th at two
trip hen ylenes of a single mol ecule are the building blocks of two sep arate neighboring columns .

48

T h e y h av e a C r y phas e a t lo w tem peratu res . Wit h increasing temperature , they f irst from a C r y
phase, and then a Col h me s ophase , afte r that a n Is o p hase at hi gher t em per atur e s.

Figure 17 . (a) Chemi cal str uctures of the of the trip henylen e c r o wn ether - ba sed DL Cs; KAL465 and KAL468 . ( b )
H

exagonal lattic e formed in th e Co l h p has e . Figure was ta k e n fro m ref. 132F 133 .
3.3.1. Columnar Ionic Liquid Crystals
The sy nt hesis and the mesomorphic properties of the investigated linear - s hap ed
tetra meth y l ated g uanidinium trifla te ILCs, denoted as L C536 and L C537 , ar e given i n re f. 133F 134.
Th e ILC s LC536 and L C537 were s y nthesiz ed by Prof. Sabine Laschat’s group in t he Universit y
of Stuttg art . Their ch emi cal stru ctur es an d a schematic illustra tion of their molecula r or ga niz ation
are shown in Fi gur e 18. They consist of an aromatic guanidinium- based co re wit h a tr iflat e ( OTf)
counteranion a nd alk y l chains attached to the core via ether groups. At low temperatures, LC536
and LC537 form two d i fferent pla stic crysta lline phases (Cry 1 and Cr y 2 ). Upon further heating
from th e Cr y 1 and Cr y 2 phases, the y h ave a Col h mesophase. In the Col h phase fo r bot h m aterial s,
six m olec ul es built a hexagonal lattice in a la yer, and the layer s stuck on top of each other to form
columns. The triflate c ount eranions are located close to the guanidinium g roups in the aromatic
core. W it h furt h er h eat in g from the C ol h phase, they undergo a clearing tra nsition to t he Is o liquid
stat e. 1 34
(a)

(b)

49

Figure 18 . (a) Chemical structures o f the linear - sha ped tetram ethyl a ted gu anidin i um tr iflat e s ILC s; LC536 an d
LC53 7 . ( b) Si x mol ec ule s for mi ng the b uil di ng b lo ck s o f t h e he xa gona l latt ice i n t he hexa gonal c o l umna r p ha se . ( c)
Hexa gonal c o l

umnar phase. Figur e wa s ta ke n fr o m re f. 134F 135 w ith pe r mission (see Sect ion 4.3 for the pe rmi ssio n) .

3. 4. P repar ation of th e Sam ples f or the Inve stig ation of a CL C und er
Confinement
In this section, the confining host (anodic alumi num oxi de and si li ca memb ran es), the su rf ace
modification of the confining hosts as well as the related characte ri zat ion of the confining hos t,
and the pore filling procedure used in this work ar e presen t ed.
3.4.1 Confining Hos ts
Disk -shaped anodic alumi num oxide (AAO) mem bran es wit h a var iet y of pore diam eters ,
thi cknes ses an d poro si tie s w ere p urch ased fr om S mart Memb ran es Gm bH (Hal le, G erm an y) and
InRe dox ( Longmont, USA). In addition, s ilica m emb ranes h avin g a po re di ameter of c a. 12 n m
were pr epa red b y ele ct ro chemi cal an odic et chin g. The s il ica mem bran es w ere prod u ced b y Pro f.
Patrick Huber’s group in Hamburg University of Technolog y. The etching procedure used in this
work is give n i n ref. 25.
The po rosi ti es and p ore di amet ers of t he m embran es we re cha ract eri zed b y v olu met ric
N 2 -sorption m easu remen ts at 77 K. Volumetric N 2 - sor pt ion experiments were carried out b y an
autosorb iQ Quantachrome Instruments gas sorption s ystem. The determined pore sizes and
porosities (number of pore s per unit area) are given i n Table 1 tog ether with t he s pecifi catio ns o f
(a)

(b)

(c)

50

the producers . T he volumetric N 2 - sorption experiments were performed by Prof. Patrick Huber’s
group in Hamburg University of Technology.
Table 1. Pro p ert i es of the nanoporous mem branes
M embrane
Producer’s values

Determined values

Producer
Por e depth

( µ m)
Pore size, d

( n m)
Porosity

(%)
Pore size, d

( n m)
Porosi ty

(%)
Silicon

-

-

-

11.8 ± 0.2

61.2 ± 0.2

-

AAO

80

25

10

16.7 ± 0.6

16.0 ± 1.0

S ma r t Me mbranes

AAO

100

20

12

17.8 ± 1.8

19.4 ± 1.6

InR edox

AAO

80

30

30

24.3 ± 0.2

28.7 ± 1.0

Smart Mem br anes

AAO

80

40*

34

34.2 ± 0.7

44.0 ± 0.2

Smart Mem br anes

AAO

80

40* *

10

37.8 ± 0.7

15.8 ± 0.9

Smart Mem br anes

AAO

80

50

15

47.3 ± 0 .3

21.5 ± 0.2

Smart Mem br anes

AAO

80

80

35

72.9 ± 3.1

36.4 ± 1.6

Smart Mem br anes

AAO

100

120

12

95.0 ± 13.0

7.6 ± 0.6

InR edox

AAO

80

180

10

161.1 ± 9.7

13.8 ± 1.7

Smart Mem br anes

*is et c hed in oxalate acid. ** i s etched in sulfuric acid. Table was taken/adapted from ref. 25 with per mission .
The mem bran es hav e par all el c y lind rical hexa gonal ordere d po res which are open at both sides.
Fi gu r e 19 d emon str ates t hat the pore distribution of the membra nes is narrow, and the pores have
an alm ost parall el a rran gem ent .

Figure 19 . Scanning elect r on microscopy images (Zeiss Gemini Supra 40 ) of a n AAO m e m bra ne w i th a pore s ize of
161 nm . (a) The top vi e w of t he mem br ane. (b) T he side v ie w o f th e ed ge broken mem b rane. T he wh ite scale bars
represent

600 nm .
The measu r e ments w er e performed by S igrid Benem a nn from Bun d esanstalt für Materialf or schung
und

- prüfun g (BAM). Fi gure wa s take n fro m ref. 25 wi t h p er mission (see Chapter 5 for the pe rmi ssio n) .

(a)

(b)

51

(b)

(c)

3.4.2. Su rfa ce Mod if icatio n of th e C onf i nin g H os t s
The investigations for HAT 6 under confinement were carried out on both modified and
unmodified po re wall s. In t he l atter cas e , t he po re wal ls o f the A AO m emb ranes w ere chem ical l y
modifie d with n- octc y l phosphonic acid (C 8 H 19 O 3 P ; OP A) and n- octadec y lphosphoni c acid
(C 18 H 39 O 3 P; ODPA) following the pr o cedure reported in the literature. 135F
136 ,
136F
137 OPA has short er
leng ths of the alk y l ch ai ns comp ared to O DP A ( see Fi gure 20 .a and b ). OPA and ODPA w ere
purchas ed from Alf a Aes ar an d used as re ceived .

P
O OH
OH
P
O OH
OH
ODPA
OPA

Figure 20 . Ch e mical structu r e of the surf ace modifiers; ( a) n- octy lphosphon ic acid (O PA) an d (b)
n

- octadecylphosphonic acid (ODPA). (c) Schematic illustration of the surface
modi ficati on of AAO mem branes w ith
ODPA . T he ph oto on the r ight shows a w ater dropl et on a m odified m e mbra ne to v isuali ze th e hydroph obicity of t he
m odified m e m brane.

Figure was a dapted from ref. 25 w it h per mission ( see Chapter 5 for the per mission ).
A schem e o f th e s ur face t reatm ent pro cess is illustra ted for ODPA - modif ication in Fi gu r e 20.
Firs t, the h y drox ide groups on t he po re wal ls of t he A AO mem b ranes w er e activate d with 30%
aqueous H 2 O 2 solution f or 2 h at 45 °C, then dri ed at 120 °C for 15 minutes. The membranes ,
having the a ctivated h y dr ox ides on the pore walls, were immersed into a 4 mM solut ion of ODPA
(or OPA) i n a n - heptane/ isoprop y l alcohol soluti on (volume ratio of 5:1) for 48 h at 25 °C. The
memb ranes wer e th en washed s ev eral ti mes and s oni cat ed for 15 m inu tes wi th th e
n- heptane/isopropyl alcohol soluti on to remove any physically absorbed ODPA (or OP A ) . The
soni cated samp les w ere t hen was hed s eve ral t im es wit h t he n - heptane/isopropy l alcohol solution,
(a)

52

and then with acetone before bein g left to dr y ov ernight und er vacuum at room temperature. The
modifications of the pore walls were confirmed b y FTI R , given in Appendix I , in Fi gure S 5.
10 -2 10 -1 10 0 10 1
10 -1
10 0
10 1
10 2
10 3
10 4
10 5
10 6
10 7
10 8
10 9
Intensity [a.u.]
q [ nm -1 ]

Figure 21 . SA XS patt erns of unmodif ied (blac k soli d lin e) and O DPA - m odified ( red sol id lin e) em pty AAO
mem b ra nes h a ving th e p ore size of 38 n m. Dashed lin es rep resent s i mulations based on 2D core

- shell c
y linder m odel
for

unm odified (bl ack dash ed lin e) and modi fied (red das hed lin e)
mem b ra nes. The simulations were performed for a
core

- shel l c yli nde r, lo o ki ng o n -
axis, wi th the foll o win g para m eters : core diam eter 15 nm, polydis persity 0. 3 (in 45
po int s), she

ll th ickness : 2.2 nm, pol ydi spersity 0.25 (in 45 p oints ), cylin der angl e phi: 0 (a roun d -
axis ro tation), cylinder
angl e t heta: 0 (face

- on vie w ) , l e ngt h: 6 0 0 n m (o nl y af fect s th e int en sit y) - backg round: 1e -1
(av oiding deep dips). See
also

Appendix I . Figur e was ta k en fr o m re f. 25 wit h pe r miss i on ( see Chapter 5 for the permis sion ).
The long - r an ge ordering of both, the unmodified and modified membra n es, was studied by
Small Ang le X - ray Scatt er ing (SA XS) i n ord er t o es tim ate t he th ickn ess of th e ODP A - coati n g.
Fi gu r e 21 shows the measure d S AXS patterns and corresponding simulations. The simulations
were carried out b y mo del of 2D core - shell cylinder s from the SasModels libra r y. 137F
138 Simila r
mod els are app lied els ewh ere. 138F
139 ,
139F
140 The sc attering patte rn simulation s are done with th e
cy lindrical axis para llel to the be am , and using the sc attering le n gth densitie s estimated f or bulk
ODPA and alumina phases. Simulation s with diff erent she ll parameter s ( cy l inder dia m eter, sh ell
thickness, polydisper s it y) were c arried out. The simulation with a shell thickness para mete r of 2.2
nm is the clo sest approximation to the SAXS pattern of th e ODPA modified membranes. 14 0F
141 Hen ce,

53

it is concluded that the O DPA - coating has a thickness of ca. 2.2 ± 0.2 nm. The detail s of t he S AXS
measu rement s and som e add itional re sults are given in Appendix I , in Fi gu r e S 6.
3.4.3. Pore Filling Procedure
A reproduc ibl e pore filling procedure was deve l oped to embed HAT6 i nto nanoc hannel s 50 ,
and this procedure is followed to prepare the samples for the investigat ion of a CLC under
confinement. In short, the membranes were outgassed in vacuum of 10 -4 mbar at 473 K for 12
hours, to clean the por es and remove a dsorbed water. Then the membrane s were tra ns ferred under
vacuum to an argon - filled glove box . The amount of ma te rial requir ed to fill the me mbranes
completely was calculated from the porosit y and t he volume of the membranes according to
m

HAT6
= �Φ

AAO
x �π � d

AAO
2 � 2 λ

AAO
�� x ρ

HAT6 (31)
where Φ AAO is the porosity, d AAO is the diame ter of the me mbran e, λ AAO is the thickness of the
memb rane and ρ HA T6 is the bulk density of H AT6 found to be 0.92 g cm -3 . 141F
142 A bulk- like density
was ass umed w h en HAT 6 is confined into nanopo res. The calculate d amount of the liquid c r ysta l
and a small surplus of the cal culat ed amount w er e pl ace d on the top of the m embrane a nd he ated
to 418 K in the iso tropic state. At this tempera ture, the pore s were f illed by melt infiltr ation under
argon atmosphere for 48 h. Afte r filling , th e excess of the material o n the top and bottom of th e
memb ranes w as carefu ll y scratch ed off w ith a sh ar p scal pel .
The f illing degree of the membra nes with HAT6 was estima ted by TGA. A complete pore
filling was obtain ed for all samp les investig ated in this study (see Appendix I , Fi gure S 4).

54

CHAPTER 4 – C OLUMNA R LI QUID CR YSTALS IN THE B ULK
STATE
4.1. Triphenylene - B ased D iscot ic Liqu id Cryst als
This sectio n is reproduc e d /ad apted fr om A. Yildirim, A. Bühlmey e r, S. Ha yashi, J. C. Haenle,
K. Sentker, C. Krause, P. Huber, S. Lasc h at, A. Schönhals, Multiple glass y d y namics in di pole
functionalized tripheny l ene - bas ed di sco tic l iq uid cr y s tal s rev ealed b y bro adban d di electri c
spect rosco p y and ad vanced calo rim etr y – Assessment o f the mole cular or igin ,
Phys. Chem . Ch em. Ph ys . 2019, 21, 18265 –18277 with permission from the PCCP Owner
Soci eti es ( D O I: https: //doi.org/10.1039/C9CP03499D).
With respe ct to the understanding of molecular d ynamics of triphen yle ne - derived columnar
DLCs, a comparison of s y m metrical hexakis(n - alk y lox y) triphenyle n es HATn with struc turally
related dipole functionalized low s y m metr y triph e nylenes seems highl y r ecommended. HATn are
model DLCs and considered as “wo rking horse” of the D LC research, which have been ex tensively
studied. 4 For this purpose, a series of pentapent yloxy triphe n y len es car r ying di ffe rent fun ct ion al
units, SHU0 9 - SHU12 (see Fi gur e 16) , was chose n because t he y provid e dipole functionalities and
also H -bonding abilit y fo r SHU12 .
The monofunctionalized compounds wer e investiga ted in a sy stematic way to reveal the
influence of t he dipole f unctionalization on the mesomorphic prope rties, the phase behavior and
the m olecu lar d ynami cs. Th e lat t er point is of p articular importance to understand the c harge
transport in such s y ste ms which is the ke y p ropert y f or their applications such as organic
field - ef fect trans is tors , s ol ar cell s or as nano wi re s in mol ecul ar elec tronic s and to tune D LC s for
applications. The mesomorphic pr operties were s tudied by P OM , XR D , and DSC , wh ich were

55

compared to the unfunctionalized s y mm etrical t riphenylene- based DL C H AT5 (s ee Fi gure 15b).
The molecular d y n amics of all compounds were investi gate d b y a combination of BDS , FS C and
SHS. To best of our kno wledge , it is the first study appl y in g F SC to discotic liquid cry stals. SHS
investigations were conducted at low tempe r atures using helium as purge gas. This unique
combination of methods to investigate the m olecular d y namics has never been reported before and
en ables to address both the intercolumnar space and the columns as well.
Be sides localized fluc tu ations, sur prisingly mu lt iple gla ss y d y namics were detec ted for all
materials for the first time. Glass y d y namics were proven for both processes unambiguously due
to the e x traordinar y broad frequenc y r ange covered. The α 1 - process is attributed to the c ooperative
fluctu ations of the alky l ch ains in t he in te rcolu m nar s pa ce b ecau se a p ol yeth ylene - like gla ss y
dyna m ics is obs erved. This corresponds to a glass transition in a confined three - dimensional space.
The α 2 - proc ess found at t emper atures l ower th an α 1 - process, is assig n ed to the cooperative
fluctu ation of tra nslational in- plane movements and/o r small ang le rotational flu ctuations of the
triphenyle n e core inside t he part of distorted columns, where the frustration of the column packi ng
is present. This result ca n be considered a s a glass transition of a 1D fluid. There for e, obtained
results are of general importance to understand the glass transition, which is a topical unsolved
problem of condens ed matt er sci en ce .
4.1.1. Meso morph ic Prop erties
The liqu id crysta lline textures of the monofunctionalized tripheny len e derivatives
SHU09 - SHU12 wer e inves ti gated b y PO M. Tw o tex t ures o f SHU1 2 are depi cted as ex amp les i n
Fi gu r e 22 taken during cooling fr om t he isotropic phase. The P OM pictures for the other
compounds are shown in Appe ndix II , i n Fi gu r e S 7-S10 . The taken pictures showed dendrimer i c
growth and pseudo focal conic fan-shaped te x tures , which are typical for Col h mesoph ases.

56

Figure 22 .

POM picture of SHU1 2 at 373 K f or the Is o pha se (left) and at 34 6 K for t he Col

h
m e so pha se (r ig ht) take n
dur in g co o ling fr o m the

isotro p ic liquid ( coo ling rate 5 K mi n -1 , m a gnif ication 200x).
To est im ate th e l att ice param ete rs o f t he colu mnar s tru ctur e, X RD meas urem ent s we r e
perform ed wh ere the res ul ts are sum ma riz ed i n Tab le 2 . The X - ra y patter n for all triphe n y lene
deriv ativ es SHU09 -SHU12 dis play a diffuse halo in the q vector ran ge around 1.4 Å -1 which is
due to the fle x ible alky l chains. F urthermore, the d iffra ction pattern o f SH U11 shows f our dist inct
reflections in a ratio of the moduli of q vectors of 1 : 1/ √ 3 : 1/2 : 1/ √ 7 which a re index ed to (10),
(11), (20), a nd (21 ). These data are characteristic for a C ol h me so phase wi th a p6mm sy mmetr y
( Fi gu re 23 ).
The diffraction pattern of the compound SH U10 shows also the (10), (20) and the (21)
refle cti ons wher e that of SHU09 and S HU12 have only the peak corresponding to (10) ( For details
see Appendi x II , F i gu r e S 11-S17 ). Due to the structur al similarity of the molecules , t he ex is tence
of a Col h phase can be assumed for these compounds, despite the absence of hi gher order
refle cti ons . The l att ice pa ram eters r an ge from 19.9 Å to 20.4 Å . The l att ice par amet er of SHU 10
determined here is simila r to that found for SHU1 0 in the literatur e (a = 20.3 Å at T = 303 K). 70
The further discussion is organized in the foll owing way. The results obtain ed for SHU0 9 (ph ase
behavior) a nd S HU10 ( m olecu lar mo bil it y) are di scus sed i n det ail as sho wcases foll ow ed b y an
100 μ m

100 μ m

57

int ense compa rison of th e behavior of all material s including HAT5 wher e th e ori gin al dat a are
coll ected i n Appendix II .
Table 2 . Res ults of the X RD exp eri ments for monofunctio na lized tr iphenylene d eriva tives SH U09 - SHU1 2
Co mpound M esopha se Lattice spacing /
Å

d- spacing / Å
experimental (calculated)

M iller Indices
S HU09
Col

h
at 363 K
p6mm

a = 20.20
17.5
4.5

(10)
halo

SHU1 0 Co l h at 353 K
p6mm a = 20.40
17.7

6.6 (6. 7)
4.5

(10)

(21)
halo

SHU1 0
fro m r e f. 70

Col

h
at 303 K
p6mm

a = 20.30
17.6
3.5

(10)
π - π

SHU1 1 Co l h at 353 K
p6mm a = 20.00
17.4

10.0 (10. 0)
8.9 (8. 7)
6.5 (6. 6)
4.5

(10)

(11)
(20)
(21)
halo

SHU1 2
Col

h
at 353 K
p6mm

a = 19.90
17.3
4.4

(10)
halo

HAT5
fro m r e f. 70

Col

h
at 353 K
p6mm

a = 19.86
17.2
3.6

(10)
π - π

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
(21)
(20)
(11)
Intensity [a.u.]
q [Å -1 ]
(10)

Figure 23 . WA XS diff ractogram of SHU11 at 353 K for t he Col

h
meso p hase with t he correspon ding diffract ion
patter n (inset).

Fi gu r e 24 depict s th e X - ra y pattern fo r HAT5 m easured w i th the setup discussed in r ef. 21 at
room temperat ur e as r ef erenc e fo r a C r y ph ase. The diffractogram show s numerous reflections

58

corre s ponding to the C r y phase. This indicates a more or less cr ystalline structure . Mor eover, in
the q range from ca. 1 Å - 1 to 2 Å -1 an amorphous halo is present which can be tak en like for the
hexagonal c ol umnar liquid cr y stalli ne as an indication for nanopha s e separated structure
containing some disorder. It was discussed in r ef. 21 that this part of the X - ray patte rn is quite
similar to that of semi - cryst alli ne po l y eth y len e. T herefo re, i t is concl ud ed th at al so t he C r y s tat e
consists of columns and disordere d alk y l chains in between. For the SHU materials (besi des
SHU10 ) also a C r y phase is assumed at low tempe ratures which might be less ordered than that of
HAT5 as refe renc e.
0.4 0.8 1.2 1.6 2.0 2.4
Intensity [a.u.]
q [Å -1 ]
Amorphous Halo

Figure 24 . XRD diff ractog ra m of H A T5 at 303 K for t he Cry p hase.

4.1.2. Phas e Behavi o r
The phase behavior of the SH U compounds and HAT 5 was ch ara c teri zed furth er b y
conventional DSC experiments. F igu re 25 a sho ws DS C t herm o grams o f SH U09 for the firs t
cooling and the second h eating run. A comparison of the DSC t hermograms of S HU09 - SH U12
and HAT5 for the sec ond heating runs are give n in F igu r e 25b. The e s timated phase transition
temp eratur es and ent hal p ies o f the m ateri als are col lect ed in Table 3. T he DSC investigations

59

reveal ed t hat al l D LCs, ex cept SH U10 , fo rm a Cr y phas e at low temperatur es. At higher
temp eratur es , a Co l h ph as e is es tab lis hed, wh ere a hex agon al lat tice i s b uil t b y s ix self - assembl ed
columns. With further increase of temperature from the Col h phase, all materi als und ergo a cle ari n g
trans ition to the I so phase . Additiona ll y , a cr y stalli ne to crys talline tr ansition is de te cted d u ring the
heating run at 333 K, 2 88 K and 340 K for S HU09 , SHU11 and SHU1 2 , resp ect iv el y (see
Appendix II ). Fro m the literatu re , it is known that SHU1 0 cry st alizes only from solutio n. 70 This is
also confirmed by X- ra y m easurem ents (s ee Fi gu r e S 13).

Figure 25 . (a) D S C t h e r mo g r a ms o f SHU0 9 for the first cooling a nd the second h eat ing run at a r ate of 10 K mi n -1 .
Das hed li nes po int ou t t he p ha se tr ansi ti on t e mp er atur es ob se r ved d uri ng t he se co nd hea ti ng runs. Do tt ed li ne ind ica te s
the gl a ss tr an si tio n tempe ra tur e o bs er ved dur ing t he se co nd h

eat in g run. (b) D SC the r mo gra ms o f SHU 09 - SHU1 2
and
HAT5

for the s eco nd heating run at a h ea ting rate of 10 K min -1 as indicated.
Table 3 show s th at t he tem peratu re r an ge of the C ol h mesophase i s consider abl y b roadened for
all monofunctionalized tripheny lene derivative s , ex cept for SHU12 , compar ed to unfunctionaliz ed
symme trical HAT5 . This result ca n be better comprehende d f rom the bar cha rt repre s entation of
the me sophase stabilities, which is given in Fi gure 26 . For triphenyle n es function alized with este r
groups suc h as S HU09 and SH U10 , a stabilizatio n of the columnar stru cture an d a wid er ran ge of
2D lattic e correla tions with the functio nalization wer e repor ted. 70 ,
142F
143

(b)

(a)

60

Table 3. P hase trans it ions temperatures and en t halpies determined by DSC
Co mpound

T g,2 thermal [K]
T

g,1
thermal [K]
(∆c

p
[J K

-1
g

-1
])

Pha se
T [K ]
(∆H [J g

-1
])

Pha se
T [K ]
(∆H [J g

-1
])

Pha se
SHU0 9

142.7

217.1 (0. 29)

Cr y

337.1 (2 4.0)

Col

h

411.7 (1 3.4)

Iso

SHU1 0

140.5

213.5 (0. 32)

-

-

Col

h

452.3 (2 1.9)

Iso

SHU1 0

fro m r e f. 70

- 215 (-) Cr y 317* ( -) Col h 450 (16.8) Iso
SHU1 1

145.8

231.8 (0. 05)

Cr y

309.7 (0. 3)

Col

h

450.8 (1 4.7)

Iso

SHU1 2

142.9

258.5 (0. 15)

Cr y

345.2 (3 6.0)

Col

h

371.6 (5. 9)

Iso

HAT5
162.3

206.6 (0. 15)

Cr y

341.6 (4 8.0)
Col

h

395.6 (1 3.5)
Iso

HAT5

fro m r e f. 21

- - Cr y 341.7 (4 2.3) Col h 396.1 (1 2.1) Iso
* T he p hase tr ansitio n temper atur e is taken fro m ref.

70 . As it is r epo rted in r ef. 70 , SH U10 cr ystallizes o nly fro m
solutio n.

This is re lated to the specific conformation of the ester groups including also dipole-dipole
intera ction. Similarly , th e dipole - di pole interactions of trifluorom ethyl groups ma y l ead to the
broader t emper at ure r an ge of C ol h mesophase, observed for SHU11 . In contrast, the temper at ure
ran ge of t he Col h mesophase of SHU1 2 is quite n arrow. The reason of th e narrow Col h phase for
200
300
400
500
SHU11 SHU12
SHU10 SHU09
HAT5
Iso
Iso
Col h
Col h
Col h
Iso
Cry
Cry Cry
T [K]
Cry
Col h
Col h
Iso Iso

Figure 26 . Mesop hase s tabilit ies of SHU09 - SH U12 in c omp ar iso n with t ha t o f HAT5 , co nstructed fro m th e res ults
give n i n

Tabl e 3 .

61

SHU12 might be the differe nt interactions between the polar groups which might influence the
structure and the stabilit y of the columns. In the molecular s t ru cture of SH U1 2 , th ere ar e et h er an d
hydroxyl gr oups which p resumabl y form h ydrogen bonds.
In th e Cr y phas e, a step - li ke ch an ge is obs erv ed in the t emp erat ure d epen den ce of t he heat fl ow
for SHU09 , whi ch is charact erist ic fo r a therm al glass trans it ion . Al l DLCs d is cuss ed here al so
undergo a ther m al glass transition. The thermal glass transition temperatures (T g,1 t h erma l ) as w ell as
the corresp ondi n g in crem ents in th e sp eci fic heat capacit y (Δc p ) are summarized in Table 3 . I n the
same t emper atur e ran ge o f T g,1 th erm al found for SHU09 -SHU12 here, a glass transition is observed
also for sev eral ot her D LC s. 25 , 40 , 70 , 135 ,
143F
144 As it is reporte d for those D L Cs, a cer tain disorder cause d
by nanophase separation of the aromatic cores and the alk yl chains surrounding the aromatic core,
is held responsible for t he glass transition. The halos obser ved in the XRD diffrac to grams of
SHU09 - SHU12 further support the nanophase sep aration.
4.1.3. Mo le cul a r Mobility
The molecular d y n amics of the dipole functionaliz ed tripheny l ene derivates S HU09 - S H U 12
and that of HAT5 were i nv esti gated b y BDS. An ex ampl e for t he BDS i nves ti gation s is depi cted
in Fi gu r e 27, in a 3D repr esentation of the dielectric loss spectra as a f unc tion of frequency a nd
temp eratur e fo r SHU10 . Besides a conductivity contribution at low frequencies and high
temp eratur es , th ree diel ec t rical l y acti ve proc ess es den oted as γ -, α 2 - and α 1 - relax at ion are obs erved
as peaks in the di electr i c los s for SHU10 . A simi lar behavior is observed for the compounds
SHU09 , S HU11 and SH U12 . For HAT5 , two diel ectri call y act ive pr ocess es, the γ - and t h e
α 2 - re l axation, are observed. For SH U09 and SH U12 , al l rel ax at ion proces s es tak e p lac e in the Cr y
phase. For SHU11 , the α 1 - process is also observed partly in the Col h ph ase du e to t he relat ivel y
low value of the pha se transition temperature from the Cr y to the Col h phase. F or S HU10 , the

62

relax ati on p rocess es tak e p lac e in t he Co l h ph ase be caus e S HU10 does not undergo the phase
transition from the Col h to the Cry ph ase during cooling.

Figure 27 . 3D represen tation o f th e dielectric loss as function of frequency and temperature for SHU1 0 fo r t he sec o nd
heat i ng r un.

Arrows indicate th e dielectric processes. T he d ata i s s ho wn fo r the C ol h mesophas e o f SHU1 0 .
The rela x ation processes were quantitatively a nalyzed b y fitting the model function of
HN -function , given in eqn. (13) , to t he dat a. Examples o f fits of the H N - function to t he processe s
of S HU10 are given in F igu re 28 . For ea ch t em perat ur e, t he relax at ion rates 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 are obt ain ed
from t he fi ts. Th e obt ai ned relax ati on r at es 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 for al l det ect ed pro ces sed are pl ot ted v ers us
inv erse tem pe ratu re fo r S HU10 in t he r elax at ion map (s ee Fi gu re 29 ) including the data for HAT5
for comparison a s an ex am pl e for th e tem pe ratur e depen den cies of th e r elax ati on p rocess es o f t he
monofunctionalized triphenylenes. In addition, the relaxation maps fo r the other SHU compounds
as well as t he dat a fo r the rel ated r el ax atio n pro cess es, are sho w n in Appendix II in Fi gu re S 23-S24.
Cond uct ivit y

α 1

α 2

γ

63

-2 -1 01234567
-2.4
-2.0
-1.6
-1.2
-0.8
log ε ''
log (f [Hz])
133 K
163 K
153 K
233 K
243 K 263 K
α 2
γ
α 1

Figure 28 . Frequency dependency of dielectric loss for SHU1 0 for the second heating at the indicated temperatures.
Arrows point ou t t he dielectrically active relax atio n processes.

Solid lines ar e the fit s of the HN - functio n to the da ta .

The tem per ature dep end ence o f the relax at ion rat es of th e γ - r elax at ion was approximated b y
the Arrhe ni us -equation (eqn. (1) ). Th e tem per ature d epend en ces of th e rel ax ati on rat es of t he
γ - proc esses of S HU09 - S HU12 an d HAT5 are q uite similar to that of p ol y eth yle n e ( PE ) (se e
Fi gu r e 29 ). 40 Thus, γ - proce ss of these materials is a ssigned to the localiz ed fluctua tions taking
place in the a l k yl c h ains probed even further b y t he polar groups. The activation energies for the
γ - relax at ions ar e calculated to be 19 kJ mol -1 fo r S H U09 , 17 kJ mol -1 for S HU10 , 12 kJ mol -1 for
SHU11 , and 26 k J mol -1 for SH U12 and HAT 5 (see Appendix II , Tab le S 1 ). While the activatio n
ener gies fo r SH U09 -11 are r ather l ik e, th at for S HU12 i s es sent ial ly higher. To understand this
result, one must consider that among the triphen ylene der i vatives, the substituents of SHU12 are
the only ones which can form hydrogen bonds with each other. The h y d rogen bonds will i ncrea s e
the constrains to the localized molec ular fl uctu ati o ns and ther efo re it s acti v ati on ener g y.

64

2 3 4 5 6 7 8
-4
-2
0
2
4
6
8
10
BDS
FSC DSC
α 2
log(f max [Hz])
1000 / T [K -1 ]
γ
SHS
α 1

Figure 29 . C o mbin ed relaxation m ap o f S HU10 constru cted from data obtain ed b y BDS, FSC and DSC . Red sy mbol s
–

da ta fo r SHU10 a nd bl ue s ymbo l s – data for HAT5 . T r ia ngles – α 1 - r elaxation (BDS); open circles – α 2 -
relaxatio n
(BDS) ; filled square s

– γ - rela xation (BDS) ; op en stars – α 1 - re laxation (FS C); o pen pen tagons – α 2 -
relaxat ion (SHS) ;
and filled stars

– thermal glass transition temperatures (DSC). T he relaxation r ates were ca lculat ed b y eqn . ( 3) fo r
t he
give n F SC a nd D SC d ata .

Different symbols are us ed to differentiate between the diff er ent relaxation processes.
Solid
lines are t he fits o f VFT

- equation ( eq n. (2)) to the correspondin g data. Dashed lines are fits of the Arrhenius -
eq uatio n
(e qn.

(1) ) to the data. Black filled tria ngles denote the die lectr ic α - relaxatio n of PE tak e n fr o m r ef. 14 4F 145
. B l a c k
hexagons s ymbolize the die lec tric

γ - relaxatio n of PE ta ke n fro m r e f. 40 . Black crosses r epr esent the calorimetric PE
-
like gla ss y d yna mic s o f p o l y(n

- de c yl methacrylate) f ro m ref. 145F 146 . B lack open hex ago ns sym bo lize the dielectric PE
-
like gl as s y d yna mi cs o f pol y( n

- decyl methacryl ate) taken from ref. 1 46F 147 . The dat a shown he re corres pond to th e Col
h
me sophase of

SHU1 0 and for the Cry p hase of HA T5 .
The rel ax ati on rates o f t he γ - pro cess es v ar y sl ig htl y, which ar e ran ged f ro m fast to slo w:
SHU10 > SHU09 > S HU1 1 > HAT 5 > SHU12 . A simil ar ordering is fou nd for the rankin g of the
latt ice s pacin g (or t he di stan ces bet we en th e colu mns ) in t he C ol h phase, shown in Table 2. T h e
latt ice s pacin gs were p lot ted against the rel ax at ion rates of γ - pro cess at the ch osen temp eratu re ,
shown in Appendix II in Figu re S 25, and the plot shows a line ar relation. S ince the same rankin g
of th e dis tan ce betw een t he col umn s i n th e C r y p hase i s reali z ed, 21 the ranking of the relaxation
rates c an b e ex p lain ed b y a self - confineme nt effect orig inating fr om th e confine ment of the alky l
chain in between the column. I n other words, a shorter the di stance between the columns causes
higher restrictions on the l ocalized fluctuations in the groups of the alkyl c h ains.

65

The tem perat u re dep end en cies o f the rel ax atio n rates of the α 1 - and α 2 - relaxations are curved
in the relaxation map, indicating gla ss y d y namics . Hen ce, t h e y w ere appro x imat ed b y the
VFT - equation (eqn. (2) ). Furtherm o re, as a com pl e ment ar y techniq ue to BD S , FSC was p erfo rmed
to fu rther i nves ti gate t he glass y d y nam ics d et ected b y BDS. In BDS, mol ecu lar d ynam ics i s p robed
through the dipole f luctu ations. Unlike BDS, FSC probes the g l ass y t ransition through the e ntrop y
fluct uat i ons. FSC thermograms, obtained b y performing measurements with heating rates from
10 K s -1 to 10000 K s -1 , a re shown for SHU10 in Figu re 30 and for SHU0 9 , SH U11 , SHU12 and
HAT5 in Appendix II in F i gu re S 27-S29.

180 200 220 240 260 280 300
Heat Flow [a.u. ]
T [K]
2000 K s -1
1000 K s -1
500 K s -1
200 K s -1
100 K s -1
50 K s -1
20 K s -1
10 K s -1
Endo

Figure 30 . FSC t her mo gr a ms o f SHU10 for heating runs at different heating rates as indicated. Dashed lines indicate
the est i mated thermal glass transition tem per atures. The thermograms are shifted along t he y

- scale f o r clarity.
The st eps i n t h e he at flo w s in dicat e a glas s t ra nsition, which is shifted to the highe r tempera ture
wit h in creasin g heat ing r ate as ex p ected. The t emperat ur e of t he hal f st ep - height of the ste p was
taken to d etermi ne t he gl ass t ransi ti on t emperat ure fo r each heati n g rate. The h eatin g rat es are
convert ed u s in g eq n. (3) into thermal r elaxation rates to compare the relax ation ra tes estimate d
from B DS measureme nt s with the the rmal ones. The esti mat ed r elax at ion rate s to ge ther with
corre s ponding glass transition temperatures ar e in cl uded i n Fi gure 29 together w ith th e dielectr ic

66

data. Additionall y , the data measured by conventional DSC were also conver t ed into a relaxation
rate and added to Fi gu r e 29.
The rel ax atio n rates es ti mat ed b y FSC and con vent ion al DS C ag ree wit h di elect ric
α 1 - proc esses. This agreement was obs erved for al l monofunctionalized triphenylene derivatives.
This result proves that b oth BD S and FSC probe the same molecular proc ess. The both data sets
also agree wi th t he relax at io n rates esti mat ed fro m conven ti onal DSC measurem ents for T g, 1 t h erm al
wit h a heat in g rate o f 10 K min -1 . I t is further imp ortant to no te that the F S C data of HAT5 ag ree
with the calorimetr ic and dielec tric data of S HU10 but not with the dielec tric rela x ation ra tes of
HAT5 .
Haverk ate et al. 49 revea l ed the structure and dynamics of HAT6 at p icos econd ti mescal e b y
compa rin g the results of mo lecular dy namics (MD) simula tions by ad d res sin g mainl y th e co res. It
should be noted that the model used for simulations consist onl y of twelve columns having six
molecules. It does not consider the full liquid crystalline structure. The y fo und two ch aract eris ti c
modes of molecular motion; fast and slow m otions w hi ch are separated by two order s of
magnitude . Th e slow proce ss is attribute d to rotationa l movements of th e core (tilt an d twist),
where th e flu ctuat ion s of t he core an d alk yl ch ains are cor relat ed (s ee Fi gur e 31 a) . The fas t pr ocess ,
which is found approximal two orders of magnitude faster than the slow process, is attributed to
the translational movements of the c ore (parallel and perpendicular to the column axis), where
alky l chains motion s only weakly corre late with the p arallel motion of the c ore (see Fi gur e 31b).
At lea st the simula tions evide nce that th e columnar like structur e allow s for s ome m ol ecular
mobilit y inside the column which can be also s mall angle rotational fluc tuations. These findings
about fast and slow motions of H AT6 b y simulations could shed light on the molecula r assignment
of the fast (α 2 - processes) and slow (α 1 - proces s es) glass y d y n ami cs det e cte d for t he t riph en y l ene

67

deriv atives. I n the following it is firstly concentra ted on the α 1 - pro ces ses. The t emper atu re
depend en ce of t he relax ati on rates of th e α 1 - processes for SH U10 have cl o se res emb lance wi th
that of dielectric α - process of PE 145 (see Fi gu re 29 ). A similar behavior is observed for all S HU
materi als (s ee Appendix II , Fi gur e S 23 ). PE - l ike gl ass y d ynamics h ave been repor ted for col um nar
D LC s 33 , 40 , and columnar I LC s 1 35 . Moreover, poly m ers havin g longer n - alk y side chains, which
form a nanopha se sep arated morphology 22 , 1 47 , show a PE - like glass y d y na mics due to nanophase
separat ed alk yl chains . This means that th e obser ved similarity of the rel a x atio n rat es of the α 1 -
rela x ation is not accidental but is typical for nanophase s ystem having longer alk yl c h ains. This is
demonstrated for poly(n - d e c yl m ethac r y l at e) inv e st igated b y BDS. The d e tect ed PE - like g lass y
d y n amics ass i gned to PE - like cooperative fluctuations of the alky l s ide chains, which a re
connecte d to the main chain via ester linkage 147 , o verlaps with th e dielectric da ta measured for
SHU10 . This result gives further evidence that α 1 - relaxation of the SHU mat erial s h as t o b e
assigne d m ainl y to the c o operative fluctuations of the alky l chains in the intercolumnar space . Thi s
corre s ponds to a glass transition in a confined 3D space. A further proof of this assignment comes
from th e calor imetric r elax at ion rates o f t he PE - like glass y d y nam i cs m easu red al so fo r
poly(n- d e c yl metha cr ylat e) 146 . Thes e dat a are incl uded in F igu re 29 an d a gree wi th t he di elect ri c
and t hermal relax ation rate es timated for th e α 1 - rel ax ati on of SHU10 and are also close to those of
the other SHU ma terials. This assig nment agrees w ith the observ ation that the tempe rature
depend en ce o f the r el ax atio n rat es of t h e α 1 is more or less simila r for diff erent triphenylenes , as
shown in Figu re S 23 . The assignment of the α 1 - rel axation to fluctuations of the alk y l chains in t he
intercolumnar space does not exclude small angle rotational fluctuations of the cores. As it is
evidence d b y M D simulations, 49 t he rotational fluctuations of the c ores are coupled to this process.
The assignment of the α 1 - re laxation is illustrate d in Fi gu r e 31 a an d c. The a lk yl chains are lo cat ed

68

in the intercolumnar a re a between the columns built by the triphen ylene unit e s. This corresponds
to a s elf - ass embl ed or a sel f - or ganiz ed sp ati al co nfi nemen t as al so dis cuss ed for t he ex cess low
frequen c y ex citat io n (Bo son Peak) i n th e rel at ed m ateri al s. 21 T herefor e, t he α 1 - re lax ation is
consi dered as a glas s tran s ition in a 3D confine m ent.

Figure 31 . Illustratio ns of the character istic (a) tilt and t wist m o tions (slo w process) and ( b) par allel and p erpendicular
m o tions (fast process) for a si ngle molecule, adapted from ref .

49
. Illustratio ns of coop erative molecular fl uctuation s
are attr ibuted to (c)

α 1 - proc ess and (d) α 2 - pr oc esse s fo r SHU10 . Blue colored pa rts of S HU10
m olec ules indicate the
parts are assig ned to the glassy d ynamics an d red colored parts of t he molecules ar e the parts w here these glass
dynamics ar e sensed by BDS.

Fi gu r e 29 sh ows t hat t he diel ectri c and th er mal r el ax atio n rat es of α 1 - relax a ti on for S HU10 are
similar to the thermal re l axation rate s of α 1 - relaxat ion for HAT 5 , although the f ormer material is
in the he x agonal ordered liquid crystalline state a nd the latter in the Cry phase. This indicates that
(a)

(b)

(c)

(d)

69

the molecular or i gin of the α 1 - relax at ion is s imilar as ex p ected b ecause it is ass igned t o th e
fluctuation of the nanop hase sep arat ed alk yl tail s . M oreover , it fu rther ev iden ces that the phase
structure of the C r y and the Col h phase is not that different on a molecular level. Also, the da ta for
SHU09 agree with the results obtained for HAT 5 and SUH 10 . Th e d at a f or th e α 1 - rel ax atio n of
SHU11 and SH U12 are slightly shifted t o hi gher tem perat ur es bec aus e dif feren t in ter acti ons li ke
h y d ro gen b ondi n g take p l ace betw een t he alk yl ch ai ns.
As discussed above, the FSC data of HAT5 agr ee wit h calor imet ri c and d ielect ric d at a of
SHU10 but not with the d ielectric relaxation ra tes of HAT5 . Therefore , the question arises whether
the d ielect ric pro ces s m eas ured for H AT 5 corresponds t o the α 1 - or m ay be to the α 2 -pr ocess.
Similar de viatio ns in t he temperat ur e depen den cies of t he relax at ion rates of t he di elect ric
relax ati on p rocess hav e b een r epo rted, wh en t he un fun cti onal iz ed s ymmetri cal HAT 6 is comp ared
with asy mmetric al a monofunctiona lized HAT6 ( H AT6 -C 10 Br ). 40 A corresponding beh avior is
observed for the triphen ylene - ba s ed symme trical DL C THA11 co mpar ed with the as y m metri cal
monofunctionalized DLC Tri 11 144 . T ri11 has a quite similar c hemical st ructure to SH U09 and
SHU10 and can be al so c on sid ered as monofunctionalized H AT5 . T herefo re, t he g l as s y dynam ics
of Tri11 and THA11 co mp ared wit h th at of SH U09 - SH U12 in a rel axation map given in F i gu re
S24. Fi gu re S 24 depi cts that th e temp eratur e depen den ce of rel axat io n rates of Tri11 overlaps w ith
that of SHU09 - S HU10 , however , t hat of symmetrical THA11 devi ates like HAT 5 and HAT6 .
This comparison might fur t her evidence that th e d iel ectric p rocess me asu red for H AT5 is not
α 1 - proc ess observ ed for the functionalized discotic liquid cry st als but might be due to the
α 2 - process.
To proof whether the α 2 - process corresponds to a second of glass y dyna mi cs in these s y stems,
calorimetric inve s tigation should be useful. Unfortunately , b y conventional DSC experiments

70

using nitrogen as pur ge gas cannot be carried out at the required low t emperatures below 173 K.
Thus , DS C m easur emen t s wer e also conducted at temperatures down to 103 K usin g helium as
purge g as. S elect ed ex amp les for th ermog rams for the D LCs for t hese m eas urem ents are given i n
Appendix II in Fi gu re S 22 . A g lass transition a t lower tempera tures than T g,1 therm al , whi ch is called
T g,2 th erma l , is detected for the all monofunctionalized tripheny l ene derivat ives. To best of our
knowledge for the first ti me, a glass transition for D LCs at such low t emperatures is observed
besides the one observed commonl y at te mp erat ures ab ov e 17 3 K. Th e est im ated v al ues fo r
T g,2 th erma l are given i n T abl e 3. Δc p at this low te mperature gla ss transition is too small to be
quantitatively discussed. Furthe rmor e, the α 2 - process es of HAT 5 and SHU10 were al so
investigated by conducting SHS ex p erimen ts , employ in g te mperature mo dulated DSC in the step
scan app roa ch 128 , at low tempe ratures using helium as purge gas. Fi gu r e 32 g iv es the tempe r ature
dependenc e of the real p art of t he com plex s pecif i c heat cap aci t y , 𝑐𝑐 𝑝𝑝 ′ , at a frequency of 3.3 x 10 -2
Hz for H AT5 and SHU 10 . Th e t emp eratu re d ep end enc y of 𝑐𝑐 𝑝𝑝 ′ shows a s te p - like increa se with
incre asing tempera ture which is char a cter istic for a glass tran sition.

140 150 160 170 180 190
0.6
0.7
0.8
0.9
120 130 140 150 160 170
0.5
0.6
0.7
0.8
c
p
' [J/gK]
T [K]
T dynamic
g,2
c
p
' [J/gK]
T [K]
T dynamic
g,2

Figure 32 . Temperature dependence of the real part of the c omplex specific heat capacity , 𝑐𝑐 𝑃𝑃 ′ , for (a) HAT5 and (b)
SHU1 0

at a m odulation freque ncy of 3.3 x 10 -2 Hz. Solid lines indicate t he mid - s tep p ositions.
(a)

(b)

71

SHS dat a were an al y zed b y takin g th e m id - step position of 𝑐𝑐 𝑝𝑝 ′ (T) to determine a corresponding
T g dy namic f or the give n frequenc y. A th ermal re la xa tion r ate is also estimated for T g,2 th erma l obtained
from DSC investigation using eqn. (3) . The s e calorime tric data agree w ell with the dielectric
relax ati on rat es fo r t he α 2 - relax at ion as d epict ed in Figu r e 29 and Figu r e S 23 -S24. T his agreem ent
proofs fi rstl y that the dielectric α 2 - relaxation corresponds to a low tempe rature glass transition for
the SHU materials. Secondly , also for HAT5 the di electr ic dat a co inci den ce wi th t he rel ax atio n
rate s obtained from c alorimetric inv estigations at lo w tempera tures. This result p roves that the
diel ectri c p rocess o bserv ed for HAT5 corresponds to the α 2 - rel ax ati on. A di elect ric α 2 - relax ati on
is not observed for HAT5 due to the lack of a net dipol e moment.
The α 1 - relaxation is assigned to cooperative fluctu ations of the alk yl chain in the inter columnar
spac e correla ted to rotational fluc tuations of the core (tilt and twist) . Thi s molec ular process is
frozen at temperatures below T g,1 t h erma l . Freezing of the disk rotation below T g th erm al (her e T g,1 t h erm al )
has been r eported for DLCs. 37 , 64 According to the pictur e of molecular dynamics drawn for HAT 6
in ref. 49 discussed above, the only remaining unfrozen t y pe of movement below T g,1 th erm al i s
trans lational in - plane mo v ement s or small ang le rotational f luctuations of the trip hen y l ene co re.
Thus, α 2 -pr ocesses is attributed to the coopera t ive fluctuation s of tra nslational in - pla ne movements
and/or small angle rotationa l fluctuations of the triphen y l ene core insid e the columns, where
relatively distorted pac k ing of the cores leads to a frustration of the column packing . This
mol ecular assi gnm ent of α 2 - proc ess is illustrate d in Fi gu r e 31 d and the f rustration of the column
packi n g Fi gu re 2 b. Tr an s lati onal mo vemen ts o f th e cor e are rest ri cted b y t h e cor e - core di stan ce;
the dis tance bet ween t he adj acent cores in th e col u mns . T he rel ax ati on rat es of the α 2 - pro cess es
seem t o be co rrel ated wi th the co re - cor e di st ance (s ee Fi gur e 29 and T able 2). Since the columns

72

can be c onsi dered a one - dimensional liquid, the α 2 - processes can be cons id er ed as glass y d y nam ics
in a one-dimensional liquid.
Com pari ng the tem p eratu re d epend en ce o f the α 2 - p roces ses for t he S HU mat eria ls with that of
HAT5 (s ee F i gu re 29 ), i t rev eals t h at at the s am e t emp erat ure t h e rel ax ati on rat es fo r t he SHU
s y s tem s a re hi gh er th an that of HAT 5 . The α 2 - pro cess es are related to the disorder in the column,
therefore, it might be concluded that the disorder or distortions of the col umns are high er fo r th e
functionalized DL C s than that of HAT 5 .
4.1.4. Conclusions
Here, the m esom o rph ic p rop erti es, ph as e b ehavi or and m olecu la r d ynamics of a select ed seri es
of monofunctionalized triphen y len e - bas ed D LCs, SH U09 - SH U12 , were st udied. The obtained
resul ts w ere comp ared wi th that of t he com merci all y availabl e H AT5 , which is the corre spondi ng
unfunctionalized symmetrical DLC.
The mesomorphic properties we r e studied using POM as well as employing XRD, and
colu mnar m esop hases wer e rev ealed. Besi des the ch aract eris tic Br a gg peaks , a diffuse halo is
observed in the XRD pa ttern i ndi cates nan ophas e s ep arati on b et we en in t ercolu mnar a rea fil led
with the disordered f l ex ible alky l chains and columns built of the aromatic c ores.
The phase be h avior of the SH U09 - SH U12 compounds and HAT5 was investigated using
conventional DSC. Except for SHU12 , broadened temperature range of t he Col h m esop hase was
found for the other SHU mate rials compared to unfunctionalized HAT 5 . Thus, it is concluded that
mono functionalization of one of t he six alky l arms of H AT5 with ethy l gly c ol ate, hexanoyl, or
trifluo romethyl re sults in better sta bilization of the Col h mesophase, in contrast to the
func tionalization with di ethyle n egl y col. More ov er, two the rmal glass tra ns it ions, T g,1 ther ma l at high

73

temp eratur es and T g, 2 t h erma l at lo w tem pe ratures , wer e dete cted in the C ry phase for SHU09 ,
SHU11 , SHU12 as well as HAT 5 and in the Col h phase for S HU10 .
The mo lecul a r d ynamics were ex pl ored b y BDS. B eside s localized fluc tu ations, two process es
are det ected ( α 2 - and α 1 - relaxation), where the c o rresponding relaxation rates are both cur ved when
plotted versus inverse temperature indi cating glass y d y namics. The temperature de p endencies of
relax ati on rat es o f α 1 - pr oces ses a re further inves tigated using FSC . As a first result , th e data
obtained from B DS , FSC and conventional DSC corre spondin g T g,1 th er ma l agree wi th ea ch o ther,
and can be well described by a s ingle VTF dependenc y. This is found for all materials.
The α 1 - process is attributed to the coope r ative fluctuations of the alky chains in the
intercolumnar space, partl y coupled wit h small angle rotational fluctuations of the core. This
assi gnment is reas on ed b y the det ect ed PE - like gla ss y d y namic s for SHU compounds . Such an
assig nment of gla ss y d y n amics to PE - like glass y dyna mi cs has been reported for columnar
D LC s 33 , 40 and columnar ILC s 135 . Th e alk y l ch ains are a rran ged i n th e int erc olu mnar s pace b etw een
the s elf - assemble d columns of the aroma tic moieties whic h induces a spatial c onfinement to the
alk yl chai ns. Th ere fore, t he α 1 - process must be regarded as a glass transition in a three - dimensional
confinement.
At t emperat ur es l ower t han the ch ar act eris tic t e mperat ures fo r the α 1 - pro cess, the d iel ect ric
α 2 - proc ess w as found. Moreover, SHS was perfor med as a compl e mentary technique to BDS in
order t o in vest i gate the glass d ynam ics r elat ed t o α 2 - proc ess. Similar to the α 1 - proc ess, it is
concl uded t hat t he di elec tr ic and calori met ric dat a are in g ood a greem en t f or α 2 - processes. This
agreem ent evid en ces th e f act that t h e α 2 - process corresponds to a glass transition. At these
temperatures, the coope r ative fluctuations responsible for the α 1 - proc ess are frozen. The only

74

remaining un frozen t y p es of fluctuations are parallel and perpendicular movements (translational
movements) or small angle rota tional fluc tuations of the cores. Thus, α 2 - pr o cess is assi gned to the
coope rative fluctuation of translational in - pla ne movements and/or small angle r otational
fluctuations of the triphenylene core inside the part of columns, where a frustration of the column
packing is present. Because of the pre s ence of the certain amount of disorde r in the column, it can
be cons ider ed as a one- di mensional liquid. Because the α 2 - process is relate d onl y to the columns,
it can be considered a s a glass transition in a one-dimensional liquid.
I n summary, multip le glassy d y n amics in trip he nyle n e - based D LCs hav e been r ev ealed b y
combining BDS and advanced calorimetr y t echniques. The dipole functionalization of
triphe n y len e der iv atives ga v e possibility to p robe molec ular d y namics in deta il through d ipole
fluctuations perspec ti ve b y BDS. For unfunctionaliz ed tripheny l enes, it is difficult to distinguish
the dif ferent glassy dy namics, as it is in ca s e of H AT 5 , b y BDS due to the weak dipole movement.
On the other hand, a dvanced calorimetr y t echniques, FSC and SHS, probe g l assy dynamics
through the pe rsp ective of entrop y fluctuations. Thus, the combination of different technique s i s
ver y benef icial in o rder to understand and reveal a proce s s in a system from differe nt pe rspectives
in a co mpl ement ar y man ner.
4 .2 . Triphenylene Cro w n Ether - Bas e d D iscot ic Li quid Crystals
The ph ase beh avi or o f two u ns ymmetri cal t rip hen ylen e cro wn et her - based DLCs having
differe nt lengths of alkyl chains, K AL 465 and KAL468 (s ee Fi gu re 17a ), w as investig ated using
DSC. Two glass transitions were observed in the Cry phase b y D S C . The molecula r mobilit y of
the KAL compounds w as studi ed using BDS . In the BDS inve stigation s, t hree dielectric a ctive
relax ati on pro cesses wer e obs erved for both samples. At low temperatures, a γ - proce s s in the C r y

75

stat e was d ete cted an d is assigne d to the localized f luctuations tak in g pla ce in the alk yl chains. The
α 1 - process t akes p lace at h igher tem per atu res in the C r y ph ase. An α 3 - pro cess w as found in t h e
Col h mesophase . The temperat ure d epen d ence o f th e relax at ion rates of the α 3 - proce ss is a
comp letel y diff erent than that of the α 1 - relax ati on. Mol ecular ass ignm ent s o f t hese di ffe rent gl ass y
dyna m ics are proposed. T g th erm al determ ined b y DSC agrees with the dielectric data cor respondin g
to t he det ected gl ass y d ynamics . In addition, a c o nductivit y c ont ribution w as ex plo red b y BDS fo r
both KAL compounds . Th e conductivity contr i buti on appears in both Cry and Col h p hases at
temp eratur es above 300 K.
4.2.1. Phase Behavior
The phase be havior of th e KAL compounds w as ex plored by DSC ex peri ment s. The obtained
DSC ther mograms for KAL465 and KAL468 are given in Fi gu re 33a and b for th e first cooling
and the second heating run. T abl e 4 shows t h e es tim ated p hase tran si t ion temp eratur es and
enth alpi es det ermi ned to ge th er with the corresponding literature va lues.
A h y s ter esi s was obs erv ed bet ween t he cooli ng an d heat in g c ycles fo r th e phas e trans it ion
temp eratur es for bo th materi als . The h yste resi s for the C r y - Co l h tra ns ition is more pronounced
than that for the Col h - I so transition. On the one hand, the phase transition enthalpies of C ry -Col h
for K AL465 is higher than that for K AL 468 . On the other hand, the phase transition enthalpies of
Col h - I so are s imi lar fo r b oth KAL465 and KAL 468 . This might imply t hat long er alk y l chains
result in higher the enthalpies of Cr y -Col h tra nsition, althoug h, it seems to be the le n gth of alky l
chains has no significant effect on the enthalpies o f Col h - I so tr ansition for t hese two c ompounds.
Moreover, the sho rter alkyl chains lead to the broader temperature range of the mesophase ( 91 K
for KAL465 > 84 K for KAL468 ).

76

Figure 33 . DSC th er m o grams of (a) KAL 465 and ( b) KAL468 dur ing hea ti n g (r e d l ine) and c oo li ng (b lue li ne) wit h
a he ating/cool ing rat e of 10 K

mi n -1 . Da shed - dotted lines point out
the ph a se t ransiti on temper atures obs er ved du ring
the hea ti ng c yc le . D SC t her m o gra ms of ( c)

KAL465 a nd (d ) KAL468 zoom ing the temperature range between 175
K
and 475 K for th e heat ing run .

Black solid vertical li nes indi cate the determ i ned thermal transition tem per atures.

Table 4. P hase trans i tions temperatures and en t halpies determined by DSC
Co mpound

Run
T

g,1
thermal [K]
(∆c

p
[J K

-1
g

-1
])

T

g,3
thermal [K]
(∆c

p
[J K

-1
g

-1
])

Pha se
T [K ]
(∆H [J g

-1
])

Pha se

T [K ]
(∆H [J g

-1
])

Pha se
KAL465
2 nd H

202.9 (0. 05)

255.5 (0. 10)

Cr y

335. 8 (2 8.5)

Col

h

4 27 .3 (2. 2)

Iso

1 st C

-

-

Cr y

307. 4 ( 30. 1 )

Col

h

42 4.3 (2.2)

Iso

KAL468
2 nd H

195.4 (0. 06)

246.8 (0. 08)

Cr y

339.2 (3 3.4)

Col

h

42 2.8 (2. 4)

Iso

1 st C

-

-

Cr y

317.3 (3 9.6 )

Col

h

4 19 .1 ( 2. 2)

Iso

KAL465 *
2 nd H

-

-

Cr y

329.2 (2 8.3)

Col

h

426.2 (1. 8)

Iso

1 st C - - Cr y 310.2 (3 3.4) Col h 416.2 (1. 4) Iso
KAL468 *
2 nd H

-

-

Cr y

338.2 (3 2.4)

Col h

422.2 (2. 4)

Iso

1 st C

-

-

Cr y

321.2 (3 7.1)

Col

h

421.2 (1. 9)

Iso

H: Heating, C: Coo ling. * The data was t a ken from ref. 132 for com parison .

(a)

(b)

(c)

(d)

77

Two di fferen t step s observed in the temperature dependence of the he at flo ws shown in Fi gu re
33 i n the Cry phase for both compounds indicat e two thermal g lass transition s . The mid - st ep
positions of the steps we re taken as T g, 1 th er ma l and T g, 3 th erm al for the glass transition s at higher and
lower t emp erat ures res pe ctiv el y . The dete rmined therma l glass transition tempera tures ( T g,1 th er ma l
and T g, 3 th er ma l ) as wel l as corres pon din g Δc p values are giv en in T able 4. These glass tr ansition
impl yi n g some disorder in th e materia l m ight be caused by a kind of nanophase separation of the
alk yl chain s and the aro m atic core s. S uch a nanopha s e separation was evide nced b y an amorphous
halo observed in the X-ray patte rns of the di ff eren t C LC s in the Cr y phase. 21 , 25 , 37 , 135 Additionall y ,
a step - lik e chan g e in t he t emp eratu re d ep enden ce o f t he h eat fl ows , in t he te mp erature ran ge fro m
365 K to 240 K, is observed in the Col h phase for both KAL465 and K AL468 . Althou gh, i t mig ht
impl y a columna r ther mal g lass transition , the re p roducibilit y of the data for this step is
questionable. A more detailed investig ation b y means of SHS and/or FSC is needed to evidence
that it is a glass tra nsition; theref or e, it is not furthe r discussed here .
4.2.2. Molecular Mobility
The mo lecul ar d y nam ics of t he tripheny lene cro wn et her - b ased u ns y m m etri cal D LCs w ere
investig ated using BD S . The BD S i nves ti gati ons are shown in Fi gure 34 in 3D repr esent ati on s of
the d ielect ric l oss spect r a as a fun cti on o f fr eque nc y and tem per atu re. th ree d iel ect rical l y active
T processe s denote d a s γ - , α 3 - and α 1 - relax at ion are o bserv ed . In the Cry pha s e, the γ - proces s
appears at low temper atu res and α 1 - process at higher temperatures. α 3 - pro c ess is obser v ed at even
higher t emperatures in the Col h mesoph ase. In a dd iti on, a conductivity contributi on is detected at
low freque n cies and high t emperatures in the Cry and Col h ph ases.

78

Figure 34 . 3D r epresentation of the dielectric loss as fu nc tion of frequen c y and tem p erature for (a) KAL46 5 and
(b)

KAL468 for the sec o nd he a ti ng r u n. Arro ws i ndicate the dielectric processes and the co nd uc ti vit y c ont ri b uti on .

Figure 35 . Temperatu re d ependence of th e dielectric loss (log 𝜀𝜀 ′′ ) at 1000 Hz f or (a) KAL 465 and ( b) KAL 468 fo r
the se co nd he a ti ng r un. D as he d li nes p oi nt o ut t he p ha se tra nsiti on t e mp er atur e s d et ec ted d urin g t he he at i ng c ycle as
indicated .

Fi gu r e 35 depict s the ov erview of the BDS measu rement s fo r the s econd heating run,
repres ent ed as the t em per atu re d epend en ce o f the d iel ectri c lo ss (log 𝜀𝜀 ′′ ) at 1000 Hz, KAL465 and
KAL468 . Th e observed sh arp ch an ge s in t he t em peratu r e dep enden ce o f t he ε″ for both samples
at tem perat ur es clo se to the C ol h - Is o phase transition temperature (T Colh - Is o ) could be further taken
as a m easure fo r the pha se tra nsition temperatur es . The T Colh - Iso determined b y DSC is in good
α 1

α 3

Cond uct ivit y

γ

(a)

(b)

(a)

(b)

79

agreem ent wit h th e T Colh - Is o obtained from the diel ectri c data . As i t i s revealed b y DS C, a
pronounced thermal h y st eresis was al so o bserv ed in t he di electr ic dat a fo r t he Col h - Is o tra nsition .

Figure 36 . Frequen c y dependency of dielectric loss for the γ - processes of (a) KAL 465 and (b) KAL4 68 as w ell as
that for the α

1 - and α 3 - process es of (c) KAL 465 and (d) KAL468 .
T he HN -function (eqn. (13) ) was fit ted to th e data i n or der to anal y z e the rel ax ati on p rocess es
quantitatively. E x ampl es of the HN -funct io n f ittings to the d ielect ric p ro cesse s are shown for
KAL465 and KAL468 in Fi gur e 36. Th e rel ax at ion rates 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 obtained from t he fits for each
temp eratur e, a re co ll ecte d in the relaxation map giv en in Fi gu r e 37 . Similar to the case of SHU
compound in the previous section , the die le ctric d at a o f PE are added to Fi gur e 37 for comparison
since the re pe ating units of PE hav e a com pa rable st ruct ure to the st ructure of the alky l substituen ts
of KAL compounds. T herefore, such a comparison of the temperature dependencies of the
(a)

(b)

(c)

(d)

80

relax ati on rat es 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 o f t he rel ax ati ons proces ses for PE and that fo r CLCs h aving substituent
alk yl chains seems to b e useful in o rder to assi gn the d etect ed pro ces s es to the m olecu lar
fluctuations.
2 3 4 5 6 7 8
-4
-2
0
2
4
6
8
PE
α 1
log f [Hz]
1000/T [K
-1
]
γ -relaxations
α 3
KAL465
KAL468
Cry
Col
h

Figure 37 . Rel axation map of KAL465 and KAL 468 . Open red sym bols – d ata for KAL 465 ; ope n blue sym bol s –
data for

KAL468 . S q uares – γ - relaxat ion (B DS); tria ngle s – α 1 - relaxatio n (B DS); cir cles – α 3 - relaxatio n (BDS);
filled
star s

– thermal g lass transition tem peratures (DSC). The relaxat ion rates were calcu lated b y eqn . ( 3) for
the gi ven DS C
data.

Solid lines are the fits of the VFT - equa t io n (eq n. (2) ) to the d a ta. Da s hed line s ar e the fits o f Arr he ni us -
equatio n
(e qn.

(1) ) to the data. F illed black circles and squares indicate the dielectric α - and γ - r ela xatio ns of PE
ta ke n fr o m t he
re f.s

145 and 40 respectively .
The tem per ature dep end ence o f the relax at ion rat es of th e γ - r elax at ion was appro x im ated b y
the Arrhe ni us equation ( eqn. (1)). As i t h as bee n rev ealed fo r SHU compounds, simi larly the
γ - process of KAL comp ounds is assigned to the localiz ed fluctuations tak ing place in the alky l
chain s si nce t h e temp erat ure depen de nces of t he rel ax ati on rat es of the γ - pr ocess es for KAL465
and KAL468 are quite similar to tha t for PE . 40 Fu rth ermore, t he t em peratu r e d ependen c es of the
relax ati on rat es o f th e γ - p rocess es for KAL com pounds and that for HAT5 (as wel l as th at f or
SHU09 -12 ) cl osel y resem bl e each ot h er (s ee F i gu re S 30). The acti vat i on en ergies fo r the
γ - relax ati ons are cal culat ed t o be and 2 9 kJ m ol -1 for KAL 4 6 5 and 28 kJ mol -1 for KAL 46 8 (see
Appendix I II , T abl e S 2 ). Mo reove r, t he rel ax ati on rat es o f the γ - process of KAL465 are hi gher

81

than that of KAL468 , although as reported in r ef. 132 the lattice spacing o f the columns in Col h
phase i s s mall er for KAL465 than that for KAL 46 8 . F or SHU compounds, a linear relation of the
latt ice s pacin gs and 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 of γ - process es h as been r eali z ed and ex plained b y the self -conf inement
effect . However, such a relation is not recognized for the KAL compounds.
The tem perat u re dep end en cies of the r elax ati on rates of the α 1 - and α 3 - relaxations are curv ed
when they are plotted in the r elaxation map, indicatin g glassy dy namics. Ther efor e, th e y are
approx i mat ed b y the V F T -equation ( eqn. (2 )) . Th e cal cul ated V FT p aram e ters ar e s umm ariz ed i n
Table S 2. Th e rel ax ati on rat es co rresp ond in g to t h e T g,1 t her ma l and T g, 3 t h erm al obtained b y DSC were
calcul ated b y eq n. (3) , and is added to Fi gur e 37. On the one hand, t he rel a x atio n rates relat ed to
the T g, 1 ther ma l estimated by DSC is a good ag reement with dielectr ic α 1 - proces ses. On the other
hand, t he r elax ati on rates o f d ielect ric α 3 - process es det ected i n th e Col h m esopha se almost compl y
well w ith the calorimetr i c data for T g, 3 th er ma l det ect ed in the C r y phas e. Ho wever, t he comparison
of th e temp erat ur e dep en d encies of the di el ectr ic and the rmal relaxation rate s of the α 1 - proces ses
eluci dated that α 3 - pro ces ses s eem to have f aster dy n amics in Cr y phase than that in the Col h ph ase.
In or d er to get more understanding of the reason of t his dis crepanc y , the glass dy namics relat ed to
th e α 3 - proc ess es should be further studied using the calorim etri c t echni ques like SHS and/or FSC .
The tem perat ur e depen d en cies o f the rel ax ati on rat e of t he α 1 - proces s es for KA L compounds
is similar to that for the dielectric α - pro cess of PE . M oreov er , the dat a for t he calori met ri c
α -process of PE 146 a nd t he PE - l ike glass y d y n am ics d etect ed for pol y(n- decy l met h acr ylat e) 147 as
well as th e d ata fo r α 1 - p ro cess o f HAT5 o verl ap wi th t he di elect ric d at a mea sur ed for α 1 - pro cess es
of KAL compounds (se e Fi gu r e S 30 ). Fo r this reason, the α 1 - process es of KAL465 and KAL468
are attribute d to the PE - like cooperative fluctuations of the alk yl cha i ns. S imilar PE - like g lass y

82

d y n amics repo rted for S HU compounds ( S ection 4.1.3 ) 43 , tripheny l ene - bas ed 40 , 144 and
p yr e n e - based D LCs 33 further pr oof this assignment.
The α 3 - pro cesses o f the KAL compounds were obs erved ( in the Col h phase) at t emper at ures
higher th an th e t emperat u res wh er e t h e α 1 -process es were d ete cted ( in the Cry phase ). This implies
that molecular origins are presumabl y dif ferent for the α 1 - and α 3 - proces ses. For the m ol ecular
assignment of the α 3 - pro cess, the molecular motions of the molecules of t he tripheny lene - bas ed
D LC s discussed in the S ection 4.1.3 should be considered (see Figu re 31 ). This is because the
molecular motions of the molecules of t he KAL c ompounds are expected to be simila r to that of
the trip henyle n e - based DLCs owing to the pre sen ce of tripheny l ene groups also in the core of the
mol ecules of KAL465 and KAL468 (s ee Fi gu r e 16 and F i gu re 17 a) . After assigning the
α 1 - processes t o t he PE - li ke glass y d y nam ics o f th e alk yl chains, according the discussions in the
Section 4.1.3 the remainin g interp retation possibility for the molecular a ssignment is the
coopera t ive fluctuations of the molecules of the core; tr anslational in - pla ne movements and/or
small an gle rota tional fluctu ations . T he temp erat ure d ependen ci es o f the rel ax ati on rat es of t he
α 2 - processes detected in the Cry phas e for SHU09 , SH U12 and HAT5 are similar to that f or
α 3 - processes of the KAL465 and KAL468 . The r efore, the α 3 - processes of KAL465 a nd KAL468
might be assigned to the coopera ti ve fluctuations of the cores made of triphenylenes including the
crown ethe r groups. For this interpre tation, it sho uld be considered that int erconnected columnar
stru cture f or med b y t he KAL compounds mi gh t r esult in hig her restr ictions on the glas s d ynamics
attributed to the core . Thi s might ex plain wh y t he α 3 - proces ses w ere d et ected at tem peratu res
approx i mat el y 180 K higher than t he tem per ature wh ere α 2 -process es w er e obs erv ed . Although,
this interpr etation possibilit y se ems to be likel y , also dif ferent inter p retation possibilitie s might be
discussed. A not her possibilit y for the molecular assig nment of the α 3 - process might be t he

83

coopera t ive fluctuations of the crown ether ( sinc e th e cro wn et her car ries a considerable di pole
moment ) or rotational fluctuations. T he understanding gained here b y BDS is insuf ficient to furthe r
discuss the interpre tation possibilities for the molec ular assignment of the α 3 - pro cess without any
furt her investi ga t ions, e.g. S HS and/or FSC investigations.
4.2.3. Conductivity
The dielectric sp ect ra a r e dom in ated b y conductivit y cont ribution at t he tem perat ur es above
300 K for KAL465 and KAL468 . The conductivity c ont ributions obs erv ed were als o anal y z ed to
quantify the condu ctivity contribution as well as to reveal the c onducti vit y m echanism. The
complex conductivit y 𝜎𝜎 ∗ is relate d to the co mpl ex dielect ric fun ct io n 𝜀𝜀 ∗ through the relationships
given in eqn.s (20), (21) and (22). Fi gu re 38 d epict s fr equen c y dep end en cies of t he 𝜎𝜎 ′ for KAL465
and KAL468 at differ ent tem peratu res in the Cry phase and the Col h phase. As it is di scussed in
the Section 3.1.1 and also shown in Figu r e 10, the fre quenc y dependenc e of t he 𝜎𝜎 ′ g iven in Fi gur e
38 shows the t y pical beh avior of semiconducting disordered materials . F or such a behavior , the
plateau value s correspon d to th e DC conductivit y ( 𝜎𝜎 𝐷𝐷𝐶𝐶 ).

Figure 38 . Frequency dependence of the σ′ at the i ndicated t emperatures for the s econd heating run; (a) KAL 465 and
(b) KAL468 . Dashed lines i ndicate the plateau corresponding to th e D C conductivity.

(a)

(b)

84

Jons ch er -equation (eqn. ( 23) ) was us ed to d es cribe the frequenc y d ependencies of the 𝜎𝜎 ′ gi v en
in Figu re 38. The temper at ure depen d ence of the 𝜎𝜎 𝐷𝐷𝐶𝐶 is s hown in Figu r e 39 , which c onstructed b y
the 𝜎𝜎 𝐷𝐷𝐶𝐶 estimated using Jonscher -equation. Th e phase transitio n for t he C r y -Col h transition were
reco gniz ed as a chan ge i n t he tem perat ur e depe nd ence o f th e 𝜎𝜎 𝐷𝐷𝐶𝐶 .

Figure 39 . DC cond ucti vit y 𝜎𝜎 𝐷𝐷𝐶𝐶

for (a) KAL465 and (b) KAL 468 versus inverse temperature. T he dashed - dotted li ne
indicates

the phase transiti o n temperatures f or the heating cycle as i ndicated.
Solid black lines are the fits o f
Arrhe nius

- equatio n (eq n. (1)) to the data.
As it has been reveal ed b y DSC, a h yster esis betw een heat in g and coo li ng runs w ere al so
reco gniz ed fo rm t he t em peratu r e dep enden ce o f t he 𝜎𝜎 𝐷𝐷𝐶𝐶 for both materials. Moreover, the ph ase
trans ition tempera tures for the Cry -Col h transition observe d i n the dependency of 𝜎𝜎 𝐷𝐷𝐶𝐶 agre e wit h
those determined using DSC. In the Cry pha se, the values of the 𝜎𝜎 𝐷𝐷𝐶𝐶 ar e low compared to the
values in the Col h mesophase. Upon transition from the Cry phase to the Col h mes o phase, the
values of the 𝜎𝜎 𝐷𝐷𝐶𝐶 ch an ges b y appro x im atel y 1 ord ers of magnitude . The 𝜎𝜎 𝐷𝐷𝐶𝐶 val ues determined for
KAL465 and KAL468 are t y pical fo r triphenyle ne - based D LCs (se e Fi gure S 31 for th e
comparison of the 𝜎𝜎 𝐷𝐷𝐶𝐶 for KAL and SHU compounds as well as HAT6 ). 14 7F
148 Sin ce the similar
values of the 𝜎𝜎 𝐷𝐷𝐶𝐶 found for KA L an d SHU compounds as well as HAT 6 (se e Fi gur e S 31 ), it is
assu med for KAL465 and KAL468 tha t t he mai n conduction mechanism might b e due to the
(a)

(b)

85

delo caliz ed ele ct rons o f t h e π - π st ack ed ar omat ic cores . As it can b e b ette r s eem in F i gu re S 31 , it
is real iz ed t hat t he val ues o f the 𝜎𝜎 𝐷𝐷𝐶𝐶 for KAL465 is sligh tl y hi gher than that for KAL468 . For
D LC s , t he disc mobilit y as well a s the mobility o f the alky l chains might af fect the char ge ca rri er
mobilit y . 33 , 39 T hus, this mig ht be interp reted as th e shorter alk y l chains resul t in higher 𝜎𝜎 𝐷𝐷𝐶𝐶 for th e
KAL compounds, s ince the onl y differen ce betw een KAL465 and KAL468 in t he chem ical
structure of the i r molecul es is the le ngth of the a lk y l chains .
In both Cr y and Col h phases, t he t empe rat ur e dep en dence of t he DC condu ct iv it y was des c ribed
by Arrhenius - e qu ation (eqn. (1) ) for bot h materials. I n both phases, activation energies of
80 kJ mol -1 for KAL465 and 83 k J mol -1 for KAL468 were esti mat ed. This im plies for both
materi al s si milar restrictions on the charge transport unex p ectedl y for both phases and/or no
change in the conduction mechanism upon Cry- C ol h phase transition.
4.2.4. Conclusion
Two un s ymmet rical trip h en ylene crown et her - based DLCs having different lengths of th e a lk yl
chain s were investigated using DSC and BDS . The p has e beh av ior o f KAL465 and KAL468 was
explored b y DSC. Two thermal g lass transitio n ( T g,1 th erma l and T g,3 t h erma l ) were detected for both
materials in the Cry pha se. In addition, one thermal glass tra ns ition was found for both KAL
compounds in the Colh mesophase.
Besides the c ondu ctivit y contribution detected , th ree di ele ctri c act ive r el ax atio n pro cesses
were p robed fo r both sampl es. At low temperatur es in the Cry stat e , t he γ - process w as det ect ed ,
and is assigned to the PE - like localized fluctuations taking plac e in the alkyl c h ains. On the
contrary to the SHU c ompounds, the s elf - confinement effect is not observed f o r the KA L
compounds since the calculated activation energies for the γ - pro ces s are sim ilar for both KAL465

86

and KAL468 . Mo reov er, a li near rel ati on of t he l atti ce spaci n gs and t he 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 of the γ - pro ces ses
are not reco gn i z ed , the refore, it is concluded that l ength of the alkyl chains has no considerable
effect on these localized d y namics.
Multiple g lassy d y namics were probed for bo th m ateria ls b y BDS; α 1 - pro ce ss in the Cry phase
and α 3 - process in the Col h mesophase. Th e p robed glassy dynamics have different temp er atur e
depend en ce of th e rela x ati on tim es , consequently, differ ent m ol ecular ass ignmen ts o f th ese
differen t glass y d y nami c s have been p roposed. On the one hand, the α 1 - pr o cesses o f KAL465 an d
KAL468 are assign ed to t he PE - like cooperative fluctuations t aking place in the alk yl chains, s ince
the t emperat ure dep en de nce of t he rel ax atio n rat es of the α 1 - proc ess is quite similar to that of PE
as well as that of S H U09 , SHU1 0 and H AT5 . O n t he other hand, the α 3 - proc ess of the KAL
compounds might be am biguousl y attributed to t he cooperative fluctuations of the cores, where
each core consists of two triphen y len es connected to each other through the crown ether. For m or e
ambiguous molecular assignment o f the α 3 - process , it is concluded that further investi gations are
requi red . Furth erm ore, d i electr ic dat a corresponding to the α 1 - and α 3 - processes ag rees w ith t he
calori met ric dat a ( the T g, 1 th erm a l and T g,3 th erm a l probed by DSC ).
Besides t he m ole cul ar d ynam ics , a conductivit y pr ocess was also ex plored b y BDS fo r both
mater ials. This proc ess appears at even higher temperatures than the probed relaxation processes.
T he values of the 𝜎𝜎 𝐷𝐷𝐶𝐶 were estimated usin g Jonscher- equation from the f requenc y dep endenc y of
the σ ′ . Accord in g to t he ob tai ned t emperat u re dep en den cies o f th e 𝜎𝜎 𝐷𝐷𝐶𝐶 for KAL 4 6 5 and KAL468 ,
it is concluded that t he determined 𝜎𝜎 𝐷𝐷𝐶𝐶 val ues are t ypic al for trip hen ylene - b ased D L Cs. Moreov er,
it is concluded that the delocal iz ed el ectron s o f th e π - π s ta cked arom ati c c ores mig ht be the main
conduction mecha ni sm i n both Cr y and Col h ph ases.

87

4 .3 . Ion ic L iquid Cr ysta ls
This sect ion i s reproduced/adapted f rom A. Yildirim, P . Szy moni ak, K. Sentker, M. Butschies,
A. Bühlmeyer, P. Huber, S. Laschat, A. Schönhals, Dynamics and ionic conductivity of ionic
liquid crystals forming a hexagonal columnar mesophase, Ph ys. Ch em. Chem . Ph ys. 2018 , 20,
5626 − 5635, with pe rmission from the P CC P O wner S ociet ies ( DOI:
https://doi.org/10.1039/C7CP08186C ).
For the first time , the molecular mobilit y o f two linear - s hap ed tet r amet h y l ated guani din ium
trifla te IL Cs having differ ent length s of al k yl ch ains , LC536 and LC537 (s ee Fi gu re 18 a) , was
investigated by a combi nation of BDS and SHS. B y se lf - ass embl y , thes e ILCs can form a Col h
meso phas e besi des Cr y phases and Iso liquid stat e. Three d iel ect ric act ive pro cesses w ere foun d
by B DS for both sample s. At low temperatures, a γ - process in the Cr y state i s o bserv ed which is
assigne d t o localized fluctuations of methyl gr ou ps including nitrogen a t oms in the guanidinium
head. At higher temperatures but still i n the C r y s tate, an α 4 - pro ces s t ak es pl ace. An α 1 -process
was det ect ed b y SHS bu t wit h a comp let el y diff e rent t empe rat ure dep end en ce o f th e r elax at ion
times than that of the α 4 - relaxation. This result is discussed in detail, and different molecular
assi gnment s of t he pro ce ss es are s u ggested . At ev en h ighe r tem per atures , elect ric al co nduct ivi t y
is detected a nd an increase in the DC conductivity b y four orders of magnitude at the pha se
trans ition from the Cry t o the Col h mesophase is found. This result is traced to a change in the
charge transport mechanism from a delocalized electron hopping in the stacke d aromatic syste ms
(in the Cry ph ase) to one dominated by ionic conduction in the quasi - 1D ion cha nnels formed
along the s upramolecular columns in the ILCs’ Col h mesoph ases.

88

4.3.1. Phase Behavior
Fi gu r e 40 a and b show t he DSC thermograms for L C536 and LC537 for the second heating
and the cooling c y cl e. The phas e transition temperatures were estim ated from the maximum
positions of the peaks in the heat flow, give n i n Tab le 5.

Figure 40 . DSC th er mograms of (a) LC536 and (b) LC53 7 d ur ing hea t in g (r ed li ne) an d co o ling ( bl ue l ine) wit h a
hea ting/ cooling rate of 10 K min

-1 . Dashed - dotted
line s po i nt o ut the phase t ra ns iti on t e mpe r a tur es o b ser ved d uri n g t he
heat i ng c ycl e. DSC t her mo gr a ms o f (c )

LC536 and (d) LC 537
giv en in the t e mperature range between 19 5 K and 285
K fo r the hea t in g ru n.

(a)

(b)

(c)

(d)

89

Table 5. P hases an d phase transitions temperatures deter m i ned b y DSC and B DS
Co mpound

Run
Pha ses a nd Tra n siti ons T [K ]

DSC

BDS

LC536
1 st Cooling

Cr y

1
295 Col

h
408 Is o

Cr y

1
301 Col

h

2 nd Heating

Cr y

1
309 Cry

2
330 Col

h
411 I so

Cr y

1
309 Cry

2
327 Col

h

2 nd Heating*

Cr y

1
310 Cry

2
324 Col

h
419 I so

-
LC537
1 st Cooling

Cr y

1
313 Col

h
420 Is o

Cr y

1
322 Col

h

2 nd Heating

Cr y

1
325 Cry

2
336 Col

h
423 I so

Cr y

1
324 Cry

2
337 Col

h

2 nd Heating*

Cr y

1
323 Cry

2
338 Col

h
429 I so

-

*DS C r esu lt s ta ke n fr o m re f. 134 .

A h y s t eresi s w as o bserv ed betw een t he cool in g and h eati n g c ycles. Th e h yster esis for th e
transition from the Cry to the Col h phase is m ore pronounced than that for the tra ns ition from the
Col h mesophase to the Iso phase. The phase tr ansiti on enthalpies of Cry 1 - Cr y 2 (32.6 J g -1 fo r
LC536 ; 45.8 J g -1 for LC537 ) and Cr y 2 -Col h (31.6 J g -1 for LC536 ; 0.7 J g -1 for LC537 ) transition
are hig h er than the enthalpy of Col h - I so (0.7 J g -1 for LC536 ; 0.6 J g -1 for LC537 ) transition. This
is expected due to larger structural changes taking place during the f i rst two transitions. M oreover,
the C r y 1 - Cr y 2 transiti on appears only upon heating, and therefore the corresponding phase is
thermo d y n amically me tastable. 78
A step observed in the tempera t ure range between 195 K and 285 K is observed indica ti ng a
therma l glass tr ansition ( see F i gu r e 40 c and d ). T he T g t h erma l wer e det ermi n e d from the mid - s t ep
position and found to be 242 K for LC536 and 248 K f or LC537 . The Δc p f or the ther mal glas s
trans ition s w ere found to be 0.33 J K -1 g -1 fo r LC53 6 and 0.27 J K -1 g -1 for LC537 . For a materi al,
underg oin g a gla ss tr ansition implie s some di sorder in the m aterial. Disorder in LC536 and L C537
leading t o the glass tra nsi ti on might be ca us ed by a kind of nanopha se separation of the alky l ch ain
and the aroma t ic parts of the IL C in the Cry 1 phase. Such a nanopha se s eparation, reported for a

90

series of triphen y lene - b as ed D LC s , was evidence d by an amorphous halo observe d in t he X - ra y
patt erns o f thes e D LCs. 21
4.3.2. Molecular Mobility
Fi gu r e 41 depi cts 3 D rep r esent atio ns o f the d iel ect ric l oss spect ra as a fun ct io n of freq uen c y
and temperature for the second heatin g run for L C536 and LC537 . Two dielec tricall y active
proces ses can b e i dent ifi ed as peak s, label ed; γ - a nd α 4 - proces ses. Bot h rel ax at ion proces ses t ake
place i n th e Cr y 1 phase. At low t emperatures (or high fr equencies), the γ - p rocess app ears, wh il e
the α 4 - proce ss is observed at hi gher temperatures (or lower frequencies) tha n t hat for t he γ - p rocess .
The conductivity contrib ution appears at even higher temperatures.

Figure 41 . 3D representation o f the dielectric lo ss (log 𝜀𝜀 ′′ ) as a fun ctio n of frequ e ncy and temp erature for th e second
heat i ng r un; ( a)

LC536 a nd (b) LC537 .
Fi gu r e 42 d epi cts the t em perat ur e depen d enc e of t he d iel ectri c (lo g ε ′′ ) a t 1000 Hz , for LC536
and L C537 . No significant difference s b etween heating and cooling runs were observed in the
temp eratur e ran ge of t he plas ti c crystall in e phase. H owever, a sud den cha nge in the t emp eratur e
dependence of the di electric loss is observe d for both samples at temperature s close t o th e phase
transition t emperatur es. These changes in the t emperature dependence of ε″ could be further used
to dete rmine the pha s e transition te mperatur es fro m the die lectric meas urements in addition to the
Cond uct ivit y

γ

(a)

(b)

α 4

91

DSC data . Th e p has e tr a ns iti on t emp erat ures found in the diele ctric data agree with the tra nsition
temperatures determined b y DSC. L i ke for the DS C ex periments, a pronounced thermal h y st eresis
was ob served in the dielectric d ata for the tr ansition f rom the plastic cr y stalline pha se to the Col h
phase. Fur the rmore, the Cr y 1 - Cry 2 transition was observed onl y upon heati ng like for t he DSC
investig ations.

Figure 42 . Tem perat ure dependence of t he dielectric loss (lo g 𝜀𝜀 ′′ ) at 10 00 Hz f or (a) L C536 and (b) LC537 for the
heat i ng and co o ling r u ns.

Da s hed -
dotte d lines point o ut the phase transitio n temperature s de tected d uring the heating
cycle as indicat ed .

For the qua nt itative analy s is of the relaxation processes, the model function of HN -function ,
given in eqn. (13), w as fitted to the d ata. As an ex amp le, F i gu r e 43 illustrate s the fit of the
HN - function to the data of LC536 in the t emp erat ure ran ge o f th e γ - process. An example for the
anal y s is o f the d ata for LC 537 is give n i n Appendix IV in Fi gur e S32. F rom the fits, the relaxation
rate 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 is o btai ned as t he max imum posit ion of the die le ctric loss. In Fi gur e 44 th e r el ax atio n
rates 𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚 are plotted versus inverse temperature in the relaxation map for both LC536 a nd L C537 .
The temper at ure d epe n dence of t he rel ax at io n rates of γ - rel ax at ion can b e des cri bed b y
Arrhenius-equation (eqn. (1)).
(a)

(b)

92

-1 0 1 2 3 4 5 6 7
-2.2
-2.1
-2.0
-1.9
-1.8
-1.7
-1.6
133 K
153 K
log ε ''
log (f [Hz])
173 K

Figure 43 . Frequen c y dependency of dielectric loss for LC536 for the second heating at the indicated temperatures
(γ

- proce ss). Solid lines are the fits o f the HN - func t io n to the d at a .
The tem pe ratu re d ep ende nce o f r el ax atio n rates du e to loc al iz ed molecula r fluctuation f ollows
general l y the Ar rhen ius -equation (eqn. (1)). H ere f or t he act ivat ion ener g y of γ - relaxation for both
LC536 and LC537 , a val ue of ca. 33 kJ mol -1 i s found. Because no dependence of the activation
energy on the number of carbon atoms in the su bstituent is observed, the γ - relaxation of both
LC536 and LC537 is assig ned to the lo calized flu ctuations of th e ni trog en atoms in the
gua ni dinium head including the meth y l groups. This is in good ag reement with the lit erature values
for activation energies of localiz ed fluctuations of polar groups bonded to m ethyl
groups. 33 , 40 ,
148F
149 ,
149F
150 Moreover, the temper atur e d ependen ce of th e relax at ion rates of the γ - p ro cess
of our IL Cs is quite similar to that of the γ - process of PE . 40 T he diel ectri c γ - relax at ion of PE tak en
from ref. 40 is i ncluded in Fi gu re 44 for comparison.

93

345678
-2
0
2
4
6
α
1
α
α -relaxations
SHS
log(f
max
[Hz])
1000 / T [K
-1
]
BDS
α 4
γ
-relaxations
LC536
LC537
PE

Figure 44 . Relaxation map of LC536 and LC 537 . Fill ed red s ym bol s – data for LC536 ; O pen blu e sym bols – data
for

LC537 . S q uares – γ - relaxation ; st ars – α 4 - relaxat io n ; circles ( AC - chip calorimetry ) and triangles (TMDSC) – α 1
-
relaxati on

. Solid lines are the fits of VFT - equation (e q n. (2)) to the data. Dashed line is the fit of the Arr he ni us -
equation
(e qn.

(1)) to th e data of the γ - relaxation . Da shed - dotte d line d enotes the dielec tric α -
relax a tion of poly et hyl ene tak en
fro m r e f.

145 . Black hex a gons s ym bo lize the dielectric γ - relaxati o n of PE take n fro m r ef . 40 .
Fi gu r e 42 shows t hat compared to the γ - relax at ion the α 4 - process is quite broad. Therefore, in
addition to the anal y sis o f the α 4 - proce ss b y fitting t he HN - function to the data, it was also anal y z ed
b y a deri v ati ve - based an al ysis technique gi v en b y eqn. (18). For the HN - function, one obtains
eqn. (19). F i gu re 45 demonstrate s the fit of the deriv ative of the HN - function (eqn. (19) ) to the
𝜀𝜀 𝑑𝑑𝑑𝑑 𝑑𝑑 𝑖𝑖𝑑𝑑
′′ data o f LC536 in th e temperature r an ge o f the α 4 - proces s. T he tem per atu re depend en ce o f
the rel ax ati on rat es of t h e α 4 - relaxations is curved when plotted versus inverse temperature,
indicating of gla ss y d ynamics (α - relaxation) . I t is descri bed b y t he VFT -equation (eqn. (2)).

94

-2 -1 0123456
-2.2
-2.0
-1.8
-1.6
-2 -1 0123456
-2.2
-2.0
-1.8
-1.6
log (f [Hz])
log ε ''
257 K
249 K
243 K
251 K
243 K
235 K
log ε ''
deriv

log (f [Hz])

Figure 45 . Frequency dependency of (a) log ε″ and (b) 𝜀𝜀 𝑑𝑑𝑑𝑑𝑑𝑑𝑖𝑖𝑑𝑑
′′

of LC 536 for t he second heating at the indicated
temperatures (

α 4 - process). Solid lines are the fits of the e qn. ( 19 ) to the data.
The tem per atu re d epend e nce o f t he relax at ion rate s of the α 4 - relax ati on o f L C536 and LC537
measu red b y BDS h a s to be described b y the VFT - equation w hich might ind icate g l assy dy n amics
also for the ILC s . The est im ated VFT pa ramet ers are s umm ariz ed i n Tab le 6 .
Table 6 . VFT para met er s obtained from the BDS a nd SHS d ata. To reduce the number of free fit parameters, log f ∞
w a s fix ed to 8.
Co mpound

Run
BDS

SHS

log (f

∞
[H z ])

D

T

o
[K]

log (f

∞
[H z ])

D

T

o
[K]

LC536
Cool ing

8

2.8

133 ± 10

8

0.3

224 ± 5

Heating

8

2.9

130 ± 10

8

0.3

220 ± 5

LC536
Cool ing

8

3.1

140 ± 10

8

0.3

229 ± 5

Heating

8

2.6

130 ± 10

8

0.1

241 ± 5

(a)

(b)

95

In addition to BDS sensing di pole fluctuation s, SHS was carrie d out to investig ate the glassy
dyna m ics from the perspective of entropy fluctuations. A simi lar combination of methods was
applie d for low mole cular we i ght liquid c rysta l s y stems 33 ,
150F
151 and a pol y meric liquid cry stalline
s ys t e m 151 F
152 . For AC - chip calorime tr y , the rea l part of the complex diff erential voltag e, U R , can b e
taken as a me asu re o f the real pa rt of the co mpl ex heat cap aci t y . Tem pe ratu re d epend enc es o f U R
obtained by S HS carried out by differential AC - chip calor imetry f o r LC536 are giv en i n Fi gu r e
46 a for four measu red frequencie s . For lower frequencies than covered by AC - chip calor imetr y ,
SHS is carried out b y T MDSC. Fi gu r e 46b gives the temperature dependence of the 𝑐𝑐 𝑝𝑝 ′ at a
freque n c y of 5.6 x 10 -2 Hz . The temperature dependencies of both U R an d 𝑐𝑐 𝑝𝑝 ′ show a s tep - like
increas e w ith increas in g t emp eratur e wh ich i s cha ract eri st ic for a glass trans ition. Moreover, the
step s sh ift t o hi gher tem p eratur es wit h in creas ing fr equenc y as ex pect ed . 33 , 12 6
Both s ets o f SHS dat a were an al yzed b y tak in g ei ther t he m id - step position of U R (T ) or of
𝑐𝑐 𝑝𝑝 ′ (T) to deter m ine a correspondi ng dynamic gla ss T g dy namic f or the given frequency . 33 , 149 T h e
dy namic glass transition tempera tures obtained fr o m this analy sis together with the corresponding
measu red fr equen ci es ar e in clud ed in Fi gur e 44 (relaxation map) combining the re sul ts of BDS
and SHS for comparison. L ike for the α 4 - relax ati on, the t emp erature d ep en dence o f the r elax at io n
rates of the α 1 - relaxation is curved when plotted ver s us 1/T and has to be described by a
VFT - equ ati on. T he esti mat ed VFT par amet ers a re sum mari zed in T able S 3. T g th erm al found to be
242 K for LC536 and 248 K f or LC537 are i n go od agreem ent wit h th e temp eratu re wh er e the
rela x ation time of the α 1 - relax ati on i s 10 0 s. The temp eratur e dep end enc e of th e relax at ion rates
of the α 1 - process has a cl ose res emb lanc e wi th t hat o f PE which is included in Fi gur e 44. For that
reason, the α 1 - process det ected in the Cry 1 phase is attributed to the coope rative fluctuations of

96

alk y l chains. A similar PE - like gla s s y d yna mi cs have been found for pyrene - based D LC 33 and
polymers having l ong alkyl groups in the side chain 22 .

180 200 220 240 260 280 300
1.4
1.6
1.8
2.0
180 200 220 240 260 280 300
40
60
80
100
120
140
160
T [K]
5.6 x 10
-2
Hz
T
dynamic
g
c
p
' [J g
-1
K
-1
]
T [K]
160 Hz
80 Hz
U
R
[µV]
40 Hz
20 Hz
T
dynamic
g

Figure 46 . (a) T emperatu re d ependence of th e real par t of th e co mplex diff ere ntial voltage U

R
for LC536 for t he
heating r un at different frequencies as in d icated. (b) T emperatu r e dependence of the 𝑐𝑐

𝑝𝑝
′

for LC536 at 5.6 x 10 -2
Hz .
Solid vertic al

lines i ndicate th e m id - step p ositions.
Howeve r, t he t emper atu r e depend en ce o f the r el ax at ion rates of th e α 4 - proce ss es probed b y
BDS is c ompletely different from th at of the α 1 - p ro cesses as wel l as from t hat of t he α - pro cess o f
PE . Therefore, the molecular or i gin of the α 4 - re lax ation should be diffe rent from that for the
α 1 - re laxation. Diff e rent possibilities for a molecula r assig nment of the α 4 - relax atio n c an be
discussed. Firstly , i n the chemical struc t ure of LC536 and LC537 , the alk yl arms ar e attach ed to
the phen y l rin g which is also linked to an ester group (see Fi gu r e 18 ). The ester groups might be
(b)

(a)

97

involved in the fluctuation of the alk y l arms but on a shorter length sca le. 33 Therefore, the
α 4 -re l axation might be rel ated to cooperative fluctuations of the ester group together wit h parts of
the alk y l groups. It is important to underline again that BDS senses dipole fluctuations and SHS
senses entropy fluctuations. The densely packed c r ystals in the Cry 1 phas e e x ert higher res tri ctio ns
on the ester groups than the alk y l arms. This woul d explain wh y the temperature dependence of
the rel ax atio n rates of th e α 4 - proces s es is much stronger in the sense of the fragility concept of
gla ss formation 15 2F
153 (closer to an Arrhenius- depe nd en ce) than that of α 1 - proces ses .
Secondly, one also has to consider that the triflat e counteranions carry also a considerable
dipole moment. To ensu re el ect rical neut r alit y the t rifl ate cou nte rani ons m ust be l ocated cl ose t o
the guanidinium group al so in the plastic cry stal p hase. I n thi s second approach, the α 4 - pro ces ses
might be also assigned to coopera ti ve fluctuation s of the triflate counteranions together with the
gua ni dinium groups. Due to the plastic crystalline structure, these fluct uations will be highl y
restricted which will also explain the observed relatively strong behavio r of the α 4 - proces ses. Til l
now it could be not discriminated betwe en both interpretation possibilities. This would require
additional investigations. Nevertheless, in the light of the results presented in ref. 153F 154, the second
interp retation se ems to be more like l y .
Finally , i t should be recalled that the α 4 - relax ati on i s quite broad. The re a son for this broad
peak mig ht be that the re is an underl y in g second relaxation process corresponding to the
α 1 - proc ess. But the intensit y of the second process is qui te low due to the low dipole moment.
Theref o re, it could be not anal y z ed unambiguousl y.

98

4.3.3. Conduct ivity
In addition to the relaxation processes , also a conductivit y contributi on is obs erved a nd
anal y z ed for both ionic liquid cr y st als. Both the arom atic moieties (due to π−π sta cking) and trif late
anions may distinctivel y contribute to the conductivity . Therefore, the conductivit y mechanism
should be revea led. Th e relationship between the complex dielectric function 𝜀𝜀 ∗ and the complex
conductivity 𝜎𝜎 ∗ is given in eqn.s (20) , (21 ) and (22 ).

Figure 47 .

Frequency dep endence of the real part o f the complex conductivity 𝜎𝜎 ′

at the in di cated temperatures for the
second heating run; (a)

LC536 and ( b) LC537
. Dashed lin es indicate the plateau correspo nding to the DC
co nduc ti vit y.

The frequenc y dep endence of the 𝜎𝜎 ′ , given in F i gu re 47, shows the t ypical behavior of
semiconducting disordered materials such as ionic glasses, ion conducting p olymers, and electron-
conducting conjugated pol y m ers, which is shown in F i gu r e 10 . The fre quency dependence of
𝜎𝜎 ′ ( 𝑓𝑓 ) can be approx i mat ed b y Jo n s cher - equation given by eqn. (23). By fitting the
Jonscher- equation the DC conductivity is es ti mat ed , and i ts temp eratu re d ependen ce i s given in
Fi gu r e 48 . Conduc t ivit y c ontributions were observed in the Col h p hase as well as i n t he C r y phas e.
The ph as e trans it ion s we re als o reco gni zed as ch a nges in t he t emp eratu r e d ependen ce o f the 𝜎𝜎 𝐷𝐷𝐶𝐶 .
(a)

(b)

99

The th ermo d ynamical l y met ast able C r y 1 - Cr y 2 transition appear i ng only upon heating is also not
refle cted duri n g cooli n g in the t emperat ur e dep end en ce of t h e DC conductivit y.

Figure 48 . DC co nduc tivi t y σ

DC
for ( a) LC536 and ( b) LC53 7 in dependence of the inverse temperature. The solid
and dashed black l i nes are the fits of

VFT - eq uation (e q n. (2)) and Ar rhe nius - equation (eq n. (1 )) to
the data
respectively .

The dashed - dotted li nes poi nt out the pha se tran sition te mperature s for the hea ting c ycle as indicate d.
In th e plas tic cr y st all in e phas es, t he val u es of t he 𝜎𝜎 𝐷𝐷𝐶𝐶 are quite low. W ith increasing
tempe rature, at the phase tr ansition fro m the cr y stalline Cry 2 ph as e the 𝜎𝜎 𝐷𝐷𝐶𝐶 chan g es b y
approximately 4 orders of magnitude to values w hich are t y pi cal for semiconductors (10 - 8 - 10 -5
S cm -1 ). This indi cates a c han ge in the underly i ng conduction mechanism. R ecently , Floudas et
al. 1 54 have investig ated the ionic conduction in hex a - peri -hexabenzocoronenes- based liquid
crystals doped with LiOTf. This s y st em can be c onsidered as a rel ated s ystem co mpared t o t he
IL C s considered her e because a similar phase behavior is observed. Furthermore, a similar ionic
moiety, L i OTf, is used as doping agent, and similar value s of the DC conductivit y are reported.
Theref o re, it is con cluded that in the Col h phase the main conduction mechanism is due to ionic
mobilit y rather than due to the e l ectrons of the π - π s tacked arom ati c co res . In a further stud y , i oni c
condu ctivities of imida z olium - b ased ILCs havi n g vari ous alk yl chain l en gth s were i nves t i gated . 1 5 4F
155
The ionic conductivit y v alues in Col h and Iso pha ses were also reported in the range of 10 - 2 - 10 -7
(a)

(b)

100

S cm -1 for those IL Cs. Th is further supports the assignment of OTf ions as the main active charge
carri er in t he Co l h phase. As illustra ted in Fi gur e 18b, the tri flat e count era nio ns are l ocated i n the
center of the columns for ming the Col h pha se. Theref or e, it is assumed that the conduc ti vit y i n the
columnar phase is due to a lon g - range diffusion of the triflate anions inside the columns (ion
channels). In the Cr y phase , the i on channels do not exist. Furthermore, t he ionic mobilit y is
rest ri cted b y t he cl ose - packed crystals. Therefore , it is concluded that the na ture of the conduction
process is due to the elec t rons of the π - π stacked aromatic cores. This assumption is further
supported by t he similar conductivit y values found for the Cry phase for a non -ionic
triphe n y len e - based D LC (~1 0 - 13 S cm -1 ), in which the conduction is due t o electrons of the π - π
stack ed a romat ic cor es . 1 48
On the one hand, in the colum nar phase , t he t emp eratu r e dep enden ce o f t he DC cond u ctiv it y
is curved when plotted v ersus 1/T and has t o be described b y the VFT - equ atio n (eqn. (2)) . The
esti mat ed param ete rs are given in Appendix IV i n T able S 3 . This temperature depe nd ence of the
DC cond uctivity mig ht be relate d to the glassy dyna mics in the plastic crystalline phase obse rved
by dielectric spe ct roscopy. On the other hand, in the Cry 1 phase, i t follows t he Arrhe nius -equation
(eqn. (1)) . Activation energies of 89 kJ mol -1 for LC536 and 83 kJ mol -1 for LC537 were est im ated.
4.3.4. Conclusion
The mole cular mobility i n two linea r - shape d tetramethy lated guanidiniu m triflate IL Cs h aving
diffe rent length s o f alk y l ch ains w as ex plored by BDS and SHS. Two rela x ation processes were
detect ed in t he C r y phase b y B DS for both ILCs. The γ - p rocess es at lo wer tem p eratur es are
assigne d t o localized fluctuations of methyl gr ou ps including nitrogen a t oms in the guanidinium
head . Th e α 4 -p roc esses a t th e higher t emperat u re havi ng a VFT - l ike t emp erat ur e depen den ce of
the relaxation rates are attributed to cooperative fluctuations. I n addition to the α 4 - process es

101

detect ed b y BDS, an α 1 - proce ss i s observed by SHS for both IL Cs whi ch has also a VFT - like
temp eratur e dep en denc e of t he relax ati on r ates. Th e t emp erat ure depen d enc e of th e r el ax ati on rat es
o f th e α 1 - rela x ation is comple tel y dif ferent than that of the α 4 - rela x ation. Thus, it i s conc luded that
the mole cular or igins of the glassy dy namic s detected b y BDS and SHS are different. On the one
hand, t he dipole fluctuations of α 4 - processes sens ed b y BDS are eit her as si gn ed to the co operat ive
fluctu ations taking place in the aro matic core or in the vicin it y o f the aromatic cor e of the ILC
mol ecul es or to coop erative fluctuations of the triflate counteranions together with the guanidinium
groups. On the other hand, the molecular mobilit y of α 1 - proces s es sen s ed b y SHS wh ich i s
sensitive to entropy fluctuations is a ssigned to the alky l arms due to their quite similar te mperatur e
depend en ce of th e relax at io n rat es of th e α 1 - re la xation to that of dielectr ic α - r elax at io n of PE .
Moreover, the condu ctivit y of both IL C s was also investigated by BDS. The temperature
dependence of the DC conductivit y obse rved in the Col h m esophase has to be de s cribed b y
VFT - equation which indi cates cooperative pr o cesses. However, in the Cry p h ase , t he DC
conductivity follows the Arrhe ni us - equation. These different dependencies of the DC conductivity
in the differe nt phases indicates a change in the conductivity m echanism from ionic conduction in
the Col h mesophase to a mechanism which is d ue to the delocaliz ed electrons of the stacked
aroma tic s yste ms.

102

CHAPTER 5 – A COLUMN AR DI SCOTIC LIQUI D CR YSTAL
UNDER NAN OS CALE C ONFINE MENT
This chapter is reproduced/adapted from A. Yildirim , K. Sentker, G. J. S males, B . R. P auw, P.
Huber, A. Schönhals, Col lective orientational order and phase behavior of a discotic liquid cr ys tal
under nanoscale c on fine ment, Nanoscale Adv. 2019, 1, 1104 –1116., with permissio n from the
Roya l Societ y of Chemistry ( DO I: htt ps://doi.org/10.1039/C8NA00308D ).
T he phase behavior and molecular ordering of t rip hen y len e - bas ed D LC HAT 6 (see
Fi gu r e 15 a) under c ylindrical nanoconfinement are studied utiliz ing DSC and BDS , wh ere
cy l indrical nanoconfinem ent is established through embedding H AT6 int o the nanopores of AAO,
and a silica membra ne wi th pore diameters ra n ging from 161 nm down to 12 nm. Both unmodified
and modified pore w alls were c onsi dered . I n the l att er case , t he po re wal ls of AAO m emb ranes
were ch em ical ly treated with the surfac e modifiers OPA and ODP A . P hase transition enthalpies
decrease with decreasing pore size, indicating t hat a large proportion of the HAT 6 molecules
within the pores has a dis ordered structure, which incre as es with decreasing pore size for both pore
wall s. In the c ases of the OP A - and ODPA - modifications the amount of ord ered HAT6 is i ncr eased
compared to the unmodifie d case. The pore size dependencie s of the phase tra nsi tion temperatures
were approximated using the Gibbs-Thomson- equ atio n, wh ere th e est im ated s urf ace t ens ion is
dependent on the molecular ordering of HAT6 molecules within the pores and upon their surface.
B DS wa s emplo y ed to investig ate the molecular o rdering of HAT6 wit hin t he nanopores. These
investigations revealed that with a pore size of a round 38 nm, for the samples with the unmodified
pore walls, the molecular ordering chan ges from planar axial to hom eotro pic radi al . Ho wev er, th e
planar axial configuration, which is suitable for electronic applications, can be successfull y
preserved through OPA- and ODPA -modifications for most of the pore sizes.

103

5 .1. Mesomorphic Properties of Bulk
The mesomorphic prope rtie s of HAT 6 in the b ulk state w ere studied by DSC and POM. DSC
thermograms of HAT6 are given for the second heating and the cooling runs in Fi gur e 49. T h e
phase transition temperatures and enthalpies are estimated from the max imum positions of the
peaks an d th e area und er t he peak s resp ect iv el y and given in Table 7 . M oreover, the C ol h - I so phase
trans ition tempera tures were a lso determined by B DS f rom the first derivative of ε′ with r espect to
temp eratur e. A h yst eres is between t he coo li n g and h eat in g c ycles was obs erved whe re t h e
hysteresis is more pronounced for Cr y -Col h transition (ΔT = 15.9 K) t han Col h - Is o tr ansition
(ΔT = 2.8 K).

Figure 49 . DS C the r mo gr a ms o f HAT6 d urin g heati ng (r ed line) a nd co olin g (blue l ine) with a heati ng/co olin g rate
of 10 K min

-1
. Da she d li nes p o int o ut the p ha se tr an sit io n te mper at ur e s up o n heat i ng a nd co o ling. T he i ns et e nlar ges
the tem per ature range between 170 K and 270 K for the h ea tin g ru n.

Table 7. P hase trans i tion temperatures and enthalpies d etermined together with the literature v al ues
Source Run
Transitio n s Tempe rat ures a nd Entha lpies

DSC

BDS

In thi s st ud y
Cool ing

Cry 325.9 K (52.5 J g -1 ) Co l

h
369.3 K (6.8 J g -1 ) Is o

Col

h
369.6 K Iso

Heating

Cry 341.8 K (51.3 J g -1 ) Co l

h
372.1 K (6.8 J g -1 ) Is o

Col

h
370.3 K Iso

Ref. 40

Heating

Cry 340.6 K (50. 6 J g -1 ) Co l

h
371.5 K (5.9 J g -1 ) Is o

-

Ref. 77

Heating

Cry 342.7 K Col

h
372 .7 K Is o

-

Ref. 21

Heating

Cry 342.0 (49.9 J g -1 ) K Col

h
372.3 K (6 .8 J g -1 ) Iso

-

Ref. 51

Heating

Cry 342.0 (49. 9 J g -1 ) K Co l

h
372.3 K (6.8 J g -1 ) Is o

-

104

A step in dicating a thermal glass tra nsit ion was observed in the temperature ra n ge between
170 K and 270 K, see i nset of Fi gu r e 49 . The mid - step position of the step was taken to de t ermine
the T g t h erma l of 214 K. The Δc p was found to b e 0.25 J K -1 g -1 . Undergoing a glass transition impl ies
that there a re s ome d iso rd ered o r amorphous structures within the material. Such disorder, which
lead s to a glass transition may be caused b y a nanophase s eparation of the alky l ch ain and the
aromat ic cor e of HAT6 , is evidence d b y th e amorphous halo observed in the X - ra y pattern o f
HAT6 . 21 Similarly , Yildirim et al. 4 0 reported a glass t ransition for HAT6 al so d etect ed b y DSC.
In c ontr ar y t o our findings, they f ound a T g th er ma l at 186 K. Furthermor e, Kr ause et al. 21 observed a
step, which might indicate a glass transition, in the tempera t ure range of 180 K - 220 K upon
cooling. The y did not observe a glass transi tion during the heating run. Cla rif y ing these
contradicting finding s requires further detailed cal orimetric investiga ti ons, such as conventional
DSC investigations covering temperature s l ower than 150 K or Hyper / Flash DSC investig ations
allowin g for hig h er he at ing r ates .

Figure 50 . POM imag e s of H AT6 , recor ded under crossed po larizers, in the li q uid cr ystallin e cell having ITO - coated
electrodes (a) at 32 8 K in the Cry p hase during the

first hea tin g r un fro m ro o m te mpe ra t ur e ( b) at 363 K in the Co l
h
pha se d ur i ng t he fir st hea ti n g run ( c) at 36 3 K i n t he Co l

h
p h ase dur in g t he t hird he at i ng r u n. T he inset s o f ( b) and ( c)
are the drawings represen ti ng the m olec ular ordering for a given image. Scale bars represen t 20 0 µm.

Fi gu r e 50 illustrates the tex ture and the column alignment of bulk HAT6 obtained by POM .
Upon first heating from room temperature, in the Cr y phas e at 328 K the texture is very bright
under cross polari zers. This indica tes a lack of a homeotropic ali gnme nt d ue to tilte d columns in
the Cry pha s e (herringbone- like cry stal packing 37 , 154 ) causing a high bire f ringence. This re s ults in
(b)

(a)

(c)

105

a bright texture with colored cry s tal domains. 48 A f an - shap ed t ex tu re acco m pani ed b y dark are as
was observe d durin g the first heating ramp in the Col h phase at 363 K. Th e fans - shap e tex t ure i s
t y p ical for a C ol h phase of DL Cs. It indic ates that a column alig nment in large spa tial regions is
not present. As it is shown in the inset of Figur e 50.b the columns are randomly tilted. 13 ,
155F
156 In
addition to the fans, the small dark areas were also obs erved, which indicate that the columns are
partia ll y ali gne d homeotropica ll y among th e tilted columns causing a minimal bire fring en ce.
However, during the thir d heating run (after appl y ing two heating/cooling cy cl es in the range from
350 K to 383 K) at 363 K, large da rk areas are observed (see F i gu r e 50.c), wher e the columns are
mostl y ali gned homeotropicall y . The reason of th e hom eotropic alignment of the columns in large
spatial regions compared to the first heating, probably is the temperature program applied due to
the s elf - healing ability of DLCs for the structural def ects with therma l anneali ng. It could also be
reasone d that the heating/cooling rate applied, 1 K min -1 , i s not slow enough to ali gn the columns
during the first heating due to what is assumed to be slow orientation kinetics.
5 .2. Phase Be havior Under Na nos cale Confinement
Fi gu r e 51 a and b depict the DSC thermo grams of bulk HAT 6 as w ell as H AT6 confined into
the nanopores of unmodified, OPA - and ODP A - modified A AO mem br an es. It is concl ud ed th at
the confined HAT6 unde rgoes both phase transitions (Cry -Col h and Col h - I s o ) wit h decr eas in g pore
size for both unmodified and modified pore walls. One exception to this is observe d with H AT6
confined within 12 nm pores in a silicon membra ne, wh ere the Col h - Iso phase t ransition is
completely suppress ed. Such a complete suppression of the phase tr ansition has previousl y be en
reported fo r ro d - like L Cs . 136

106

Figure 51 . DSC t her mo gr a ms o f bul k HA T6 a nd HAT6 conf ined in to (a) unm odi fi ed (b) OPA - modif ied and (c )
ODPA

-
m od ified nanopores of the me mbranes having different pore sizes as indicated (the second heating cycle). The
dashed lines indicate the phase transitions te m p eratures of bu lk

HA T6 . (d) DSC t he r mogr a ms o f HA T6
co nfi ned i nto
unmodified nan o pores of the m e mbranes having d ifferent pore sizes as i ndicated, enlarg in g th e te mperature range
from 320 K to 35 0 K for th e heat flows of the sam ples given in

Fi gur e 51 a. The dotted lin e i ndicates the Cry - Col
h
phase transit io ns temperature of th e b ulk.

As previously reported for the phase behavior of HAT 6 under confinement for a limi ted range
of pore sizes, 51 three c o nclusions can be drawn for both kinds of sample s with unmodified and
modified pore w alls. F irs tly, b oth phase transitio n temperatu r es shift to lo wer tempera tures with
decreasing pore size. Secondl y , bot h phase transition peaks split i nto two or three for por e sizes
smaller than 95 nm (see F i gu r e 51 d). The appearance of so - ca lled satellite peaks in a ddition to the
main transition peak for t he smaller pore sizes was repor ted for nanoconfined pyrene - based D LC
and also for HAT6 . 51 , 52 In th e first inter pretation , the s atell it e peaks can be due t o rem aini n g
(a)

(b)

(c)

(d)

107

bulk-l ike HAT6 located at t he su rfac e of t he s am pl e alt hou gh i t was t ried t o remo ve it car efu ll y .
A similar interpre tation is used elsew h ere. 156F
157 Secondly, the m ain and the satellit e peaks might be
assigne d t o different configurations of the molec ul es near the pore w alls and the pore cente r. This
conclusion is supported by t he observation that the satellite peaks ar e shifted to lower temperatur es
w ith respect to the phase transition of the bulk and depend sl ightl y on po re siz e. For the s e reasons
the second interpr etation is favored. However, such assignments are contro versial due to the lack
of ex peri ment al t echni q ues av ailab le t o char act eriz e th e d ifferent structures and their location
within the pore space . Thirdl y, f or both phase transit ion s, the enth alpi es decreas e with decreas in g
pore size. Howeve r, thi s conclusion cannot be drawn directl y from Fi gur e 51 , as th e measu red
values are normaliz ed to the c onfined mass of HAT6 . This third conclusion is discussed in detail
below.
The depende n ce of phase transition enthalpies normalized to sample mass inside the pores and
the phase tra ns ition tem peratures are shown in Fi gu re 52. Mo reov er, t he effe ct of t he di ff eren t
host/guest interactions on the phase be havio r under nanoconfinement is revealed b y comparin g the
behavior of HAT6 confi ned in both unmodified and modified po res. The OPA and ODPA
modific ation s form a stable grafted alk y l chain monola y e r, which results in hydrophobic pore walls
with a lower value of the surface energ y c ompa red to unmodi fied pores. 157F
158 ,
158F
159 The thickness of
ODPA - coating was repor ted to be 1.8 -2.4 nm on alum inum oxide surface, 159 F
160 whic h i s comparable
to the thickness revea led from SAXS investigations. Hence, the modific ation l eads to an observe d
decrease of t he pore diame t er of ca . 4.4 nm for the ODPA - modified AAO membrane s. The
infl uence o f the d ecrea s ed pore size should be g r eater for smaller pores than for la rger ones
considering inverse pore siz es. Fi gu r e 52 shows t he dependencies for th e nominal pore sizes.
However , the dependencies given in Appe ndi x V in Fi gu re S 35 for the sample with the

108

ODPA -modified p ore su rf aces w ere dr awn co nsi d ering a 4.4 nm d ecreas ed por e siz e. I t should be
noted that the thickness of the ODPA - coating is not known for the pores fill ed with HAT6 . W hen
the modified pores are filled with H AT6 , the thickness of the co ating can, in principle, have a
value between 0 nm - 4.4 nm , whereas in reality values tend to lie towards the latter end of this
scale.
The dependenc i e s of the phase transition enthalpies of the main pe ak ( normalized to the mass
o f the con fined m ateri al ) on pore s iz e ar e giv en in Fi gu r e 52 a and c for the C ry -Col h and the Col h -
Iso tra nsit ions respectivel y. The normaliz ed phase transition enthalpies decre ase with decreasing
pore size, which provides evidence that a portion of confined HAT6 do es not undergo the phase
transition. This part of the confined HAT6 s hould be disordered a nd ma y hav e an amorphous
structure. As discussed in r ef. s 51 and 52 , the observed increase in surface cur vatur e, with
decreasing pore size, leads to stronger elastic distortion of the ord ered phase, which prevents the
molecules from for m ing an ordere d st ructure a n d consequently limits the amount of obse rved
ordered ph ase.
The dependencies of the enthalpies for the Col h - I s o transition reveal that m ore than half of the
material conf i ned in the pore (by volume ) is disordered for por e sizes smaller than 47 nm. This is
an amount that cannot b e neglected in t he interpretation of the results for nanoconfined HAT6 .
The sp ati al location of this disordere d portion i nside the por e cannot be assigne d b y methods
chara cteri zi ng th e st ructu r e such as XRD o r n eutr on scatt erin g. As it has b een d iscu ssed th at t he
disordered por t ion is likel y t o be locat ed at th e cen ter of t he po re du e to div ergenc e of t he ex cess
ener gies towar d the p o re c ent er. 31 , 72 , 75 A di sord er ed co r e at the cent e r o f the p o re w as also
visualized b y molecular d y namics simula tions of confined H AT6 . 54

109

0.00 0.02 0.04 0.06 0.08 0.10
10
20
30
40
50
0.00 0.02 0.04 0.06 0.08 0.10
325
330
335
340
345
1/d
[
nm
-1
]
Bulk HAT6
Unmodified
ODPA modified
OPA modified
∆Η
Cry-Colh

[J/g]
pSi5
σ
OPA
= 5.3 mN/m
pSi5
T
Cry-Colh

[K]
1/d
[
nm
-1 ]
σ
ODPA
= 5.1 mN/m
σ
Unmod
= 5.4 mN/m

0.00 0.02 0.04 0.06 0.08 0.10
0
1
2
3
4
5
6
7
8
0.00 0.02 0.04 0.06 0.08 0.10
350
355
360
365
370
375
Bulk HAT6
Unmodified
ODPA modified
OPA modified
1/d [ nm
-1
]
pSi5
∆Η
Colh-Iso
[J/g]
σ
OPA
= 0.9 mN/m
σ
Unmod,2
= 0.8 mN/m
σ
Unmod,1
= 2.2 mN/m
T
Colh-Iso
[K]
1/d [ nm
-1 ]
σ
ODPA
= 0.9 mN/m

Figure 52 . Dependencies of the phas e transition enthalpies for (a) th e Cry - Col

h
tra nsit i on a nd (c ) the Co l

h
- Iso
transi tion, as well as the dependen cie s of the phase transit io n temperatures for (b) the Cry

- Col h
tra nsiti on a nd (d ) the
Col

h - Iso transiti o n versus inverse pore size. Blu es squares indicate data for bulk HAT6 , black sym bols
indicate data
for

HAT6 c onfin ed i nt o unmodif ied mem branes, g reen sym b ols in dicate data for HAT6 c o nfi ned i nto OP A -
modified
mem branes, a nd red sy mbols i ndic ate data f or

HAT6 confined i nt o ODPA -
modified membranes (filled circles: main
peak , open sym bols: sa

tellite peak). Dashed - dotted li nes are guide for e yes. Solid li nes are the fits of eq n. ( 32 )
to the
dependencies. Note th at for the samples with modified pore surfaces, th e p ore dia met er was corrected r egarding the
estimated th ic kness of the surface layer.

The po re siz e dependenci es of the phase t ransition enthalpies show stron ger dependence on
pore size for larger pores in comparison to smaller ones. Simi lar findings w e re reported for a series
of organic materials confined within nanopores. 16 0F
161 T he surface area of the por es per unit of mass
is significantly higher for smaller pores. This ca n lead to stronger confinement effects on the
entha lpies for smaller p ores f o r nanoconf ined materials , which could explain similar trends
observed with different nanoconfine d m aterials. In addition, higher values of the transition
enthalpies wer e found for surface modified samples compared to unmodified one s. Thi s means
that the amount of order ed HAT 6 in creases fo r t he s ampl es wi th t he OPA - and ODP A -modified
(a)

(b)

(c)

(d)

110

pore walls even though there is still a considerable amount of disordere d m aterial inside the pores,
most likel y located in the pore center.
Fi gu r e 52 b and d show t he dependencies of the phase transition temperatures on inverse pore
size for both phase transit ions. It can be seen that t he phase transition temperatures decrease with
decre asin g por e siz e. In general , the pore size dependence of pha s e transition tem perat ures c an be
well descri bed b y t h e Gib bs -Thomson- equation for a varie t y o f materials including LC s . 51 , 52 , 162 , 163
The Gibbs-Thomson- equat ion read s
∆𝑅𝑅 = 𝑅𝑅 𝑚𝑚 , 𝑏𝑏𝐹𝐹𝑏𝑏𝑏𝑏 − 𝑅𝑅 𝑚𝑚 ( 𝑑𝑑 ) = 𝑅𝑅 𝑚𝑚 , 𝑏𝑏 𝐹𝐹𝑏𝑏𝑏𝑏 4 𝜎𝜎
∆𝜕𝜕 𝑚𝑚 , 𝑏𝑏𝐹𝐹𝑏𝑏𝑏𝑏 𝜌𝜌 𝐻𝐻𝐴𝐴 𝑇𝑇 6 𝑑𝑑

(32)
where T m,bul k is t he phase transition temperature of the bulk material, d is the pore diameter, T m (d)
is the pha se transitio n temperatu re of HAT6 within the pores of diameter, d, and σ is the s urface
tension of the interface. ΔH m, bulk is th e phase tr an sition entha lp y of the bulk mate rial.
For the pha s e transition from the Cr y to Co l h phase, the data seems to follo w the
Gibbs-Thomson- equation for bo th pro bed t ypes o f s ampl es. T he su rfa ce t en sio ns were cal culat ed
to be 5.4 mN m -1 , 5.3 mN m -1 and 5.1 mN m - 1 from the dep end enci es o f C ry -Col h phase transition
temp eratur es for the samples with unmodified , OPA - and ODPA - modified pore walls,
respect ivel y . T he OPA and ODPA modif i cation s make the por e wall more h y d rophobic in
comparison to the unmodified pore w alls. Therefore, the interfacial tension is lower for sa m ples
with modified pore walls than for unmodified o nes. Fi gu r e 52d depi cts that the dependence of
phase transition temperatures of the Col h - Iso p has e tran sit io n ch an ges at a pore s iz e of ca. 38 n m
for the samples with the unmodified pore wal ls. Assuming that both pore size dependencies can
be described b y a Gibbs -Thomson- equation for pore sizes larger than 38 nm, t he surface tension
was c alcul ated as 2.2 m N m -1 , whilst f or pore sizes smalle r than 38 nm a val ue of 0.8 mN m -1 was

111

calc ulated. As it w ill be discusse d below in more de tail , this change in the pore size depende nc e
of the phase tra nsit ion temperature f o r the Col h - I s o phase transition goes along with a c han ge in
the dominating order. It is also important to note that the pore si ze dependence of the Col h - Iso
phase transition observed here is different from that reported in ref . 73 . The reason for this is not
quite clear and re qui res addit ional experiments.
The pore size dependency of the phase transition temperature of the Col h - Iso phase transition
for th e s amples w ith the OP A and O DPA mo dif ied p ore wall s can be d es cribed wi th a sin gle
Gibbs-Thomson- equation where a value of 0. 9 mN m -1 was calculated for the surface tension. This
value is quite similar to the one obtained for the unmodified pore walls for smaller pore sizes. I t
migh t be concluded that the t y pe of dominatin g anchoring is the same in both cases. Moreover, a
study on the effect of orientation on the reduc t ion of the phase transition t emperature revealed b y
SHS for a confined rod - like liqu id cr y stal 161F
162 demonstrated the stronger decr e ase of t h e trans it ion
temp eratur es for a rad ial confi gur ati on. In a dd iti on, the favora bl e inte ractions between the
aromat ic co re and t he po l ar su rfac e of th e un modi fied mem bran es en fo rce l ik el y fac e - on anchorin g
lead ing to homeotropic radial configuration (logpile) . H ence, it can be concluded that the
homeotropic radia l configuration is the dominant ty p e of ordering found in larg er unmodified
pores . Recen tl y , Zhan g et al. 77 found also dominant log pi le configuration for HAT6 confined in
native nanopore s o f AAO membranes.
For the smaller unmodified pores and for the m odified pores, it was assumed that the
dominating ty p e of orderi ng is a plana r ax ial configuration. The similar values obtained for t he
surface tensions ( 𝜎𝜎 𝑈𝑈𝐹𝐹𝑚𝑚𝑈𝑈𝑑𝑑 , 2 ≈ 𝜎𝜎 𝑂𝑂 𝐷𝐷 𝑃𝑃𝐴𝐴 = 𝜎𝜎 𝑂𝑂𝑃𝑃𝐴𝐴 , Fi gu r e 52d) further suppor t this assumption. The
plana r configuratio n is assume d for sample s with the modified pore walls d ue to the similarity
between the al k y l ch ains and t he alk yl chains graft ed t o th e surface o f the m odi fied mem branes .

112

On the contrar y , findings in the literature for confi ned HAT6 point out l ogpile configurations in
unmodified small pores 77 and circ ula r concentric (planar radial) configurations in nanopores
grafted b y alk y l ch ains . 76 Alt hough the calorimetric investigations give a clear picture of the phase
behavior under confinement, t h e y reflect some understanding about the do minating configuration
in the nanopores ba s ed on the pore size depe ndencies of the phase transitions tempera tures and
enthalpies. Thes e predictions will be ree valua ted with respect to th e orientational order
chara cteri zed b y BDS in the next section.
5 .3. Orien tat ional O rder under N anosc ale C onfine me nt
The collective o rienta tio nal orde r o f HAT6 in the bulk and confined HAT6 was reve aled b y
BDS . Of course, BDS is not a tool to e stimate the struc ture directly. BDS is sensitive to dipo le
orientation (dipole vec t or with respect to the out er electr i cal fi eld). Ther efore, a ch an ge in th e
orientation at the phase t r ansition can be monitored when a change of the orientation of the dipole
moment is involved. Together with a reference measureme nt on the bul k material w h ere t he
orientation is known conclusion based on facts about the orientation can b e drawn . The
measu rement s w ere carried out at a fre qu enc y of 3 5 kHz, where results from the third heating r u n
are provided in Fi gur e 53 . A frequenc y o f 35 kHz was selected for these investigations as n o
diel ectri c act ive p rocess e s due t o mo lecul ar flu ctuat ion s for H AT6 t ake pl ace in t he tem perat u re
range from 350 K to 38 3 K. In this temperature range , t he relax at io n pr ocess es t ak e pla ce at
frequen ci es bet w een 1.9 MHz to 1.2 GHz (obtained from the e x trapolation of the data g i ven in
ref. 40 ). Hen ce, a me asu rement f requen c y of 35 kH z i s si gnifi cantl y l ow er th an th e f req uen c y
window of the dielectri c relaxation processes, and the measurements shown in F i gu re 53
corre s pond to quasi - stat i c diel ectri c me asu rement s where onl y t he col lect iv e ori entat io n of H AT6
contributes to 𝜀𝜀′ , which can be c onsi dered as frequency-independent.

113

Figure 53 . Normalized dielec tric pe rmitivities as a functio n of te mper at ure dur in g the thir d hea ting r u n for the bul k,
sam ples w ith unm odified, OPA

- a nd ODP A -
modified pore walls as indicated. All measurements were done with a
heat i ng/co o li ng r at e o f 1

K mi n -1 at a frequency of 35 kHz. T he dashed - dotted lines indic ate t he Col h - Iso
phase
transi tion temperatures determined b y DSC. The dashed lines represent t e mperature dependencies of

𝜀𝜀′
extrapolated
fr o m

Col h and Iso phase s. T he inse t s on t he ri ght - top are t he drawi ngs il
l ustr at in g the mea s ure me nt geo m e tr y used fo r
the d

ielectric measure ment for b ulk HAT6 i n the cell and the conf i ned HAT6 .

114

I n the B DS measu rements, the cy lindrical pore s were oriented pa rallel to the e lectric f ield
appl ied d ue to t he par allel pl ate geomet r y (see t he in set o f Fi gu re 53 ). Th erefo re, the s ystem c an
be considered as AAO and HAT6 cap aci tor s connect ed i n p arall el y i eld ing to an addi ti ve
response. 136 Thus, the absolute value of the per m ittivit y of such a s y st em is related to the porosity
of the membrane. For this reason, the measured 𝜀𝜀′ val ues were nor malized with respe ct to the
values of 𝜀𝜀′ at 383 K for each sample.
The e x cess pe rmittivity ( Δε ) can be de fin ed a s th e diff eren ce b etwe e n th e temp eratur e
depend en ce of 𝜀𝜀′ in the Col h phase, and that of 𝜀𝜀′ extrapolated to the Col h phase f rom the
dependence in the Iso pha se . A positive Δε was determined for bul k H AT6 , wh ere HAT6
molecules are homeotropically aligned, which was also confirmed b y POM. The positive Δε
ind icates that th e colu mns are perp endi cu larl y al ign ed to the el ectr odes. Hence, a positive Δε can
be a ttributed to a do minating a x ial conf iguration, whilst a negative Δε corresponds to a dominating
radial conf i guration. I n some cases, from the ove rview given in Fi gur e 53, it is hard to dete ct
wheth er Δε i s pos iti ve or ne gative. The refo re, enl ar ged fi gures ar e p rep ared an d ad ded to
Appendix V (see Fi gur e S 36-S41 ).
For the unmodified pores with diameters smaller than 38 nm, the Δε w as estimated to be
positive and assigne d t o a planar axial configuration. For pore sizes greater than 38 nm, a negative
Δε obse rved and assi gned to the homeotropic radial configuration. This is in g ood agreement with
the discussion given a bove concerning the pore siz e dependency of the phase transition
temperatures. The DSC investigations indicate that a change in the anchor in g t y pe o ccu rs at a po re
diameter of ca. 38 nm, which w as also observed using B DS. Conversel y , a positive value of Δε
was found for s amples with ODPA-modified surfaces, except for the pore sizes of 73 nm and 161
nm. This has been attributed to the planar axial conf iguration , where a p l an ar radi al confi g u rat io n

115

was ass umed fo r 73 nm and 161 nm due to t h e negative value of Δε. Simila rl y , a positive value of
Δε, attributed to the plana r axial conf iguration, was found for all samples with OPA -modified
surfaces. For t he sample with a pore si ze of 47 nm with ODPA - modified pore wa l ls, generally a
positive value of Δε was found, however it was observed that the phase trans ition occurs in several
step s (see al so F i gu re S 36 ). As shown recently with hi gh re s olution optical birefringence
experiments on HAT6 confined within porous silica and molecular d ynamic simulations, 54 such
step s can b e attri but ed t o a circular co n centri c (pl an ar radial ) con fi gurat io n. Th erefo re, i t mi ght be
concluded that the orientation of HAT6 i n 47 nm m odified AAO pores als o possesses a circular
concentric (planar radial) configuration.
In addition t o the die lectric in vestigatio ns , t he mo lecul ar ord eri n g for th e s ampl es pres ented
here ( ex cep t the samples with OPA - m odi fied p ore wal ls) was als o ch a racte riz ed b y opti cal
birefri n gence (O B) meas urem ent an d tem pe ratur e -dependent XR D. Th es e meas urem ents wi ll be
reported el sew her e . 162F
163 Neverth eles s, t he resu lts of t hese m easurem en ts are incl uded here in Tabl e
8 . Some primarily ha v e been alread y publish ed discussing also the methodolog y of the
measureme nt s (see supporti ng informa t ion of ref. 54 ). Combining the results of the interpre t ations
based on the DSC investigation and the orderin g characterized by B DS, OB and XRD, a general
picture of the molec ular ordering i nside the unmodified, OPA - modified and ODPA -modified
nanopores wa s obt ained (see Table 8 ). In most cases , the results obtained from the DSC and
diel ectri c me asurem ents agree w ith the d ata obtained with OB and XRD. Th e min or di ff eren ce s
between B DS and O B fin d ings m ight b e cau s ed b y the s mal l di fferen ces i n th e s ampl e prep arat ion .
Although, it is argued in r ef. 75 that the dipolar o rientation of the polar ether groups of alk yl c hains
is sensed by B DS, whereas the orientation of the ar omatic cores is observed by OB. This may
explain the small differ ence s observed in the determined configuration by DS and OB.

116

Table 8. T he do mina ti n g or d ering o f H AT6 m olec ules ins id e the n a nopores revealed by means of different techniques
Pore size, d

( n m)
Unmodified

OPA - m odif ied

ODPA - m o difie d

DSC DS OB XRD

DSC DS DSC DS OB XRD
17

PA

PA

PA

PA

PA

PA

PA

PA

PA

PA

18

PA

PA

PA

-

PA

PA

PA

PA

PA

-

24

PA

PA + HR

HR

-

PA

PA

PA

PA

PA

-

34

PA

PA + HR

HR

-

PA

PA

PA

PA

PA

-

38

PA + HR

HR

HR

HR

PA

PA

PA

PA

PA

PA + PR

47

HR

HR

HR

-

PA

PA

PA

PA + PR

PA

-

73

HR

HR

HR

HR

PA

PA

PA

PR

PA + PR

PR

95

HR

HR

HR

HR

PA

PA

PA

PA

PA + PR

PR

161

HR

HR

HR

HR

PA

PA

PA

PR

PR

PR

PA : Planar axial, HR : Ho m e o tro pic ra dial and PR : P lanar rad ial. H AT6 co nfi ned int o t he sili co n me mbra ne
(12 nm ) i s not present ed in the table since the C o l h - Iso phase tr ansitio n is completel y supp ressed for this sa mple.
The r esults sum marized in th is tab le a re taken from r ef.s 25 and 163 .
According to the a bove discussions and Tabl e 8 , the picture of the molec ular ordering o f HAT6
inside the unmodified, OPA - modified and ODPA - m odi fied n anoch ann els o f AAO mem bran es c an
be concluded as follows: A model representin g the molecular order of H AT6 inside nanopores
should include three idealiz ed major lay e r; a disordered layer probabl y located at the center of the
pore, an a x ial ordered layer near t he center and radial ordered layers near the por e walls. For HAT6
in the unmodified nanopores, a transition of the dom inant config u ration from planar axial ( Fi gur e
3 d) to homeotropic radia l ( Fi gu r e 3 c) co nfi gurati o n was d etect ed i n t he p ore si ze r an ge from 24
nm to 38 nm. On the other hand, for H AT6 in the ODPA -modified nanopores, the transition from
plan ar ax ial ( F i gu r e 3 f) to plan ar rad ial ( F igu re 3 e) configuration was found in the p ore si ze r an ge
from 73 nm to 95 nm , wh ereas HAT 6 i n the OP A - modified nanopores show no transition and ha ve
planar config u ration.
5 .4. Conc lusion
The influence of c y lindrical nanoconfinement on t he phase behavior and molecular ordering -
two main properties determining the applications of a DLC in nanotechnology - was ex pl ored b y

117

DSC and B DS for HAT 6 confined into the n anopores of AAO and silica membranes. Pore sizes
from 161 nm down to 1 2 nm were explored. Mor eover, the different host/guest interactions and
their influence on t he phase beha vior as well as mol ecular or derin g were studied by compa ring
their behavior a nd ord ering in unmodified, OPA - and ODPA - modified pores. Prior to the
investigations, the membranes and the samples of HAT6 confined int o nanopores wer e
well - charact er iz ed b y means of vo lum etri c N 2 - sorption, scanning electr on microscop y , FT IR ,
SAXS and TGA.
The pore size depe ndenci es of the phase tra nsit ion enthalpies a nd t emperatures were obtained
b y DS C. It w as o bse rved t hat t he phas e t rans iti on en thal pi es d ecr eas e wit h dec reasi n g pore s iz e,
which ind icates th at an i ncreasi n g fract ion of H AT6 does not underg o an y phase transitions, and
it is thoug ht that this fr action is probabl y located in the center of the pore . Moreover, the phas e
trans it ion t emp eratures d ecre ase wi th d ecre asi ng p ore si ze. Thes e pore s iz e depen den cies of th e
phase transition temperatures were described b y Gibbs -Thomson- equation for both transitions. For
the C r y -Col h t ransition, a lower interfacial tension was found for the sampl es with modified pore
walls in comparison to th e samples with unmodified pore walls. The pore size dependency o f the
Col h - I so t ransition temperatures for samples with unmodified pore walls, a change from a stronger
to a weake r dep endency was observe d with a por e size of around 38 nm. S uch a change im plies
that there is an alteration i n the dominating order. Therefore, b y considering the host - gu es t
interaction it can be concluded that the dom inating t ype of ordering is a homeotropic r adial
config u ration with larger pores (d > 38 nm) and a planar axial configuration for small er po res (d
< 38 nm). Howev er, t he d epend en cies o f th e C ol h - Iso phase transition temperatures for the samples
with modified pore walls were approximated by one Gibbs - Thomson depende nc y. Similar values
for the surface tension for the samples with modified pore walls to the one was es ti mat ed for

118

samples with unmodified pore wa l ls at lower pore siz es ( σ U n mod , 2 ≈ σ ODPA = σ OPA ) was found.
Hence , i t is concluded th at for the samples with modified pore walls that the dominating t y pe of
ordering is also the planar axial config ur ation.
The collective orientational order of nanoconfine d HAT6 , corresponding to the dominating
ordering in the pore , was probed by B DS at a con stant frequency of 35 kH z. S imilar to the DSC
findings, B DS investigations revealed that for the unmodified pores a homeotr opic radi al
orientation for the lar ger pores (d > 38 nm) a nd a planar a x ial for smaller pores (d < 38 nm ) as
dominating forms of ordering. For OPA - and ODP A - modified pore walls, the planar ax ial
config u ration is assigned as the dominating ty pe ex cep t for t he ODP A - modified samples having
pore sizes of 73 nm and 161 nm. Moreover, OB and XRD studi es on the samples discussed here
mostly a gr e ed the mo lecular orde rin gs dete rmined b y B DS.
In summar y , OPA and ODPA surfac e modification s have been reve aled to be promis ing
strateg ies for controlling t he molecular ordering of D LCs inside the nanopores of metal ox ide
membranes. Our r esults indicate that the dominating planar axial config ur at ion, which is the only
config u ration suitable for el ect roni c appl ic ati ons , was suc cess full y a chi ev ed b y both OPA - and
ODPA - modifica tion s for most of the pore si zes probe d. Moreover, the highe r phas e transition
enthalpies and temperatures observed for the samples with modified pore walls compared to the
unmo dified ones implies a significant improvement in the amount of ordered HAT 6 present w ithin
the pores.

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CHAPTER 6 – C ONCLUSIO N & OUT L OO K
The aim of t he pres ented work is to ac complish a n understanding of the st ructure, pha s e
behavior, molecular dynamics and conductivit y of columnar liquid crystals (C L Cs) in the bulk
state as well as that of th e phase be h avior and collective orientational ordering of a model C L C
under nanoc onfin ement. Different CLCs forming a hexagonal columnar (C ol h ) m esop hase, were
chosen to study here (see T ab le 9). Th e s elect ed C LCs are rel ated t o hex aki s(n -
alky lox y) triphen y l ene - b ased discotic liquid cry stals (DL Cs ) ( HAT n ). HATn are cons idered as
“worki n g horse” o f the C LC rese arch s ince t he y are one of the first DL C s reported a nd t herefore
t h e y are one of th e mos t studied C L Cs as model sy stems . For this reason, hex akis[pent y lox y ]
triphe n y len e - based DLC ( HAT 5 ) and a series of dipole functionalize d
pentapentylox y t riphen ylene- based DLCs ( SHU0 9 - S HU12 ) corresponding to unfunctionaliz ed
HAT5 wer e select ed in thi s wo rk. Th e chosen dipole func t ionalized DLCs car r y different dipole
units, which are et h y l gl ycolat e ( SH U09 ), h exa noy l ( SHU10 ), trif luoromethyl ( S HU11 ), an d
diethy leneglycol ( S HU1 2 ) units. Moreov er, triphenylene crown ether - based u ns ymmetri cal D LCs
( KAL465 and KAL468 ) w ere chosen to investi gate becaus e KAL compou nds can be considered
as relat ed s ystems t o HATn with a slig htl y different c hemical structur e. Ad ditional to the selecte d
non- ionic CLCs, co lumn ar ionic liquid cr y stals ( LC536 and LC537 ) were a ls o sel ected as d if fer ent
type of columna r liquid crystalline system for the study . All above - ment ion ed C LCs wer e
investigated in the bulk state. Furthermore , a tripheny len e - based DLC ( H AT 6 ) , also having a Col h
meso phas e, was s tud ied under confin ement at n an oscal e . H AT6 i s ex ten si vel y studied model
s y s tem fo r investigation of C LCs under confinement. So far in thi s thesis, conclusions wer e drawn
for the studies on the differe nt columnar liquid cr ystalline s y stems . Th ere fo re, he re a mo re gen eral

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conclusion and a summary for the thesis as well as an outlook on the n ext i nteresting research work
are pr esent ed.
Table 9. T he studied co lumna r liquid c rystalline system s

Col umnar L iq uid
Cr ystals
(C LCs)

Type Co m po und N a me State of the system
Discotic
Li quid
Crystals
(D LC s)
Unfunctio nalized
T rip hen yle ne s
HAT6

Con fi ne me nt

HAT5

Bul k

Monofunctionalized

T rip hen yle ne s SHU0 9 - SH U12 B ulk
Cro wn ethe r - based

T rip hen yle ne s KAL465 and KAL468 B ulk
Ioni c Liqui d

Crystals
(ILCs)
Tetramethyl ated
Guanidini um T riflate IL Cs LC536 and LC537 Bul k
The work presented in the first part ( Chapt er 4 ) investig ates t h e s ele cted di fferent co lum nar
liquid cry stalline s y stem in the bulk state. The mesomorphic properties of the CLCs were studied
using polarizi ng optical microscopy (POM) and X - ra y diffr actio n (X RD) . The P OM and the XR D
investig ations reveal ed d endri meri c g rowth as w e ll as fan - shaped tex tures and p6mm s y mmetr y ,
which are ch aract e rist ic fo r a Co l h mesophase. Moreover , t he amorphous halo s observed in t he
XRD p atter n s in this study i ndi cate a nanophase separation between the f lex ible alky l substituen ts
filling the interc ol umnar area and the columns formed by the ri gid cor es. T herefo re, it might be
concluded that the nanop hase separation is a cha racteristic propert y o f C LCs. Moreover, a similar
nanophase separated morpholog y between th e flex ible n - a l k yl s ide chains and the rigid pol yme r
backbone has been evidenced for different poly m eric systems having longer n - alk yl sid e ch ains . 22
Hence , it might be further concluded that th e pre s ence of a morpholo gy of nanophase s ep arat ed
alk yl chains is ex pect ed for s y stems consistin g of rig id units an d flexible al k y l chains atta ched to
the rigid units.

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T he phase be h avior was reveal ed conducting conventional scanning calorimetry (D S C)
measu rement s . I n addition t o t he ph ase tr ans it ion temp eratu res and ent halp i es det ermi ned us ing
DSC, the DSC investigations el uci dated t h at a ll CLC s discussed here undergo at least on e thermal
gla ss transi tion. For the triphen y l ene- bas ed D LCs ( HAT5, S HU09 - SHU12, KAL465 a nd
KAL468 ), two dif f ere nt therma l glass tran sitions were found . The investigations i mpl y t hat t he
gla ss transitions r e garding t he T g,1 th erma l are associated with the nanopha se s eparation.
The mo lecul ar d y nam ics (including the g l ass y d y namics) taking pla ce in these sy stems were
studied using a combination of bro adband d iel ectri c spect ro scop y ( BDS) , speci fi c heat
spect rosco p y (SHS) and fas t scanni n g calorim etr y (FSC ) in a broad frequenc y range f rom 10 -4 Hz
to 10 9 Hz and in a broad tempera t ure range. Th e molecu lar d y n ami cs investigations revealed a
γ - process and α - processes for all C LC s studied i n this work (see Fi gu re 54). T he γ - pro cess es
detect ed b y B D S for the C LCs ar e assigned to PE - like localize d fluctuations taking place in the
alky l chains f illing the inte rcolumnar area . The α 1 - proces ses probe d b y BDS and/or by the
calori met ric techn iqu es a re unambiguousl y attributed to the PE - like cooperative fluctuations of
the al k y l ch ain s tak ing pl ace i n t he int er colu mnar area . M o reove r, other gl ass d ynamics ( α 2 -, α 3 -
and α 4 - processes) de t ected b y BDS are ambiguousl y attributed to the cooperative fluctua t ions of
the co res . For the glass y d ynamics d et ected b y bo t h BDS an d adv ance cal o rim etr ic techniques, it
is rea lized that the di ele ctri c and t he calo rimet ri c dat a a re in good agreement. The m ol ecula r
mobility investiga tions presented in this thesis , have provided an understanding of the molecul ar
dy namics of columna r liq uid cr y st al li ne s ystems i n gener al . Thu s, it migh t b e concluded for C LCs
that PE - like localized and glass d ynamics t ak e p l ace in the i nter col um nar area du e to the PE - like
structure of the m olecules of t he alk y l ch ain s of C LC s . Moreover, th e stu d y pres ented her e has
manifested the sig ni ficance of the investigation strateg y combining the BDS and the advance

122

calo rimetric techn iques to ga in insight into the glass y d ynamics fro m di ffer ent p ersp ecti ves i n a
comp lemen tar y mann er .

Figure 54 . Graphical summ ar y of the molecular d y namic s of the C LCs for the first part o f the the sis.

T he conductivit y of the CLCs w as expl ored by BDS. F or the materials unde r investigation, the
conductivity c ont ribution s were observed in the plast ic cr y st all ine (C r y) and C ol h phases b y BD S .
The conductivit y contrib utions were an al y zed t o quantif y and to gain an understanding of the
conductivity mec h anism and hence an understanding of the mobilities of the ef f ecti ve ch ar ge
carri ers was obt ained in t he work . The temperature dependency of t he DC conductivit y ( 𝜎𝜎 𝐷𝐷𝐶𝐶 )
obtained from the anal y s is, showed that the struc tural changes occurring at t he phase transition
from the Cr y ph ase to Col h m esophase ar e r eco gniz ed as the chan ges in t he t empe rat ur e
depend en ce of the 𝜎𝜎 𝐷𝐷𝐶𝐶 . Thes e ch an ges wer e di scus sed b y dif feren t res tri ct ion s on t he cha r ge car ri er
mobilit y in Cr y and Col h phases o r a ch an ge in the ch arge t rans port me chan i sm .

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On the one hand, f or the non- ionic CLCs ( HAT6 , SHU09 , SHU12 , KAL465 and KAL468 ) it
is rev ealed t hat t he 𝜎𝜎 𝐷𝐷𝐶𝐶 changes b y appr ox im atel y 1 - 2 orders of magnitude at the pha se transition.
F or SH U10 such a change was not observed since as proofed b y XRD S H U10 do not form a Cr y
phase u pon cooling fro m its Col h mesophase. For SHU11 , a small chan ge in the temperature
depend en ce o f the 𝜎𝜎 𝐷𝐷𝐶𝐶 at the phase transition was found, therefore, t his observation implies smalle r
structural cha n ges at the phase transition for SHU11 compared to the structural change s fo r the
other non - ionic CL C s. The value of the phase transition enthalp y for the C ry - C ol h transition for
SHU11 was estimated to 0.3 kJ g -1 , which is qu ite smalle r than that for the other n on - ionic C LCs
(ca. 24 kJ g -1 - 52 k J g -1 ). This further e vi denced the smal ler st ruct ural ch a nges t akin g pl ace at th e
Cry -Col h phase transition for SHU11 . On the other, appr ox imatel y 4 orders of mag ni tude change
in the 𝜎𝜎 𝐷𝐷𝐶𝐶 val ues at the C ry -Col h phase transition were found for the ionic C LCs ( columnar I LC s
LC536 and LC537 ). This rel ativ el y bigger chan ge in the 𝜎𝜎 𝐷𝐷𝐶𝐶 val ues were a s soci ated wi th the
change in the charge transport mechanism from a delocalized electron hopping in the stacked
aromatic sy st ems (in the Cr y phase) to one dominated b y an ionic conduction in t he quasi - 1D ion
channels for m ed along the supramolec ular column s in the Col h m esop hase. Moreover, similar 𝜎𝜎 𝐷𝐷𝐶𝐶
valu es i n t he Cr y ph as e were found for the columnar ILCs compared to that for the non -ionic
C L C s, wh en th e s ame te m peratu re r an ge is considered for t he observed 𝜎𝜎 𝐷𝐷𝐶𝐶 . Ther efore, it might
be co ncluded for the no n - ionic CLCs that the charge t ransport mechanism is t he delocal iz ed
electron hopping in the Cry phase, and pre s umabl y the charg e transport m echanism is the same for
Col h phase with less restrictions on the charge carriers in Col h phase than in C ry phase. T h e
investigation of the conductivit y of the C LCs p res ented her e, im pl ies t hat the co lum nar I L C s s eem
to be more promisin g candidates for electronic applications due to their higher charge carrier
mobility . Furthermore, the study showed that the investiga t ed ILCs can be u sed as swi tch i n

124

applic ation , e.g. in field - effect transi sto rs , sin ce it was found an on/off rati o as high as c a. 10 4 for
thes e mater i als, wher e th e C ol h mesopha s e and in the Cry phase can be con sidered as on - state a nd
off - stat e r espe cti vel y.
In the second part of the thesis ( Chapter 5 ), a t riphen y l ene- bas ed DLC ( H AT6 ) was stu died
under nanoconfinement. HAT6 was confined into c y li ndrical nanopores of anodic aluminum ox ide
(AAO) and sil ica m embr anes havi n g pore siz es from 161 nm down to 12 nm (see Fi gu re 55). Th e
OPA and ODP A surface mo difi cati on wer e appl ied to control the molecular orderin g under t he
confinement. T h erefore, the h y drophilic inner wall s of the pores were successfully co ated wit h
alkyl c h ains b y t he, consequentl y , t he h y drophili c pore wa l l s were obtained. The phase behavior
ex plo red using D S C showed that the phase transiti on temperatures shift to the lower tem per atu res
and t he phas e tr ans iti on en thal pi es decr eas es w ith decre ase th e co nfi nem ent siz e. T he resu lts of
the phase behavior reveled here are important and should be considered for the application s at
nanoscale due to the considerable c h an ges in these properties under nanoconfinement. The
colle ctive orientation al o rder (dominating molecular order ing) of the mole cules of HAT6 under
the confinement was stu died using BDS. The investigation of the molecular orderin g using BDS
revea l ed that the domi nating planar axial order, is prerequisite for most of the electronic
applications, can be a chieved for HAT6 confi ned into the nanopor es of aluminum o x i de
membranes by the OPA and ODPA surface modif ications. Thus, it is concluded that the OPA and
ODPA mod ifications are pro mising strategie s for controllin g the molecular order in g of D L Cs
inside the nanopores of metal ox ide membranes. Moreo ver, th e sam ples di s cuss ed her e w ere also
furth er investiga t ed using temper ature - dependent optical birefrin gence (OB) and XRD in another
s t ud y. 163 Th e mole cular order in gs de termined by the dielec tric measurements found to be in
agree m ent with that determined by OB and XRD. Hence, the stud y h as demonstrated BDS as a

125

powerful method to monitor molecular order within the pores . It al so demonstrates a
well - esta blished investigation strategy for a study conce rnin g such a nanoconfinement.

Figure 55 . Graphical s ummary of the molecular ordering of H AT6 confin ed in to the cy lindrical n anocha nnels fo r t he
second

part o f the thesis.
The thesis has alread y provided an understanding of the molecular d ynamics of the KAL
compounds using BDS (dipole fluctuations per sp ective). Although, it has been demonstrate d in
this thesis that the combination of B DS and t he advance calorimetr i c techniques probing g lass
d y n amics are ben ef icial i n order to stud y glass d y n amics, an understanding of the glass y d ynamics
for KAL compounds using the calorimetr ic techniques ( entrop y fluct uations perspective ) is
missing. There fo re, t he next work will b e the inv estigatio n of the glassy d y n amics for the KA L
compounds using advance calorimetr i c techniques S HS and FSC.
As it has been repo rt ed in the lite rature 39 , 40 and also in the 0 work p res en ted h ere , multiple
glass y d y nami cs might take place in columnar liquid cry stalline s y stems due to the cooperative
fluctuations of cores and/or subst ituents in the intracolumnar and/or intercolum nar area. The d ipole

126

functionalization seems to be a good strategy t o probe s elect ivel y the glass dynamic s in the
intracolumnar or intercolumnar area using BDS b y a dipole functionalization of the molecules of
the cores or t hat of the substituents respectively. 37 , 39 , 40 , 64 , 70 The CL C s having onl y di pole
functionalized core and the same CLCs having on l y di po le function alized substituents as w ell as
the corresponding unfunc tionalized CLCs could be sy stematically investigated using BDS in order
to shed lig ht on the glassy dy n amics of C LCs as we l l as the glass transition phenomena. Moreover,
the m olecu lar d y nami cs o f C LC could al so b e s elect ivel y studi ed usi ng neutron scatterin g b y
partia ll y d euterating the molecule s of the core o r that of th e substituents. F urthermore, molecular
dy namics simulations could be a l so performed for both unfunctional and fu nctio n a l C LC s in o rder
to gain knowle d ge of the possi ble molecular motions. As it has been de m onstrated in this work,
such mole cular d y n amics simulations a re helpful for the assign ment of the molec ular d ynamic s
probe by BDS, SHS and/or FSC .
The investiga ti ons on the columnar ILCs prese nt ed in this st udy has reve aled that the IL Cs
seems to be more promising candidates t han the C L Cs fo r electronic ap plications due to their
higher charge carrier mobilit ies. To best of our knowledge this is the first study i nvestig ating the
mol ecular d y n amics of columnar IL Cs. Therefore, similar investig ations on differ ent columnar
IL C s having var y in g lengths of alkyl chains a nd counterions are n eeded t o create cu mul ati v e
knowledge of the structu re - d ynamics -conductivit y re l ationships for columnar ILCs. As discussed
also for C L Cs, such knowledge is required to explore columnar IL Cs ’ potential applications as
well as to desig n and t ail or their prope rties for the applications.
S everal studies has been reported, inve sti gating the phase be havio r and molecular ordering of
non- ionic CLCs conf i ned within the nanopores of me t al oxide membrane . 31 , 51 , 52 , 73 , 74 , 75 However,
to best of our knowledge such a stud y on colum nar ILCs confined into n anopores has not b een

127

report ed . Th erefo re, from both resear ch and appli cation point of view s the phase behavior and
mol ecular o rd erin g as w ell as con du cti vit y of co lum nar ILCs unde r nanoconfinement could be
intere sting to stud y . M oreover, local conductivit y of si ngle nanochannels of metal oxide
membranes filled with C L Cs could be studied to reveal the c ondu ctivit y of s ingle so - call ed
nanowire s. Th e loc al co n duct ivi t y can be m eas ure d using an A FM - based approach in the contact
mode, where condu ctive ti p and cantilever ar e used and an ex ternal frequ en cy - depe nd ent voltage
is applie d . 16 3F
164 Moreover, the measurement of the local conductivit y mig ht be performe d usin g a
broadband impedance microscope, which is a diel e ctric s pe ctro scop y - b ased techn iqu e as des cri bed
in ref . 164F 165.

128

APPEN DI X I
Matrix - Assi st ed L aser Des orp tion /I on izati on - Ti me of Fligh t (MALDI - T O F)
Matrix - Assisted L aser Desorption/Ioniza tion - Time of Fl i gh t (MA LD I) m ass spect romet r y
(MS ) ex perim ents wer e p erform ed to co nfi rm the chem ical stru ct ure of H AT 6 . Th e spe ctr a wer e
collected e m plo ying a Bruker Autofle x III (Bruker Daltonik GmbH, Br emen, Germany)
spectrometer equipped wit h a Smartbe am TM laser (356 nm, frequenc y 200 H z). The m easurem ent s
were p erform ed b y Dr. J an a Falkenh agen f ro m BAM (Bund es anst alt fü r Materi alfo rs chun g
und - prüfu n g (BAM ), Ri chard - Willstätter - S tr. 11, 12489 Berlin, German y ) . Fi gur e S 1 shows the
M A LD I - TOF MS spectr um of HAT6 . P ronounced peaks were observed in the theoretica l molar
mass range of 828 .63 g mo l -1 o f HAT 6 consider ing onl y the mass of 12 C. The di fferent pe aks ar e
detected due to the different is otopes of carbons; 12 C, 13 C, and 14 C. A mola r mass of HAT6 was
found to be 828.63 g mol -1 by taking into acc ount the natural occurrence of the isotopes.
820 825 830 835 840
14 C
13 C
Intensity [a.u.]
m/z [DA]
M HAT6 = 828.63 g mol -1
12 C

Figure S 1 . MALDI - TOF MS spectrum of HAT6 .

129

Th ermogra vi metric A n al ysi s (T GA)
Measu rement s and s am pl e prepar ati on fo r the m easurem ents ma y cause th erm al
dec ompositions of a sample . Thermal sta bilit y of the materials pr ese nted in this stu d y was
investigated using thermogr avimet ric anal y sis (TGA) in order to ensure that no therma l
dec omposition i s taking place.
Fi gu r e S 2 shows mass loss profile s of the monofunctionalized triphenylene derivatives
SHU09 -12 under synthetic a i r upon heating. Al l the samples shown in Fi gur e S 2 are the rm all y
stab le at least up to 533 K, which ensures that there was no thermal degradation during the sample
preparation and the measureme nt s .
400 600 800 1000 1200
0
20
40
60
80
100
∆ m [wt-%]
T [K]
T = 533 K SHU09
SHU10
SHU11
SHU12

Figure S 2. T GA c urve s fo r th e mo no func t io nali ze d t ri phe n yle ne d er iva ti ve s SHU0 9 - SH U12 . O ra nge l ine sho ws dat a
for

SHU0 9 , r ed line for SH U1 0 , gre en l i ne for SH U11 and pu rple line f or SHU12 .D as he d - dotted line represent s
t he
temperature, 533K, below which thermal decom

positio n of t he materia ls do no t occur.
Fi gu r e S 3 show s m ass l oss profiles of triph en y l ene crown eth er - b ased D LCs KAL465 and
KAL468 under s y nthetic air upon heating . All t ripheny l ene cro w n eth er - bas ed D LCs shown in

130

Fi gu r e S 3 are ther mally sta ble at leas t up to 5 0 3 K, which e ns ures that there was no ther m al
degrada t ion during the sa mple preparation and the measurements .
400 600 800 1000 1200
0
20
40
60
80
100 KAL465
KAL468
∆ m [wt-%]
T [K]
T = 503 K = 230°C

Figure S 3 . T GA cur ve s for tr ip hen yle ne cro wn et her - based liquid cr y stal s KAL 465 and KAL468 as indicated .
Dashed

line represent s the temperature, 5 03 K, below whi c h th ermal dec o mpos ition of the ma terials do not occ ur.
T he filling degree of the membranes with HAT 6 was cont roll ed b y TG A. TGA m easu rem ents
were carried out b y a Seiko TG/DTA 220 with a heating rate of 10 K min - 1 , from room 303 K to
1000 K, under sy nthetic air to burn all org anic com pound confined into the nanopores. Fi gu r e S4
shows TGA curves for bulk H AT6 , the confined HAT 6 in unmodified , OPA - and ODP A - modifie d
AAO mem br anes as well as th e mod ifi ed empt y mem brane s . All samples s hown in Fi gure S 4 are
thermally sta bl e at least up to 550K, which ensures that ther e was no thermal deg r adation during
the s ampl e prep arat ion and the measurements. From the es timated masse s , the degree of filling
can be estimated. Complete pore filling was obtained for a l l samples shown in thi s stud y .

131

400 600 800 1000 1200 1400 1600
0
20
40
60
80
100
H AT6 i n OP A- m od. 73 nm
O PA-m od. 73 nm
R es i due
AAO
Burned organi c
com pound
O DP A- m od. 73 nm
H AT6 i n OD PA-m od. 73 nm

∆ m [w t-% ]
T [ K]
HA T6 i n 73 nm
Bul k HAT6

Figure S 4 . T GA c urve s for HA T6 in the bu lk (black solid line) , H AT6 c o nfine d in to unm odifie d AAO m embrane
(green solid line),

HA T6 confin ed into OD P A - modi fied AAO m embran e (blue sol id line as in dicated) , e m pt y OD PA
-
m o di fied AAO me mbranes (b lue solid line as i ndicate

d), H AT6 co nfi ned into O PA -
modified AAO membrane (red
dashed line as indicated), empty OPA

-
modified AAO membranes (red dashed line as indicated). TGA curves given
in here for t he mem branes havin g the por e size of 73 nm .

Attenu ated T otal R efl ecti on Fouri er Tran sf or m In f rared Sp ectrosco py (ATR - FT I R )
Att enuat ed total refle ct ion Fourier transform infrared s pe ctrosco p y (ATR - FT IR) w as
employe d to con firm the surface m odification of the membranes. The m easurements of empt y
unmodified and modifi ed mem branes were c arri ed out at roo m t emperat ure . P eaks fo r the al k y l
C- H stretching should appea r fo r the FTIR spectra of the modified membranes, and its appe ar ance
can be use d as an indication to confirm the OPA- a n d ODPA -modifications. Fi gu r e S 5 shows that
the peaks at 2850 cm -1 and 2930 cm -1 , co rresponding to s y mmetric and antis y mmetric alky l C- H
stretching r espectivel y appear for the modified empt y m embranes (red and blue lines). As it is
expected, these peaks were not observed in FTIR spectra for the unmodi fied membranes (black
lines) .

132

4000 3500 3000 2500 2000 1500 1000 500
73 nm - OPA
17 nm - OPA
73 nm - ODPA
73 nm
17 nm - ODPA
sym. C-H st retching, 2850 cm
-1
asym. C-H st retching, 2930 cm
-1
Transmission
[
a.u.
]
Wavenumber
[
cm -1
]
17 nm

Figure S 5 . FTIR spectra of the OP A - and O DPA - modif ied as well a s unm odified al uminum o xide mem branes as
indicated .

Sma ll Angle X - ray Sca t teri ng (S AXS)
Lon g - range o rderi n g was s tu died b y smal l an gle X - ra y scattering ( SAXS) in the “MAUS” : a
heavily customiz ed Xeuss 2.0 (Xenocs, France). X- ra ys ar e generat ed fro m a m icrofo cu s X - r a y
tube w ith a copper targe t, followed b y a multila y er optic to par allelize and m onochroma tiz e the X -
ray b eam to a wavelength of 0.154 nm. The detec tor consists of an in - vacuum motorized Eiger
1M, for this investigatio n placed at distances of 208, 558, a nd 1258 mm from the sample. Af ter
correction, the data from the different distances are combined into a single c u rve. The space
between the s tart of the colli mation until the detector i s a continuous, uninterrupted vacuum to
reduce b ackground. The m embranes ( di scs) were mounted with their surface perp endicular to the
beam i n th e ev acuat ed s am pl e chamb er. Th e r esu lti ng data h as been pro ces s ed us ing th e D AWN
software package 124 , 125 with the following processing ste ps in order: masking, correction for
counting time, dar k - curr ent, transmission, primary be am flux, background (no sample in the
beam), fl at - field, polariza tion and solid an gle, followed b y azim uthal averag i ng. The dat a has not

133

been sca l ed to absolute units. P hoton counting uncertainties were estimated from the raw image ,
and propagated through t he correction steps. For t he alignment experiment, the membrane was
held upright be t ween two LEGO bricks, on top of a Ph y sik Instrumente H811.I2V hexapod. 200
second exposures were taken at various tilt angles, to se ek the tilt angle that would produ ce a
radia ll y isotropic patter n.
10
-2
10
-1
10
0
10
1
10
0
10
1
10
2
10
3
10
4
10
5
10
6
10
7
10
8
10
9
10
10
10
11
Intensity [a.u.]
q [ nm
-1
]

Figure S 6. SA XS patt erns of u nmodifi ed (black ) and ODP A - m odi fi ed (red) AAO m e mbr anes wi t h 38 nm diamet er
pores as well as that of

HA T6
confined AAO membranes with 38 nm por e size (blue). The curves are shifted along
the y

- scale f o r clarity.
Fi gu r e S 6 shows the SA XS patterns of the samples. It is concluded that the pores are 100%
fill ed for HAT 6 confined into AAO with 38 nm pore diame te r .

134

APPEN DI X II – Supporting In formation fo r Sectio n 4 .1
POM Tex tu res

Figure S 7. POM textures of SHU09 at 408 K (lef t), at 398 K (m iddle) an d at 365 K (ri ght) u pon cooli ng from the
isotro pic liquid (co oling ra te 5

K mi n -1 , magni ficati on 200x) sh o wing p seu do focal conic f a n -
sha p ed text ur e s a nd
de ndr i meri c gr o wt h te xt ure s.

Figure S 8. POM textures of SH U10 at 499 K (lef t), at 436 K (m iddle) an d at 383 K (ri ght) upo n c oo li ng fr o m the
isotro pic liquid (cooling rate 5

K min -1 , magnif icati o n 200x) s howing dendrim eric g ro wth and pseudo f ocal c onic fan
-
shaped textures .

Figure S 9. POM textures of SH U11 at 447 K (left ) at 436 K (m iddle) an d at 368 K (right) up on c o ol in g fro m t he
isotro pic liquid (co oling

rate 5 K mi n -1 , magn if ic ati o n 20 0 x) sho wing d e ndr i meri c gr o wt h t ext ure s .

100 μ m

100 μ m

100 μ m

100 μ m

100 μ m

100 μ m

100 μ m

100 μ m

100 μ m

135

Figure S 10 . POM textu res of SHU1 2 at 373 K (left ), at 365 K ( mi ddle) an d at 346 K (rig ht) upon cooling from the
isotro pic liq uid (co oling ra

te 5 K mi n -1 , magnificatio n 2 00 x) s ho win g de ndri mer ic gr o wth a nd
pseu do foca l conic
fan

- shaped textures .

XRD Data and Diffraction Patterns
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
Intensity [a.u.]
q [Å
-1
]

Figure S 11 . WA XS diff ractogram of SHU09 at 363 K w ith the c orrespondi ng dif fract io n pat tern (i nset).

100 μ m

100 μ m

100 μ m

136

0.2 0.4 0.6 0.8
Intensity [a.u.]
q [Å
-1
]

Figure S 12 . SAXS d i ffr a ct o gr a m of SH U09 at 3 63 K with the co rre sponding di ffractio n patter n (inset).

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
Intensity [a.u.]
q [Å
-1
]

Figure S 13 . WA XS diff ractogram of SHU10 at 353 K w ith the c orrespondi ng dif fract io n pat tern (i nset).

137

0.2 0.4 0.6 0.8
Intensity [a.u.]
q [Å -1 ]

Figure S 14 . SAXS d i ffr a ct o gr a m of SH U10 at 3 53 K with the co rre sponding di ffractio n patter n (inset).

0.2 0.4 0.6 0.8
Intensity [a.u.]
q [Å
-1
]

Figure S 15 . SAXS d i ffr a ct o gr a m of SH U11 at 3 53 K with the co rre sponding di ffractio n patter n (inset).

138

0.2 0.4 0.6 0.8 1.0 1. 2 1.4 1.6
Intesity [a.u.]
q [Å -1 ]

Figure S 16 . WA XS diff ractogram of SHU12 at 353 K w ith the c orrespondi ng dif fract io n pat tern (i nset).

0.2 0.4 0.6 0.8
Intensity [a.u.]
q [Å
-1
]

Figure S 17 . SAXS d i ffr a ct o gr a m of SH U12 at 3 53 K with the co rre sponding di ffractio n patter n (inset).

139

Dif f erenti al S can nin g Calori metry (DS C)
Conventional DSC measurements of SHU10 , SHU1 1 , S HU12 and H AT5 were car ried out at
temperatures down to 17 3 K under nitrogen pur ge. DSC traces of SH U10 , SHU11 , S HU12 and
HAT5 measured under nitrogen purge are given in F i gu r e S 18-S21 . In addition, conventional DSC
measureme nt s of the com pounds were a l so conduct ed at tempera t ures down t o 103 K under helium
purge (see Fi gur e S 22 ). Th e me asurem ent s were per formed i n t he temp era t ure r an ge from 103 K
to 303 K with a he ating/cooling rate of 10 K min - 1 . Hel iu m was used as a purge gas at a fl ow rat e
of 20 ml min -1 . Similar t o the m easu rement s performed unde r nit rogen purge, baseline
measu rement s w ere con du cted b y m easuri n g an em pt y 50 µl alum inu m pan und er the s am e
conditions. The baselines we re subtracted from the data measured for the samples. The calibration
of th e DSC was ch eck ed before t h e measurement b y measuring an indium standar d.

Figure S 18 . DSC t her m o grams o f SHU10 fo r the fir st co ol in g and t he se co nd hea ti n g ru n a t a hea ti ng/ co ol i ng ra te
of 10 K

mi n -1
. Dashed lines po int out the phase transition tem perat ures observed during the second heating run .
Dotted line indicate s the glas s tr ansition te mperat ure ob serve d duri ng t he se co nd he ati ng r u n .

140

Figure S 19 . DSC the r mogr a ms of SH U11 for the first coo ling and the seco nd heating ru n at a heatin g/coolin g rate
of 10 K

mi n -1
. Da shed li ne s p oi nt o ut the p ha se tr a nsi t io n t e mper at ure s o bse r ved dur i n g the se co nd hea t in g ru n.
Dotted line indicate s the glas s tr ansition te mperat ure ob serve d duri ng t he se co nd he ati ng r u n .

Figure S 20 . DSC t her m o grams o f SHU12 fo r the fir st co ol in g and t he se co nd hea ti n g ru n a t a hea ti ng/ co ol i ng ra te
of 10 K

mi n -1
. Dashed lines po int out the phase transition tem perat ures observed during the second heating run .
Dotted line indicate s the glas s tr ansition te mperat ure ob serve d duri ng t he se co nd he ati ng r u n .

141

Figure S 21 . DS C the r mo gra m s o f HA T5 for the first cooling and the second heating run at a heat in g/cooling rate of
10 K

mi n -1
. Da s hed li nes p o in t o ut the pha se t ra nsit io n t e mpe ra tur es o b ser ved d ur ing the se co nd hea tin g r un. D ot ted
line indica tes the gla ss tra nsition te mperature o bserved duri ng t he se co nd he at i ng r u n .

Figure S 22 . D SC the r mogr a ms o f SHU1 1 - SHU1 2 a nd HA T5 for the second heat ing run at a h eating rate of
10

K mi n -1
at lo w te mperatur es. So lid lines po int out the glass transition te mperature s obser ved during the second
heat i ng r un.

Broa db an d Di electri c Sp ectrosco py (BDS )
The rel ax atio n map s, co n tain ing th e d ata fo r S HU09 -12 and HAT 5 as wel l as th e data t aken
from t he l iterat ure for t h e relat ed relax at ion proc ess es, ar e giv en i n Fi gur e S 23 and Fi gu r e S 24.
VFT par amet ers ob tain ed f rom VFT -equation (eqn. (2)) fits and ac tivation energie s estimated f rom

142

Arrhenius-equation (eqn. (1)) fi ts a re pr es ented in Tab le S 1 . Furthermore, the plot of the lattice
spaci ng ver sus t he re lax ation rates of γ - pro cesses at chosen temperature is shown in Fi gu r e S 25.

2 3 4 5 6 7 8
-4
-2
0
2
4
6
8
10
α 1
α 2
γ
log(f max [Hz])
1000 / T [K -1 ]
SHU09
SHU10
SHU12
SHU11
PE
HAT5

Figure S 23 . Com bined relax ation ma p of SH U09 - SHU 12 co nstru cted fro m data obtained b y BDS, Flash DSC and
DSC . Orange symbols

– data for SHU0 9 ; red s ymbol s – da ta for SHU10 ; gre en symb o ls – data for SHU11
; purple
sym bols

– data for SHU12 ; and blue sy mbols – d ata for HA T5 . T r iangl es – α 1 - relaxations (BDS); open circles – α 2
-
relaxation (B DS); fi lled sq uare s

– γ - rela xatio ns (BDS); o pen stars – α 1 - rela xatio ns (FSC); open pen ta gons
–
α

2 - relaxatio n (SHS); and filled stars – ther mal gla ss
tra nsition te mperature s (DS C). S olid lines ar e the fits o f
VFT

- equa tio n (e qn. (2) ) to the data. Dashed line s are the fi t s of the Arr he niu s - equatio n (e qn. (1))
to the data. Black
filled tr iangle s d enote the d iel ectric α

- relaxation of polyethylene t ake n from ref. 145
. B la ck he xago ns sy mb ol iz e the
dielectr ic

γ - relax atio n of polyethylene taken fro m ref. 40 . Black cro sses r epresent the c alorimetric α -
relaxatio n of
po lyet h ylene take n fro m r e f.

146 . Black open h e xagons symbolize the dielectric
β

- rel axati on of poly ( n -
de c yl
methacrylat e) ta ken from ref. 147 .

143

2 3 4 5 6 7 8
-4
-2
0
2
4
6
8
10
THA11
α
1
α
2
γ
log(f
max
[Hz])
1000 / T [K
-1
]
SHU09
SHU10
SHU12
SHU11
Tri 11
HAT5

Figure S 24 . Com bined rel axation map of SHU09 - SHU1 2 constructed from data obtained b y BDS, Flash DSC and
DSC . Orange symbols

– data for SHU0 9 ; red s ymbol s – da ta for SHU10 ; gre en symb o ls – data for SHU11
; purple
sym bols

– data for SHU1 2 ; blue s ym bols – d ata for H AT5 ; cya n blue sym bols – data for Tri1 1 ta ke n fr o m r e f. 144
;
and g ray sym bol s

– da ta fo r THA 11 taken f ro m ref . 144 . T r ia ngles – α 1 - relaxatio ns ( B DS ); op en p e ntago ns
–
α

2 - relaxat io n (SHS); open circles – α 2 - r ela xation (B DS); filled square s – γ - relaxa tions ( BDS) ; ope n stars – α 1
-
relaxation s (FSC); and f illed stars

– ther mal glass transi tion te mperature s (DSC). So lid lines are the fits o
f
VFT - equation (e q n. (2)) to the data. Dashed line s are the fit s o f the Ar rhe ni us - eq ua t io n (e qn. (1) ) to the data .

Table S 1 . VFT p aramet er s and activation energies obtained f r om VFT - a nd Ar rhe ni us - equ ations fits
Co mpound

Process

Depende nce

log (f

∞
[H z ])

T

o
[K]

E

A
[ kJ mo l - 1 ]

SHU0 9
α 1

VFT

9.1 ± 0.1

184.5 ± 1.2

-

α 2

VFT

12.0 ± 0 .3

91.2 ± 2 .2

-

γ

Arrhe nius

12.0 ± 0 .1

-

19.2 ± 0 .1

SHU1 0
α

1
VFT

9.0 ± 0.2

172.5 ± 1.3

-

α

2

VFT

10.8 ± 0 .1

93.5 ± 1 .4

-

γ

Arrhe nius

11.7 ± 0 .1

-

17.0 ± 0.3

SHU1 1
α

1
VFT

12.0 ± 0 .3

163.3 ± 4.7

-

α

2
VFT

10.3 ± 0 .1

114.8 ± 0.4

-

γ

Arrhe nius

9.1 ± 0.2

-

11.9 ± 0.6

SHU1 2
α

1

VFT

12.0 ± 1.3

190.5 ± 11.6

-

α

2

VFT

12.0 ± 0 .9

73.1 ± 7 .5

-

γ

Arrhe nius

13.1 ± 0 .4

-

25.6 ± 1.0

HAT5
α

1

VFT

12.0 ± 1 .0

147.5 ± 9.3

-

α

2

VFT

10.2 ± 1 .1

85.8 ± 12. 2

γ

Arrhe nius

13.6 ± 0 .1

-

26.1 ± 0.2

144

19.6 19.8 20.0 20.2 20.4 20.6
3.0
3.5
4.0
4.5
5.0
5.5
6.0
HAT5
SHU12
SHU11
SHU09
log(f max, γ [Hz]) at 147 K
Lattice Spacing [ Å]
SHU10

Figure S 25 . Relax atio n rates of γ - processes at 147 K versus lattice spacing for SHU0 9 - SH U12 and HAT5 as
indicated. The arrow is a gui d e for the eye.

Fast Scanning Calorimetr y ( FSC)
200 220 240 260 280 300 320
5000 K s
-1
2000 K s
-1
10000 K s
-1
500 K s
-1
1000 K s
-1
200 K s
-1
100 K s
-1
20 K s
-1
10 K s
-1
Heat Flow [a.u. ]
T [K]
50 K s
-1
Endo

Figure S 26 . F SC ther m o gra ms of SH U09 for heatin g runs at different heating rates as indic ated. Dashed lin es indicate
the thermal glass tra nsition te mperat ures esti mated.

145

200 220 240 260 280
Heat Flow [a.u. ]
T [K]
100 K s -1
10 K s -1
20 K s -1
50 K s -1
Endo

Figure S 27 . F SC ther m o gra ms of SH U11 for heatin g runs at different heating rates as indic ated. Dashed lin es indicate
the thermal glass tra nsition te mperat ures esti mated.

200 220 240 260 280 300 320
Heat Flow [a.u. ]
T [K]
10 K s
-1
20 K s
-1
50 K s
-1
100 K s
-1
200 K s
-1
500 K s
-1
1000 K s
-1
2000 K s
-1
Endo
10000 K s
-1
5000 K s
-1

Figure S 28 . FS C t her mogr a m s o f SHU1 2 for heating runs at d iff erent heating rates as i ndic ated. Dashed lin es indicate
the thermal glass tra nsition te mperat ures esti mated.

146

180 200 220 240 260 280 300 320
2000 K s -1
500 K s -1
1000 K s -1
200 K s -1
100 K s -1
20 K s -1
10 K s -1
Heat Flow [a.u. ]
T [K]
50 K s -1
Endo

Figure S 29 . FS C t her mo gr a ms o f HAT5 for heat ing runs at dif ferent heating rates as in dicated. Dashed lines i ndicate
the thermal glass tra nsition te mperat ures esti mated.

APPENDIX III – Supporting In formation for Sec tio n 4.2
Table S 2. V FT par am eters a nd activatio n ener gies ob tained fro m VFT - a nd Arr he ni us - equatio ns fits
Co mpound

Process

Depende nce

log (f

∞
[H z ])

T

o
[K]

E

A
[ kJ mo l - 1 ]

KAL465
α

1
VFT

8.1 ± 0.2

240.3 ± 5 .7

-

α

2

VFT

12.0 ± 2 .5

141.5 ± 24. 3

-

γ

Arrhe nius

13.9 ± 0.1

-

29.2 ± 0.0

KAL468
α

1
VFT

8.0 ± 0.3

226.0 ± 1 4.9

-

α

2

VFT

12.0 ± 1.2

116.5 ± 1 6.2

-

γ

Arrhe nius

13.1 ± 0.1

-

28.2± 0. 1

147

2 3 4 5 6 7 8
-4
-2
0
2
4
6
8
α 2
HAT5
PE
α 1
log f [Hz]
1000/T [K -1 ]
γ -relaxations
α 3
KAL465
KAL468
Cry
Col h

Figure S 30 . Combined relaxation m ap o f KAL 465 , K AL4 68 a nd H AT5 . T he data for HAT5 t aken f ro m the research
wor k pr ese nted i n

Secti on 4.1 . Red sym bols – data for KAL465 ; blue sym bols – data for KAL468 ;
and gra y s ymb o ls
–

data for HAT5 . O pe n t ria n gles – α 1 - relaxat ions (BDS) ; Filled trian gles – α 2 - rela xatio n (BDS) ; open squar es
–
γ

- relaxatio ns (B DS); filled st ars – α 1 - relaxa tions (F SC); open pent agons – α 2 - relaxation (SHS); and open sta rs
–
thermal gla ss transitio n te mper atures (DSC).

Bl ac k a nd o r ange s ol id lines ar e the fits of VFT - eq uati on ( e qn. (2)
) to
the data

for KAL compounds and HA T5 respectively . Black and orange d ashe d li ne s are
the fit o f the
Arrhe nius

- equa t io n (e qn. (1 ) ) to the data fo r KAL compou nds and HAT5 respectively . Dar k y e llo w filled
circles
denote th e dielectric α

- rela xati on o f p ol yeth yl e ne ta ke n fr o m re f. 145 . Dark y el low
hexagons sym b olize the dielectric
γ

- rela xatio n o f p ol yet h yle ne ta ken fr o m re f. 40 . Black crosses represent the calorimet r ic α -
relaxation o f po lyeth ylene
ta ken fr o m re f.

146 . Black op en hexagons symbolize the dielectric
β

- rel a xat ion of pol y ( n -
decyl methacrylate) taken
fro m r e f. 147 .

2.4 2.8 3.2 3.6
-16
-15
-14
-13
-12
-11
-10
-9
KAL468
KAL465
SHU12
HAT6
log ( σ DC [S cm -1 ])
1000/T [K -1 ]
SHU09
SHU10
SHU11

Figure S 31 . Tem per ature dependencies of th e 𝜎𝜎 𝐷𝐷𝐶𝐶 gi ve n fo r sec o nd hea tin g r un fo r d iffe re nt D LCs as i nd ic ate d .

148

APPEN DI X IV – Supporting I nformation for Sec tio n 4.3
Havriliak -N egami (HN) f unction to the experimental data
-1 0 1 2 3 4 5 6 7
-2.3
-2.2
-2.1
-2.0
-1.9
log ε ''
log (f [Hz])
133 K
153 K
173 K

Figur e S 32 . Frequency dep endency of dielectric l o ss of LC53 7 for the second heat ing at different tem perat ures as
indicated . Solid lines de note the fit b y the HN - fun c tion to the corres pondin g data .

-2 -1 0123456
-2.3
-2.2
-2.1
-2.0
-1.9
-1.8
-1.7
-1.6
-1.5
243 K
249 K
257 K
log ε '' deriv
log (f [Hz])

Figur e S 33 . Frequ ency depen dency of 𝜀𝜀 𝑑𝑑𝑑𝑑𝑑𝑑𝑖𝑖𝑑𝑑
′′ of LC537 for the s eco nd heating at the indicated tem p eratures
( α - proce ss). Solid lines are the fits of the HN - func t io n gi ve n in eq n. ( 19 ) to the data .

149

Add iti on al ex peri menta l resu lts
180 200 220 240 260 280 300
40
60
80
100
120
U
R
[µV]
T [K]
160 Hz
80 Hz
40 Hz
20 Hz

Figur e S 34 . T em p erature dependence of the real part o f the complex differential voltage of LC537 during the cooli ng
run at diff ere nt frequencies as indicated. Black arrow - guide for th e e y e s.

Fitting p ara mete rs of VFT - and Ar rhenius - equations f itt ing to the con duc tivity data
VFT parameters and activation ene rgies e stima ted fr om the fitting s to the c onductivity
processes pr ob ed b y BDS is given in Table S1. It is worth to note that the VFT fitting parameters
are given onl y for t he cool ing runs due to the broader tem perature range obtained for the 𝜎𝜎 𝐷𝐷𝐶𝐶 v alues
for the coolin g runs. M oreover, l og(σ ∞ [S cm -1 ]) was f i xed to 1.3 for the cooling run of L C537
sin ce th e broad er t emp erat ure ran ge i s o btai ned f or t he 𝜎𝜎 𝐷𝐷𝐶𝐶 values for LC536 , and log(σ ∞ [Hz])
was found to be 1.3 ± 0.2 from free fitting of VFT-equa t ion (eqn. (2)) to th e d ata fo r LC536 .
Table S 3. VFT p aram eters a nd activation energies estimated fro m the fittings to the BDS data. To reduce the n u mber
of free fit parameters, log ( σ ∞ [Hz]) w as fix ed to 1.3 for LC537 .
Co mpound R un
VFT (Col

h
phase)

Arrhenius (Cry

1
phase)

log (σ

∞
[S cm -1 ])

T

o
[K]

log (σ

∞
[S cm -1 ])

E

A
[ kJ mo l - 1 ]

LC536
1 st Heating
-

-

2.4 ± 0.4

87 ± 2

1 st Cooling
1.3 ± 0.2

179 ± 3

2.3 ± 0.6

87 ± 3

2 nd Heating
-

-

2.6 ± 0.4

89 ± 3

LC537 1 st Heating
-

-

1.3 ± 0.6

85 ± 5

150

1 st Cooling
1.3

168 ± 2

1.2 ± 0.5

83 ± 3

2 nd Heating
-

-

1.2 ± 0.3

84 ± 2

151

APPENDI X V – Suppo rting In formation for Chap ter 5
P hase Beha vior Unde r Confinem ent by DSC
ODPA modifications of the nanopores causes ca. 4.4 nm decr ease in the diamete r of the pores
for th e empt y membr an es. Nevertheless, thickness of the ODPA - modification could not be
measu red for t he HAT 6 fil led coated pore s. Theref ore, Fi gu re S 35 shows the dependencies of the
phase transitions temperatures and enthalpies on inverse pore size , consid ering the narrowing of
the pore size for OD P A - modified samples. Compar ing the dependencies shown in Fi gu re 52 an d
Fi gu r e S 35 , it is concluded that the po re narrowing has no considerable e ffect on our discussions
based o n th ese d epen den cies .
0.00 0.02 0.04 0.06 0.08 0.10
10
20
30
40
50
0.00 0.02 0.04 0.06 0.08 0.10
325
330
335
340
345
1/d
[
nm -1
]
∆Η
Cry-Colh
[J/g]
pSi5
b)
a)
pSi5
T
Cry-Colh
[K]
1/d
[
nm
-1
]
σ
ODPA
= 5.1 mN/m
σ
Unmod
= 5.4 mN/m

0.00 0.02 0.04 0.06 0.08 0.10
0
1
2
3
4
5
6
7
8
0.00 0.02 0.04 0.06 0.08 0.10
350
355
360
365
370
375
d)
1/d
[
nm
-1
]
pSi5
∆Η
Colh-Iso

[J/g]
c)
σ
Unmod,2
= 0.8 mN/m
σ
Unmod,1
= 2.2 mN/m
T
Colh-Iso
[K]
1/d
[
nm
-1
]
σ
ODPA
= 0.9 mN/m

Figure S 35 . Inv er se pore size dependencies of t he phase transition enthalpies for (a) the Cry - Colh t ra ns iti on a nd ( c)
the Co l h

- Iso tran sition, a s well a s that of the phase tr ansition te mperatures for (b ) the Cry -
Co lh t ra nsit io n a nd ( d ) t he
Colh

- Iso tran sition. Blue s squares indicate data f o r bulk HAT6 , black symbols indicate data f o r HA T6
co nfi ned into
unm odified m e mbra nes and red sy mbols in dicate da ta for

HAT6 confin ed into ODPA -
m o dified membra nes (f illed
circles: main peak, open symb ols: satell i te peak). Dashed

- do tt
ed lines are g uide for e yes. So lid line s are t he fits o f
eqn . ( 32 ) to the dependen cies.

152

Coll ectiv e Orien ta ti ona l O rder b y DS
DS investigations showed unusually the pha s e transi tion takes place in seve ral steps for HAT6
confined into the ODP A - modified nanopores of AAO membrane wit h a pore size of 47 n m.
Therefo re, the DS resul t for t hese s ampl es i s r epr e sent ed in Fi gu r e S 36 in o rder to show the steps
clearl y .
345 350 355 360 365 370 375 380
0.97
0.98
0.99
1.00
1.01
∆ε positive
Normalized ε '
T [K]
47 nm - ODPA
Col h Iso

Figure S 36 . No rmalized diele ctric p ermitivities as a f unction of te mperature durin g the third heatin g run for the sa mple
with a pore size of 4 7 nm with m o dified por e w alls. T he dash ed

- dotted lines indica te t he Co l h - Iso
phase tra nsitio n
temperatures d etermined b y DSC.

The dashed li nes represent temperature dependencies of ε′ extrapolated from Col
h
and I so p hase s.

In some cases from the o verview given in Fi gure 11 i t i s hard to detect whether Δε is positive
or ne gativ e. Th eref ore, en lar ged fi gures a re pr ep ared fo r so me s ampl e an d giv en in Fi gure
S6 - Figu re S 41.

153

350 355 360
0.986
0.988
0.990
17 nm
Normalized ε '
T [K]
Col h Iso
∆ε positive

Figure S 37 . No rmalized diele ctric p ermitivities as a f unction of te mperature durin g the third heatin g run for the sa mple
w ith a pore s ize of 17 nm w ith unmodi fied pore w alls. T he dash ed

- dotted lines indicate the Col h - Iso
p has e tr a nsi t io n
temperatures d etermined b y DSC

. T he dashed li nes represent temperature dependencies of ε′ extrapolated from Col
h
and I so p hase s.

350 355 360 365
0.984
0.986
0.988
0.990
Normalized ε '
T [K]
∆ε positive
Iso
Col
h
18 nm

Figure S 38 . No rmalized diele ctric p ermitivities as a f unction of te mperature durin g the third heatin g run for the sa mple
w ith a pore s ize of 18 nm w ith unmodi fied pore w alls. T he dash ed

- dotted lines indicate the Col h - Iso
p has e tr a nsi t io n
temperatures d etermined b y DSC

. T he dashed li nes represent temperature dependencies of ε′ extrapolated from Col
h
and I so p hase s.

154

345 350 355 360 365 370
0.980
0.982
0.984
0.986
0.988
0.990
0.992
Normalized ε '
T [K]
Col h Iso
24 nm

Figure S 39 . No rmalized diele ctric p ermitivities as a f unction of te mperature durin g the third heatin g run for the sa mple
w ith a pore s ize of 24 nm w ith unmodi fied pore w alls. T he dash ed

- dotted lines indicate the Col h - Iso
p has e tr a nsi t io n
temperatures d etermined b y DSC

. T he dashed li nes represent temperature dependencies of ε′ extrapolated from Col
h
and I so p hase s.

350 355 360 365
0.980
0.982
0.984
0.986
0.988
∆ε positive
Normalized ε '
T [K]
34 nm
Col
h
Iso

Figure S 40 . No rmalized diele ctric p ermitivities as a f unction of te mperature durin g the third heatin g run for the sa mple
w ith a pore s ize of 34 nm w ith unmodi fied pore w alls. T he dash ed

- dotted lines indicate the Col h - Iso
p has e tr a nsi t io n
temperatures d etermined b y DSC

. T he dashed li nes represent temperature dependencies of ε′ extrapolated from Col
h
and I so p hase s.

155

360 365 370
0.986
0.988
0.990
0.992
0.994
Normalized ε '
T [K]
38 nm - ODPA
Col h Iso
∆ε positive

Figure S 41 . No rmalized diele ctric p ermitivities as a f unction of te mperature durin g the third heatin g run for the sa mple
with a pore size of 3 8 nm with m o dified por e w alls. T he dash ed

- dotted lines indica te t he Co l h - Iso
phase tra nsitio n
temperatures d etermined b y DSC.

The dashed li nes represent temperature dependencies of ε′ extrapolated from Col
h
and I so p hase s.

156

APPENDI X VI
Lis t of Abb rev iation s, Sym bols an d Con stant s
List of Abbreviations
LC

Liq uid cr y stals

C LC

Columnar liquid crystal

D LC

Discotic liquid crystal

ILC

Ionic l iquid cr y st al

BDS

Broa db and dielectric spectroscop y

SHS

Speci fic h eat sp ect rosco p y

FSC

Fast s canni ng calor imet r y

DSC

Diff erential sca nnin g calorimetry

TMDSC

Temper atur e mo dul ated d iffere ntial s cann in g calor imetry

SSDSC

St epScan d ifferentia l scanning ca lorimetr y

1D

One dimensional

2D

Two dimensional

3D

Three dimensional

POM

Polarizing optical mic roscopy

XRD

X- ra y di f fracti on

TGA

Therm o gravimet ri c anal ysis

FT IR

Fourier t ransform infrare d spectroscopy

ATR

Attenu ated total ref lection

SAXS

Small ang le X - ray Sc attering

WAXS

Wi de angle X - ray Scatte r ing

MAUS

Multi - scale anal y z er fo r ul trafi ne st ructu res

M A LD I - TO F

Matrix - as sisted laser des orption/io niz ation - t ime of flig ht

LR T

Linear response theory

HAT6

Hex akis hex y l ox y tri phen ylen e

HAT5

Hexakispentyloxy t riphenylene

HATn

Hex akis (n - alk y lox y )t ri phen ylen es

SHU09

Pent apent ylox y tri phen y l en e car r ying eth y l gl y col at e uni t

SHU10

Pentapenty l ox ytriphe n y l ene carrying hexanoyl unit

SHU11

Pentapenty l ox ytriphe n y l ene carrying trifluorome t h yl unit

SHU12

Pentapenty l ox ytriphe n y l ene carrying ethyl diethyleneglycol unit

KAL465
Trip hen ylene crown eth e rs - based un s y mmetrical disco tic liquid

crystal having alkyl chains consist of 9 car bons
KAL 468
Trip hen ylene crown eth e rs - based un s y mmetrical disco tic liquid

crystal having alkyl chains consist of 12 car bons

157

LC536
Lin e ar sha p ed tetr ameth ylate d guanidinium - based ionic liquid crystal

with counteranion triflate having alk y l chains consist of 14 carbons
LC537
Lin e ar sha p ed tetr ameth ylate d guanidinium - based ionic liquid crystal

with counteranion triflate having alk y l chains consist of 16 carbons
OTf

Trifla te anion

PE

Pol y eth y l en e

AAO

Anodic aluminum oxide

OPA

n-Octcylphosphonic acid

ODPA

n-Octadecylphosphonic acid

Cry

Plastic c r y stalline

Col

h

Hex agonal co lum nar

Is o

Isotropic

DC

Direct cu rrent

List of S ymbols
D

Diel ectric d isp lac emen t

𝜀𝜀 ∗

Complex dielectric funct ion

𝜀𝜀′

Real p art o f the com plex d iel ectric f un cti on

𝜀𝜀 ′′

I ma ginary pa rt of the complex dielectric function

𝜀𝜀 𝑑𝑑𝑑𝑑 𝑑𝑑 𝑖𝑖𝑑𝑑
′′

Conduction- free di el ectri c l oss

E

Elec tric field

P

Polarizatio n

𝜒𝜒 ∗

Complex die lectric susceptibility

𝜔𝜔

Angular frequency

𝑓𝑓

Frequ enc y
𝛿𝛿

Phas e shi ft

𝜏𝜏

Relaxation time

∆𝜀𝜀

Diele ctric strength

H

Enthalpy

c

p

Speci fic h eat capa cit y

Δc

p

Chan ge in sp eci fic h eat cap acit y

𝑐𝑐 𝑃𝑃 ∗

Com plex s pecif ic heat

𝑐𝑐 𝑃𝑃 ′

Real p art o f the com plex s pecif ic he at

𝑐𝑐 𝑃𝑃 ′′

Imagin ar y part of t he co mp lex sp ecifi c heat

𝐶𝐶 ∗ ( 𝜔𝜔 )

Complex cap acit ance of t h e cap acito r fil led w ith the m ateri al

U

R

Real pa rt of the comple x differ ential voltage

T

Temper atur e

T Colh - Is o
Phase transition temperature from he x a gonal c ol umnar mesophase to

isotropic phase

158

T Cry - Colh
Phase transition temp erat ure fro m pl asti c cr ystall ine p hase t o

hexagonal c ol umnar mes ophase
C

s

Heat c apaci t y of the s am p le

T

g
th erm a l

Ther mal gla ss transition te mperature

T

g
dy namic

Dy n amic gla ss transition temp erature

T 0

Voge l or ideal gla ss tr ansition temperatu re

Δ T g

Width of the glass tra nsition

Ṫ

Hea tin g/co oling rate

σ ∗

Complex conductivit y

σ ′

Real part of the complex conductivity

σ ′′

Imag i nar y part of the c o mplex conductivit y

σ 𝐷𝐷𝐶𝐶

Direct cu rrent co ndu ct ivi t y

Lis t of Cons tants
𝜀𝜀 0

Diele ctric permittivity constant in vac uum ( ε 0 = 8.854 10 - 12 A sV -1 m -1 )

R

Ideal gas constant (R = 8.314 J m ol -1 K -1 )

List of Peer- Re vie wed P ublic ation s
1. A. Yildir im , P. Sz ymoniak, K. Sentker, M. Butschies, A. Bühlme y e r, P. Huber, S. Lasc h at,
A. S chönhals, D y namic s and ionic conductivity of ionic liquid cr y st als forming a
hexagonal c ol umnar mes ophase. Phys.Chem.Chem.Phys . 2018 , 20, 5626 – 5635.
2. K. Sentker, A. W. Zantop, M. Lippmann, T. Hofmann, O. H. Se eck, A. V. Kit yk,
A. Yildirim , A. Schönhals, M . G. Mazza, P. Hub er, Quantized self - assem b l y of discot ic
rings in a liquid crysta l c onfined in nanopores, Phys. Rev. L ett . 2018 , 120, 067801.
3. A. Yildir im , K. Sentker, G. J . Smales, B. R. Pauw, P . Huber, A. Schönhals, Col lective
orientational order and phase behavior of a di scotic liquid cry stal un der nanosca l e
confinement. Nanoscale Adv. 2019 , 1, 1104–1116 .
4. A. Yildir im , A. Bühlmey er , S. Ha y a shi, J . C. Hae nle, K. Sentker, C. Krause, P. Huber, S.
La s chat, A. S chönhals, Multipl e gla s s y dyna mi cs in dipol e functionalized tripheny l ene-
based d is coti c liq uid cr y s t als rev eal ed b y broad b an d di elect ric spect ros co p y and ad v anced
calo rimetr y – Assessment of the molecu la r origin. Phys. Chem. Chem. Phys. 2019 , 21,
18265–18277.

159

5. K. Sentker, A. Y ildirim , M. Lippmann, A. W. Zantop, F. Be rtram, O. H. Seeck, M. G.
Mazza, T. Hofmann, A. V. Kity k, A. S chönhals, P. Huber, Self - a ssembly of liquid
crystals in nanoporoussolids for ada pti ve photonic metamater i als. The manuscript
submitted to N anoscale, 2019 .
6. A. Yildir im , K. Sentk er, C. Krause, P. Hub er, S. Laschat, A. Schönhals, Phase behavior
dyna m ics and conductivit y of triphen y l ene crown ether - based d isco tic l iq uid cr y s tal s. The
manuscript in preparation 2019 .

Lis t of Talk s
1. A. Yildir im , A. Bühlmeyer, S. Ha ya shi, J . C. Ha enle, K. Sentker, C. Krause, P. Huber, S.
La s chat, A. Schönhals , Mol ecular d ynamics of dipole func t ionalized tripheny l ene - bas ed
discotics, Spring Meetings, German Phy si cs Societ y (DPG) , Regensburg, Germany, 2019 .
2. A. Yildir im , P. Sz y moni ak, K. Sentker, P. Huber, A. Schönhals , Mol ecular m obilit y and
ionic conductivity of ionic liquid c r y stals forming a he x ag on al columna r me sophase, 10t h
Conference on Broadband Dielectric Spec tros copy and its Application , Brussles, Belgium,
2018 .
3. A. Yildir im . Liquid Crystals For m ing a Columnar Me s ophase: Structure, Dyna mi cs and
Elec tric Conductivity . Technische U niversität Berlin, Berlin, German y, 2018 .
4. A. Yildir im , P. Sz y moni ak, K. Sentker, M. Butschies, A. Bühlme y e r, P. Huber, S. Lascha t ,
A. Schönhals , Mol ecular mobility and ionic c ond uctivity o f ionic liquid cry s tals for min g a
hexagonal c ol umna r m esop hase, Spring Meetings, German Physics Society (DPG) , Be rli n,
German y , 2018 .
5. A. Yildir im , K. Sentke r, P. Huber, A. S chönhals , structure, d y namics and phase behavior
of a discotic liquid c r y st al confined in nanoporous anodic aluminum o x ide membran es,
Spring Meetings, German Physics Society (DPG) , D resden , G erman y , 201 7
6. A. Schönhals, A. Yildir im , C. Krause , Dielectric relaxation of discotic liquid c rystals , 16 th
International Symposium on Electretes , Le uv en, Belgium, 2017 .
7. A. Yildir im . Struct ure , d ynami cs and phase behavior of bulk and confined liquid cry stals,
Unive rsität Stuttgart , Stu ttga rt, Germany, 2017 .

160

List of Posters
1. A. Yildir im , P. Sz ymoniak, K. Sentke r, M. Butschies, A. Bühlme y e r, P. Huber, S. Laschat,
A. Schönhals , Molecular dyna m ics of dipole functi onalized tripheny l ene - based dis coti cs ,
10th Conference on Broadband Dielectric Spectroscopy and its Application , Brussles,
Belgium, 2018 .
2. A. Yildir im , K. Sentker, P. Huber, A . S chönhals, Colle c tive orientational order a nd phase
behavior of a dis cotic liquid cry s tal under confinement, 10th Conference on Broadband
Dielectric Spectroscopy and its Application , Brussles, Belgium, 2018 .
3. A. Yildir im , K. Sentker, P. Huber, A . S chönhals, Colle ctive orientational orde r and phase
behavior of a discotic liq uid cr y st al under confinem ent, Spring Meetings, German Physics
Soci ety (DPG ) , Berlin, German y , 2018 .
4. A. Yildir im , K. Sentker, P. Huber, A. Schönhals, Structure, dy n amics and phase behavior
of a discotic liquid cry sta l confined in nanoporous anodic a lum inum oxide membrane s, 9 th
International Conference on Porous Me di a & A nnual Meeting , Rotterdam, The
Netherlands, 2017 .
5. A. Yildir im , K. Sentker, P. Huber, A. Schönhals, Structure, dy n am ics and ph ase behav i or
of a discotic liquid cr y st al confined in nanoporous anodic aluminum ox ide membra n es,
10 th Liquid Matter Confere nce , Ljubljana, Slovenia, 2017 .
6. K. Sentker, A. Yildirim , A. W. Zantop, M. L ipp mann, T. Hofmann, O. H. Seec k, A. V.
Kityk, M. G. Mazza, A. Schönhals, P. Huber , Chara ct erization of the thermotropic phase
behavior and microscopic structure of a confined discotic liqui d crystal , 10 th L iquid Matter
Con feren ce , Ljubljana, Sl ovenia, 2017 .
7. K. Sentker, A. Yildirim , M. Lippmann, T. Ho fm ann, O. H. Seeck, A. V. Kit yk, A.
Schönhals, P. Huber , Fabric ation of orga nic nanowire s b y melt infiltra tion of a disco tic
liquid crystal: A combined X - ra y diffraction and optical birefrin ge nc e st udy , Spring
Meetin gs, Germa n Ph ysi cs Societ y (D PG ) , Dres d en, Germ an y, 2017
8. A. Yildir im , K. Sentk er, A. V. Kit yk , P. Huber, A . Schönhals , S tr uctu re an d d y n am ics o f
2,3,6,7,10,11- hexakis[hex y lox y ] t riphen y len e in nanoporous anodic a l umi num oxide
memb ranes , 10th Confer ence on Broadband Diel ectric Spectroscopy and i ts Application ,
Pi sa, Ital y, 2016 .

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