polyme s
A icle
Polye he Single and Double C ys alline Blends and he E ec
o Li hium Sal on Thei C ys allini y and Ionic Conduc i i y
Jo ge L. Olmedo-Ma ínez 1,† , Michele Pas o io 2,† , Elena Gabi ondo 1, Alessand a Lo enze i 2,
Ha i z Sa don 1, Da id Mece eyes 1,3 and Alejand o J. Mülle 1,3,*
Ci a ion: Olmedo-Ma ínez, J.L.;
Pas o io, M.; Gabi ondo, E.;
Lo enze i, A.; Sa don, H.;
Mece eyes, D.; Mülle , A.J. Polye he
Single and Double C ys alline Blends
and he E ec o Li hium Sal on Thei
C ys allini y and Ionic Conduc i i y.
Polyme s 2021,13, 2097. h ps://
doi.o g/10.3390/polym13132097
Academic Edi o s: I an Chodák and
Eamo M. Woo
Recei ed: 7 June 2021
Accep ed: 22 June 2021
Published: 25 June 2021
Publishe ’s No e: MDPI s ays neu al
wi h ega d o ju isdic ional claims in
published maps and ins i u ional a il-
ia ions.
Copy igh : © 2021 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
1POLYMAT and Depa men o Polyme s and Ad anced Ma e ials: Physics, Chemis y and Technology,
Facul y o Chemis y, Uni e si y o he Basque Coun y UPV/EHU, Paseo Manuel de La dizabal 3,
20018 Donos ia-San Sebas ián, Spain; [email p o ec ed] (J.L.O.-M.);
[email p o ec ed] (E.G.); ha i z.sa [email p o ec ed] (H.S.); [email p o ec ed] (D.M.)
2Depa men o Indus ial Enginee ing, Uni e si y o Pado a, ia Ma zolo, 9, 35131 Pado a, I aly;
[email p o ec ed] (M.P.); alessand a.lo [email p o ec ed] (A.L.)
3IKERBASQUE, Basque Founda ion o Science, 48009 Bilbao, Spain
*Co espondence: alejand [email p o ec ed]; Tel.: +34-943018191
† These au ho s con ibu ed equally o his wo k.
Abs ac :
In his wo k, blends o Poly(e hylene oxide), PEO, and poly(1,6-hexanediol), PHD, we e
p epa ed in a wide composi ion ange. They we e examined by Di e en ial Scanning Calo ime y
(DSC), Pola ized Ligh Op ical Mic oscopy (PLOM) and Wide Angle X- ay Sca e ing (WAXS). Based
on he esul s ob ained, he blends we e pa ially miscible in he mel and hei c ys alliza ion was
a unc ion o miscibili y and composi ion. C ys alliza ion igge ed phase sepa a ion. In blends
wi h highe PEO con en s bo h phases we e able o c ys allize due o he limi ed miscibili y in
his composi ion ange. On he o he hand, he blends wi h highe PHD con en s display highe
miscibili y and he e o e, only he PHD phase could c ys allize in hem. A nuclea ion e ec o
he PHD phase on he PEO phase was de ec ed, p obably caused by a ans e ence o impu i ies
mechanism. Since PEO is widely used as elec oly e in li hium ba e ies, he PEO/PHD blends
we e s udied wi h li hium bis( i luo ome hanesul onyl) imide (LiTFSI), and he e ec o Li-sal
concen a ion was s udied. We ound ha he li hium sal p e e en ially dissol es in he PEO phase
wi hou signi ican ly a ec ing he PHD componen . While he Li-sal educed he sphe uli e g ow h
a e o he PEO phase wi hin he blends, he o e all c ys alliza ion a e was enhanced because o he
s ong nuclea ing e ec o he PHD componen . The ionic conduc i i y was also de e mined o he
blends wi h Li-sal . A high empe a u es (>70
◦
C), he conduc i i y is in he o de o
~10−3S cm−1
,
and as he empe a u e dec eases, he c ys alliza ion o PHD was de ec ed. This imp o ed he
sel -s anding cha ac e o he blend ilms a high empe a u es as compa ed o he one o nea PEO.
Keywo ds: polye he s; PEO blends; ionic conduc i i y; iso he mal c ys alliza ion a e
1. In oduc ion
Alipha ic polye he s a e a b oad class o polyme s, nowadays used in a wide ange
o ields [
1
]. Howe e , hei indus ial applica ions a e limi ed o sho -chain alipha ic
polye he s. Comme cially a ailable sho chain alipha ic polye he s such as polye hylene
oxide (PEO), polyp opylene oxide (PPO) o poly e ahyd o u an (PTHF) a e indus ially ob-
ained by ing-opening polyme iza ion [
2
–
4
]. Recen ly, a sus ainable ou e o he syn hesis
o medium- o long-chain alipha ic polye he s has been epo ed [
5
]. This syn he ic me hod
open he possibili y o uning he leng h o he alipha ic chain o polye he s, p epa ing
di e en copolyme s and ine uning o hei Tmand c ys allini y [5–7].
One o he ac ual applica ions o PEO is as solid polyme elec oly es (SPEs) o li hium
ba e ies o elec ic ehicles [
8
]. Polye hylene oxide (PEO) s ands ou as he main hos poly-
me o polyme elec oly es, due o i s excellen capabili y o dissol e li hium sal s, and be-
cause i exhibi s high ionic conduc i i y alues a ela i e high empe a u es (>70
◦
C)
[9–11]
.
Polyme s 2021,13, 2097. h ps://doi.o g/10.3390/polym13132097 h ps://www.mdpi.com/jou nal/polyme s
Polyme s 2021,13, 2097 2 o 14
In pa icula , he polye hylene oxide (PEO)/li hium bis( i luo ome hanesul onyl) imide
(LiTFSI) sys em has been widely s udied because o he high dissocia ion and plas icizing
abili ies o LiTFSI, ha lead o be e ionic conduc i i ies compa ed o o he sal s [
12
,
13
].
Howe e , he high c ys allini y and he low mechanical s eng h o PEO a e s ill issues o
be imp o ed [
14
]. Speci ically, he c ys alliza ion limi s he ionic conduc i i y, due o he e-
duc ion o amo phous conduc i i y pa hways caused by he sphe uli ic g ow h [
15
]. Many
s a egies ha e been a emp ed o imp o e he comp ehensi e pe o mance o PEO-based
elec oly es, such as: ille addi ion (e.g., nanopa icles [
16
,
17
]), syn hesis o PEO copoly-
me s ( andom, block [
18
] o g a [
19
]), c osslinking [
20
] o blending echniques [
14
,
21
,
22
].
In pa icula , blending can supp ess c ys alliza ion, inc easing he pe cen age o he amo -
phous phase and as a esul he ionic conduc i i ies o polyme elec oly es a e imp o ed.
Compa ed o copolyme iza ion o PEO, polyme blending echnique is con enien , e i-
cien , and low cos . Indeed, he main ad an ages o polyme elec oly es p epa ed ia
blending me hod a e he simplici y o p epa a ion and easy con ol o physical p ope ies
by composi ional change, o e coming he se ious d awback o p epa ing elec oly es by
non i ial syn hesis me hods, which a e no e y sui able o p ac ical applica ions.
Fo his eason, di e en polyme blends ha e been s udied o imp o e a speci ic
p ope y, o example, polyca bona es and polyes e s [
21
–
23
], due hei high anodic s abili y.
Recen ly, Gao e al. epo ed a sys em polye he (PEO)/poly(e he -ace al) (poly (1,3,6-
ioxocane)) wi h LiTFSI; hey showed ha hese polyme s a e miscible and, depending on
he amoun o LiTFSI in he blend, i is possible o ob ain immiscible o miscible blends
when a c i ical alue is exceeded [
24
]. When ob aining comple ely miscible blends, he
cha ge anspo is a o ed.
P e iously in ou esea ch g oup i was ound ha LiTFSI ac s as a dilu ing agen
o polye he s [
25
]. This is o cou se good o he imp o emen o he ionic conduc i i y,
bu i can comp omise he mechanical p ope ies o PEO due o he loss o c ys allini y
and sel -s anding cha ac e . In his a icle, a e na y PEO/PHD/LiTFSI sys em is s udied,
since bo h polyme s p esen ionic conduc i i y when LiTFSI is added [
25
]. The goal o his
a icle is o in es iga e he polye he blending and he ionic conduc i i y and i s e ec on
he c ys allini y o he indi idual homopolyme s.
2. Ma e ials and Me hods
1,6-hexanediol (99%) was pu chased om Sigma-Ald ich (Mad id, Spain) and was
d ied in oluene be o e using i . Me hanesul onic acid (MSA, 99%), 1,5,7- iazabicyclo
[4.4.0] dec-5-ene (TBD, 98%), chlo o o m (CDCl
3
) and he es o he sol en s used in
his wo k we e supplied by Sigma-Ald ich and used as ecei ed. Poly(e hylene ox-
ide) (PEO, M
100 kg mol
−1
, powde ) was pu chased om Sigma-Ald ich. Finally, he
li hium bis( i luo ome hanesul onyl)imide (LiTFSI) (99.9%) sal was supplied by Sol ionic
(Toulouse, F ance).
2.1. Syn hesis o PHD: Bulk Sel -Condensa ion o 1,6-Hexanediol
In a 250 mL ound bo om lask 0.61 g o MSA and 0.25 g o TBD we e weighed
and hea ed a 90
◦
C o 30 min unde igo ous s i ing. Once he p o ic ionic sal was
p epa ed, 20 g o 1,6-hexanediol we e added o he lask and i was hea ed up o 130
◦
C
o 24 h unde acuum. The empe a u e was inc eased o 150
◦
C o he nex 24 h and
hen o 180
◦
C o he las 24 h. A e 72 h he eac ion was s opped by cooling i down
a oom empe a u e. Fo he pu i ica ion, he ma e ial was dissol ed in chlo o o m and
p ecipi a ed in cold me hanol. The esul ing polyme was il e ed and d ied i he o en
unde acuum a
40 ◦C
, o e nigh . The
1
H-NMR spec um o he ob ained polyme and
he calcula ion o he molecula weigh a e p esen ed in he Supplemen a y In o ma ion (S.
I.), Figu es S1 and S2.
Polyme s 2021,13, 2097 3 o 14
2.2. Blends P epa a ion
Blends be ween PEO and PHD we e p epa ed by a simple sol en e apo a ion me hod
(Scheme 1). E en when bo h polyme s a e soluble in chlo o o m, PEO ( ha ends o agg e-
ga e) is sligh ly less soluble han PHD, so i is added li le by li le unde s i ing. A se ies o
0.5 g samples was p epa ed wi h di e en weigh pe cen o PEO/PHD: 80/20 (
0.4 g/0.1 g
,
16 mL o CHCl
3
), 60/40 (0.3 g/0.2 g, 14 mL o CHCl
3
), 50/50 (0.25 g/0.25 g, 12 mL o
CHCl3), 40/60 (0.2 g/0.3 g, 12 mL o CHCl3) and 20/80 (0.1 g/0.4 g, 10 mL o CHCl3).
Scheme 1. Chemical s uc u e o he alipha ic polye he s used in his wo k.
The p epa a ion o PEO/PHD blends wi h LiTFSI sal equi ed some ex a wo k.
LiTFSI is indeed soluble in ace one o ace oni ile, bu no in chlo o o m. On he o he hand,
he opposi e is ue o PHD, while PEO is soluble bo h in chlo o o m and ace oni ile (mo e
easily in he la e ). So, he blends wi h sal we e dissol ed in an ace oni ile/chlo o o m
mix u e, wi h a ol/ ol% oughly equal o he one o he PEO/PHD in he blend. The
PHD- ich blends wi h sal could be success ully dissol ed also in a chlo o o m/ace one
(90/10 ol%) mix u e. I is wo h speci ying ha he w % o LiTFSI is e e ed o he inal
o al weigh o he sample (Li sal included).
2.3. Cha ac e iza ion
A di e en ial scanning calo ime e (Pe kin Elme DSC 8000, Mad id, Spain) equipped
wi h an In acoole II was employed o in es iga e he he mal beha io o he samples.
Indium and in s anda ds we e used o calib a e he equipmen . Fo he non-iso he mal
scans, samples we e i s hea ed wi h a scan a e o 20
◦
C min
−1
, om 25 o 100
◦
C,
and kep o 3 min a 100
◦
C o e ase he mal his o y. Then, hey we e cooled down
a 20
◦
C min
−1
o
−
70
◦
C and subsequen ly hea ed a 20
◦
C min
−1
a 100
◦
C. Samples
be ween 5 and 10 mg we e used (wi h highe weigh s o lowe cooling a es), placing
hem in sealed aluminum pans. Rega ding he iso he mal DSC expe imen s, he minimum
c ys alliza ion empe a u e (T
c, min
) was i s de e mined o each sample, ollowing he
p ocedu e ecommended by Lo enzo e al. [
26
]. This empe a u e ep esen s he minimum
one ha a oids he c ys alliza ion du ing he cooling s ep. So, once he s a ing
Tc,min
is
ixed, he iso he mal
Tc
ange is de ined by he o he 10 empe a u es in he (
Tc,min + 5 ◦C
)
ange, wi h 0.5
◦
C s eps. The e o e, he samples we e subjec ed o: hea ing om 25 o
100 ◦C
a 20
◦
C min
−1
; iso he mal holding a 100
◦
C o 3 min; cooling down o he selec ed
Tc
a 60
◦
C min
−1
; iso he mal holding a ha
Tc
un il he c ys alliza ion p ocess is sa u a ed;
and hea ing om he selec ed
Tc
o 100
◦
C a 20
◦
C min
−1
, in o de o egis e he mel ing
beha io a e he iso he mal measu emen .
X- ay powde di ac ion pa e ns we e collec ed by using a Philips X’pe PRO
au oma ic di ac ome e (Mad id, Spain) ope a ing a 40 kV and 40 mA, in he a- he a
con igu a ion, seconda y monoch oma o wi h Cu-K
α
adia ion (
λ
= 1.5418 Å) and a
PIXcel solid s a e de ec o (ac i e leng h in 2
θ
3.347
◦
). Da a we e collec ed om 5 o 70
◦
2
θ
(s ep size = 0.026 and ime pe s ep = 60 s) a oom empe a u e. A 1
◦
ixed solle
sli and di e gence sli gi ing a cons an olume o sample illumina ion we e used. The
blends we e hea ea ed p io o X- ay measu emen , all samples we e hea ed o 100
◦
C a
20 ◦C min−1
and cooled o oom empe a u e also a 20
◦
C min
−1
, so ha he condi ions
we e he same as in he DSC.
Sphe uli es nuclea ion and g ow h we e obse ed h ough a pola ized ligh op ical
mic oscope (Olympus BX51, Mad id, Spain), equipped wi h an Olympus SC50 digi al cam-
Polyme s 2021,13, 2097 4 o 14
e a (Mad id, Spain), wi h a Linkam-15 TP-91 ho s age (Epsom, England) and coupled o a
liquid ni ogen cooling sys em. Films o hickness oughly equal o 100
µ
m we e p epa ed
by mel ing he samples be ween wo glass slides. The expe imen al condi ions we e e y
simila o hose employed du ing he DSC iso he mal measu emen s. The samples we e
hea ed un il 30
◦
C abo e hei mel ing poin in o de o e ase hei he mal his o y, and hen
apidly cooled down om he mel o he selec ed iso he mal c ys alliza ion empe a u e,
Tc
, a 50
◦
C min
−1
. Finally, he samples we e kep a he
Tc
o he ime needed o le
he sphe uli es appea and o measu e he sphe uli ic g ow h a e. This p ocedu e was
epea ed a 10 di e en Tc.
Ionic conduc i i ies we e measu ed by elec ochemical impedance spec oscopy (EIS)
in an Au olab 302N po en ios a gal anos a (Me ohm AG, He isau, Swi ze land), wi h
he empe a u e con olled by a Mic ocell HC s a ion. The samples we e closed be ween
wo s ainless s eel elec odes (su ace a ea = 0.5 cm
2
). The plo s we e ob ained applying a
10 mV pe u ba ion o open ci cui po en ial in he equency ange o 100 kHz o 1 Hz.
3. Resul s and Discussion
3.1. Non-Iso he mal DSC o PEO/PHD Blends
PEO/PHD blends we e s udied in he whole composi ion ange o explo e hei
miscibili y and c ys alliza ion beha io . One o he i s clues ha indica e miscibili y
be ween wo polyme s is he appea ance o a single glass ansi ion empe a u e (T
g
).
Howe e , in his case, bo h polyme s show low T
g
(e.g., PEO
≈ −
60
◦
C [
27
]) and a e
highly c ys alline. Fo his eason, de e mining hei T
g
by DSC is di icul , as he change
in speci ic hea is oo small. Ne e heless, he DSC can p o ide aluable in o ma ion ia
he c ys alliza ion and mel ing o he samples.
The non-iso he mal DSC uns we e ca ied ou a 20
◦
C min
−1
. In Figu e 1, he
expe imen al cu es ha e been supe imposed o scans ha we e deno ed “ heo e ical”.
They we e calcula ed om he expe imen al DSC scans o he nea homopolyme s, hey
we e mul iplied by hei weigh ac ion in he blends and hen added. In his way, hese
heo e ical cu es gi e an idea o how he DSC aces should appea when he e is no
in e ac ion wha soe e be ween he blend componen s.
The p esence o a double peak in Figu e 1indica es ha phase sepa a ion akes place,
while he p esence o a single peak in he middle o he nea polyme s could in p inciple
indica e a single c ys alline phase. Focusing on he nea componen s, he T
m
o PEO is
highe han ha o he PHD, while he opposi e si ua ion is obse ed in hei c ys alliza ion
empe a u es. This is a esul o di e en he e ogenei y con en s, as his pa ame e can
in luence he T
c
. On he o he hand, T
m
is p opo ional o he lamella hickness o he
c ys alline phase (and chemical s uc u e) [
28
] ha is o med, while T
c
depends on chemical
s uc u e and nuclea ion densi y.
Figu e 1a shows he DSC cooling scans om he mel and Figu e 1b he subsequen
second hea ing scans. WAXS expe imen s o he same samples a e cooling om he
mel a 20
◦
C min
−1
can be obse ed in Figu e 2and will be discussed below. Acco ding
o Figu e 2, in he PEO/PHD blends ha a e ich in PHD, i.e., 20/80 and 40/60, he only
componen capable o c ys alliza ion is he PHD. This is in e es ing as i demons a es ha
when he blends con ain a majo i y o PHD he c ys alliza ion o he PEO phase is hinde ed
and his can be in e p e ed as a sign o blend miscibili y. The 20/80 PEO/PHD blend
exhibi s wo c ys alliza ion peaks du ing cooling om he mel ha acco ding o WAXS a e
bo h due o PHD c ys als. This is an uncommon beha io as ac iona ed c ys alliza ion
is no mally associa ed wi h he mino componen in blends [
29
]. The e o e, his peculia
beha io me i s u u e s udies ha a e ou side he scope o he p esen con ibu ion.
Polyme s 2021,13, 2097 5 o 14
Figu e 1.
PEO/PHD blends: (
a
) DSC cooling scans a 20
◦
C min
−1
and (
b
) DSC second hea ing scans
a 20 ◦C min−1.
Polyme s 2021,13, 2097 6 o 14
Figu e 2.
WAXS di ac og ams o PEO/PHD blends. (
a
) Nea PEO, (
b
) 80/20 PEO/PHD, (
c
) 60/40
PEO/PHD, (d) 50/50 PEO/PHD, (e) 40/60 PEO/PHD, ( ) 20/80 PEO/PHD, (g) Nea PHD.
The blends wi h PEO con en s o 50 w % and highe a e all double c ys alline blends
as demons a ed by WAXS in Figu e 2. This means ha wo c ys alline phases a e o med
and acco ding o Figu e 2, he c ys alline s uc u e does no change wi h blend composi ion
( he e a e no changes in he WAXS e lec ions). This means ha once c ys alliza ion
s a s, phase sepa a ion is igge ed and wi hin each c ys alline phase, he second blend
componen is comple ely excluded om he c ys als o he componen ha is c ys allizing.
The e is a clea nuclea ing e ec o PHD on he PEO phase, as he c ys alliza ion peak
o PEO shi s o highe empe a u es. This nuclea ion e ec is esponsible o he o e lap
o bo h c ys alliza ion peaks o he 50/50 PEO/PHD in o a single peak. The mel ing o his
50/50 blend occu s displaying a single endo he mic peak a empe a u es sligh ly highe
han he mel ing peak o nea PHD, bu we know by WAXS (Figu e 2) ha bo h phases
c ys allize sepa a ely ( hey do no sha e he same c ys al la ice). Hence, he single mel ing
peak in Figu e 1b co esponding o he 50/50 PEO/PHD is due o a coinciden mel ing
p ocess o bo h c ys alline phases.
Fo he 80/20 PEO/PHD blend, he la ges c ys alliza ion peak in Figu e 1a (which
should co espond o he PEO phase) is clea ly shi ed owa ds highe empe a u es. This
may sugges ha he PHD mino phase ac s as a nuclea ing agen o he main phase (PEO).
Since he e ogeneous nuclea ion akes place on a solid phase, his could be due o a ans e
o impu i ies (e.g., polyme iza ion ca alys ) p esen in he PHD phase o he PEO phase.
This has al eady been demons a ed o o he blends (e.g., iPP/PS blends [
30
]). The ac
ha PHD (e en in he mol en s a e) ac s as a nuclea ing agen o PEO is unusual, bu
a simila beha io has al eady been epo ed o o he sys ems in which an amo phous
polyme ac s as a nuclea ing agen o a semi-c ys alline polyme , o example, a ac ic
polys y ene o polyp opylene [
31
], o poly( inyl bu y al) o poly(bu ylene succina e) [
32
].
Bo h PEO ich blends, i.e., 80/20 and 60/40 PEO/PHD, exhibi clea double endo he -
mic peaks in Figu e 1b co esponding o he mel ing o he PHD c ys alline phase and he
PEO c ys alline phase. The di e ences be ween he heo e ical and expe imen al blends
indica e ha he blends a e a leas pa ially miscible wi h mos p obably an asymme ical
phase diag am, whose p ecise de e mina ion is ou side he scope o he p esen wo k.
Polyme s 2021,13, 2097 7 o 14
Clea ly, he miscibili y is highe o he blends wi h la ge con en s o PHD and limi ed o
blends wi h highe PEO con en s.
3.2. Wide Angle X- ay Sca e ing o PEO/PHD Blends
The WAXS s udy was ca ied ou o he blends o de e mine i he e a e any changes
in he c ys al s uc u e o he nea polyme s when mixed. In Figu e 2, he di ac ion
pa e ns o he polyme s and blends a 25
◦
C a e p esen ed. The samples we e i s hea ed
o he mel and hen cooled a 20
◦
C min
−1
o ep oduce simila condi ions o he samples
in Figu e 1a.
The e lec ions o nea PEO a e obse ed a 19.4
◦
and 23.45
◦
, which a e assigned o he
(120) and (112) planes, espec i ely [
33
–
35
], and he e lec ions o nea PHD a e p esen ed
a 19.85
◦
and 24.29
◦
, and a e assigned o he (020) and (110) planes, espec i ely [
36
,
37
].
The blends 80/20, 60/40, 50/50 PEO/PHD show he peaks o bo h c ys alline s uc u es
wi hou any changes in he 2
θ
angles, which indica es he wo phases c ys allize sepa a ely
and wi hou any modi ica ion o he c ys alline s uc u e o he nea blend componen s.
On he o he hand, in he 40/60 and 20/80 PEO/PHD blends, only he cha ac e is ic
e lec ions o PHD a e p esen ed, which sugges s ha he p esence o PHD p e en s he
c ys alliza ion o PEO in he blends, possibly because he blends exhibi miscibili y in he
mel s a e.
3.3. Mo phology and C ys al G ow h Ra e
The mo phology and sphe uli ic g ow h a e we e analyzed by pola ized ligh op ical
mic oscopy (PLOM). Wi h his echnique i is possible o measu e he iso he mal g ow h
o sphe uli es om he mel in samples ha do no ha e a e y la ge nuclea ion densi y.
Figu e 3a,b show ha PEO o ms la ge sphe uli es, while PHD o ms small axiali es wi h
high nuclea ion densi y. The supe s uc u es g ow h a e (e.g., sphe uli es o axiali es)
depends on a compe i ion be ween seconda y nuclea ion and di usion [38,39].
Figu e 3.
PLOM mic og aphs ob ained du ing iso he mal c ys alliza ion a 40
◦
C. (
a
) PEO, (
b
) PHD, (
c
) 80/20 PEO/PHD
blend, (d) 50/50 PEO/PHD blend, and (e) 20/80 PEO/PHD.
Figu e 3shows he PLOM images o he nea homopolyme s and h ee di e en
composi ions, ob ained a 40
◦
C. Nea PEO p esen s as expec ed la ge nega i e sphe uli es
(Figu e 3a), while PHD c ys allizes in small axiali es (Figu e 3b). The composi ion 80/20
PEO/PHD (Figu e 3c), shows a la ge numbe o he PEO phase sphe uli es as compa ed
wi h nea PEO, con i ming he nuclea ion e ec o PHD addi ion epo ed in Figu e 1a.
The p esence o e y small PHD phase axiali es can also be obse ed. Figu e 3d p esen s
he mo phology o he 50/50 PEO/PHD blend, whe e PEO phase la ge sphe uli es can
be clea ly seen. Some small PHD phase axiali es a e also obse ed, indica ing ha bo h
phases can c ys allize. These esul s o he 80/20 and 50/50 PEO/PHD blends show ha
Polyme s 2021,13, 2097 8 o 14
bo h componen s a e able o c ys allize unde iso he mal condi ions and a e consis en
wi h DSC and WAXS esul s aken a e non-iso he mal c ys alliza ion.
Finally, o he 20/80 PEO/PHD blend, Figu e 3e shows ha al hough mos o he
op ical iew ield is illed wi h PHD phase axiali es, he e a e some la ge bi e ingen s uc-
u es ha a e p obably cons i u ed by he PEO phase. This is an unexpec ed obse a ion,
as in Figu es 1and 2, his sample unde non-iso he mal condi ions has a di e en beha io ,
as only he PHD phase is able o c ys allize. Appa en ly, unde iso he mal condi ions, and
gi en enough ime, bo h phases can e en ually c ys allize. Ne e heless, as he majo i y o
he sample c ys allizes wi h e y small PHD phase axiali es, g ow h a e measu emen s
p o ed o be impossible.
The sphe uli ic g ow h a e measu emen s we e possible only o nea PEO and he
PEO- ich composi ions (80/20 and 50/50 PEO/PHD) bu no o he es o he samples, as
hei nuclea ion densi y was oo high.
Figu e 4shows he sphe uli ic g ow h a e as a unc ion o empe a u e and he solid
lines a e i s o he Lau i zen and Ho man heo y [
40
,
41
], see also he S.I. The sphe uli ic
g ow h a e o he 80/20 PEO/PHD blend ma ches pe ec ly wi h ha o nea PEO, a esul
ha indica es immiscibili y be ween he wo componen s o his composi ion. This esul
is in line wi h he DSC mel ing cu es o Figu e 1b ha show a simila beha io be ween
he expe imen al and he heo e ical immiscible blend DSC hea ing scans.
Figu e 4.
Sphe uli ic g ow h a e (G) as a unc ion o iso he mal c ys alliza ion empe a u e o nea
PEO and o he PEO componen o he 80/20 and 50/50 PEO/PHD blends.
On he o he hand, Figu e 4also shows he sphe uli ic g ow h a e e sus empe a u e
o he 50/50 PEO/PHD blend, whe e a clea dec ease in he PEO phase g ow h a e is
obse ed wi h espec o nea PEO. This esul can be aken as an e idence o miscibili y
be ween PEO and PHD componen s, because i hey we e immiscible, no change in he
PEO sphe uli es g ow h a e would be expec ed.
3.4. Non-Iso he mal DSC o PEO/PHD Blends wi h LiTFSI
LiTFSI sal was added o he 80/20 PEO/PHD blend o e alua e he e ec o his sal
on he c ys alliza ion. In p e ious wo k, we demons a ed ha LiTFSI ac s as a diluen
agen ha dep esses he T
m
in hese polye he s [
25
] (Figu es S3 and S4). Figu e 5a shows
Polyme s 2021,13, 2097 9 o 14
cooling scans om he mel o he 80/20 PEO/PHD blend wi h di e en concen a ions o
LiTFSI (10, 20 and 30 w % LiTFSI).
Figu e 5.
DSC o he PEO/PHD blends: (
a
) du ing cooling om he mel , (
b
) subsequen mel ing scans, (
c
) change in T
m
o he PEO and PHD homopolyme s as a unc ion o LiTFSI concen a ion, (
d
) change in T
m
o he PEO and PHD phases
wi hin he 80/20 PEO/PHD as a unc ion o LiTFSI concen a ion.
In he 80/20 PEO/PHD blend wi hou sal , one main c ys alliza ion peak is obse ed,
which esul s om he c ys alliza ion o he PEO phase. I is also possible o obse e a
low empe a u e shoulde ha co esponds o he c ys alliza ion o he PHD phase. Upon
sal addi ion, he T
c
o he PEO phase dec eases as a unc ion o he LiTFSI concen a ion
(see he a ow ha guides he eye in Figu e 5a), whe eas he T
c
o he PHD phase emains
cons an (app ox. a 40
◦
C, see he dashed e ical line in Figu e 5a). The same e ec
is obse ed in he usion beha iou shown du ing he second DSC hea ing scans (see
Figu e 5b
), whe e he T
m
alues o he PEO phase dec eases (see he a ow ha guides he
eye in Figu e 5b) while he T
m
alue o he PHD phase emains cons an a 58
◦
C (see he
e ical dashed line in Figu e 5b). The abo e desc ibed ends o T
m
as a unc ion o sal
con en can be clea ly obse ed in Figu e 5c,d, espec i ely.
The esul s shown in Figu e 5indica e ha he li hium sal p e e s o dissol e in
he PEO phase a he han in he PHD phase wi hin he 80/20 PEO/PHD blend. This is
also co obo a ed by he dec ease in he en halpies o c ys alliza ion and mel ing o he
PEO phase as he sal concen a ion inc eases, while hose o he PHD phase do no seem
o be al e ed (al hough he o e lapping o signals make his obse a ion di icul ). The
beha iou o his blend wi h li hium sal could be a good solu ion o he mechanical s abili y
p oblems ha hese ypes o elec oly es p esen o li hium ba e ies, as e en a high li hium
concen a ions, he PHD phase emains semi-c ys alline, while he PEO/li hium phase
becomes ully amo phous a 30% li hium loadings.
