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Full PaPe
Piezoelec ic Nylon-11 Fibe s o Elec onic Tex iles, Ene gy
Ha es ing and Sensing
Saleem Anwa , Mo eza Hassanpou Ami i, Shuai Jiang, Mohammad Mahdi Abolhasani,
Paulo R. F. Rocha, and Kamal Asadi*
Elec onic ex iles and unc ional ab ics a e among he key cons i uen s
en isioned o wea able elec onics applica ions. Fo e- ex iles, he challenge
is o p ocess ma e ials o desi ed elec onic p ope ies such as piezoelec-
ici y in o ibe s o be in eg a ed as we s o w aps in he ab ics. Nylons,
i s in oduced in he 1940s o s ockings, a e among he mos widely used
syn he ic ibe s in ex iles. Howe e , ealiza ion o nylon-based e- ex iles has
emained elusi e due o he di icul y o achie ing he piezoelec ic phase in
he nylon ibe s. He e, piezoelec ic nylon-11 ibe s a e demons a ed and i is
shown ha he esul ing ibe s a e iable o applica ions in ene gy ha es ing
om low equency mechanical ib a ions and in mo ion senso s. A simula-
ion s udy is p esen ed ha elucida es on he sensi i i y o he nylon-11 ibe s
owa d ex e nal mechanical s imuli. Mo eo e , a s a egy is p oposed and
alida ed o signi ican ly boos he elec ical pe o mance o he ibe s. Since
a la ge ac ion o he ex ile indus y is based on nylon ibe s, he demons a-
ion o piezoelec ic nylon ibe s will be a majo s ep owa d ealiza ion o
elec onic ex iles o applica ions in appa els, heal h moni o ing, spo swea ,
and po able ene gy gene a ion.
DOI: 10.1002/ad m.202004326
D . S. Anwa , M. Hassanpou Ami i, S. Jiang, D . M. M. Abolhasani,
P o . K. Asadi
Max-Planck Ins i u e o Polyme Resea ch
Acke mannweg 10, Mainz, Ge many
E-mail: [email p o ec ed]
D . S. Anwa
School o Chemical & Ma e ials Enginee ing
Na ional Uni e si y o Sciences & Technology
Sec o H-12, Islamabad, Pakis an
ha is needed o d i ing he elec onics
used in he same ab ic.[1,2,4] Piezoelec ic
polyme s a e ideal o ene gy ha es ing
in e- ex iles because o he omnip esence
o mechanical ib a ions o de o ma ions,
which can be con e ed in o elec ici y.[5]
Fu he mo e, such polyme s ha e ela-
i ely la ge piezoelec ic ol age coe i-
cien s, which ende s hem as he ideal
ma e ials o p essu e sensing[6–9] ideally
sui ed o applica ion in a i icial skins.
Rega dless o he en isioned applica ion,
he i s s ep owa d a piezoelec ic ab ic
is o ealize ibe s ha a e piezoelec ic.
Nylons (o polyamides) ibe s, in o-
duced in he 1940s’ o he i s ime in
s ockings, a e one o he mos success ul
syn he ic ibe s wi h a well-es ablished
ex ile indus y.[10,11] Wi hin he amily,
odd-nylons cons i u e he na u al choice
o ealiza ion o e- ex iles i c ys alized
in hei piezoelec ic phase. Fo ins ance,
nylon-11, he well-s udied odd-nylons, has
a ious c ys alline phases, namely α, α′, ϒ, and δ′ o which only
he δ′-phase shows s ong piezoelec ic ac i i y. The iclinic
α-phase (simila ly αʹ-phase) is s ongly hyd ogen bonded.[12,13]
Polyc ys alline ilms o α- o α′-phase nylon-11 do no show pie-
zoelec ici y due o andom pola i y o he c ys alline domains,
which canno be aligned by elec ic poling because he s ong
in e -chain hyd ogen bonding necessi a es applica ion o an
elec ic ield la ge han he b eakdown ield. The ϒ-phase is
© 2020 The Au ho s. Published by Wiley-VCH GmbH. This is an open
access a icle unde he e ms o he C ea i e Commons A ibu ion
License, which pe mi s use, dis ibu ion and ep oduc ion in any
medium, p o ided he o iginal wo k is p ope ly ci ed.
The ORCID iden i ica ion numbe (s) o he au ho (s) o his a icle
can be ound unde h ps://doi.o g/10.1002/ad m.202004326.
D . P. R. F. Rocha
Cen e o Biosenso s, Bioelec onics and Biode ices (C3Bio)
Depa men o Elec onic and Elec ical Enginee ing
Uni e si y o Ba h
Cla e on Down, Ba h BA2 7AY, UK
D . P. R. F. Rocha
Cen e o Func ional Ecology (CFE)
Depa men o Li e Sciences
Uni e si y o Coimb a
Coimb a 3000-456, Po ugal
P o . K. Asadi
Depa men o Physics
Uni e si y o Ba h
Cla e on Down, Ba h BA2 7AY, UK
E-mail: [email p o ec ed]
1. In oduc ion
Elec onic ex iles (o e- ex iles), a key echnology enable o
he eme ging a i icial skins and sma ga men s, seamlessly
in eg a e elec onic elemen s such as p essu e senso s, ac ua-
o s, and mic ocon olle s in a ab ic.[1–3] Tex iles ha gen-
e a e elec ici y om he en i onmen ha e been sugges ed
as a p omising eplacemen o ba e ies, o supply he powe
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only sligh ly pola , shows weak swi chable dipole and he e o e
has weak piezoelec ic ac i i y.[12] In con as , he δʹ-phase[12,14–22]
has a highly pola smec ic pseudohexagonal chain a angemen
wi h poo ly o ganized hyd ogen bonds be ween he chains.
The swi chabili y o he dipoles upon applica ion o an ex e nal
elec ic ield allows o poling o he δʹ-phase nylon-11 and o
achie e a s ong piezoelec ic ac i i y.[23,24]
E- ex iles based on piezoelec ic nylon-11 ha e ne e been
ealized because o he di icul ies in achie ing he piezoelec ic
δʹ-phase in nylon-11 ibe s. The con en ional ibe p oduc ion
me hods, mel ex usion and mel spinning, p oduce non-
piezoelec ic polyc ys alline α-phase nylon ibe s wi h a hick-
ness o ens o mic ome e .[10,13] Solu ion cas ing o nylon-11
om i luo oace ic acid (TFA) o ea ing he α-phase in
sodium hyd oxide sal solu ion[25] p oduces he ϒ-phase.[12]
Recen ly, a empla e we ing echnique has been employed o
p oduce nylon-11 nanowi es o ene gy ha es ing applica-
ions.[26] The nanowi es ypically exhibi a mix u e o α- and
ϒ-phases ins ead o he desi ed piezoelec ic δʹ-phase.[27] A sum-
ma y o he e y limi ed li e a u e on piezoelec ic pu ely nylon
ibe s is gi en in Table S1, Suppo ing In o ma ion. Clea ly,
only he weakly pola ϒ-phase nylon has been demons a ed
so a , which concomi an ly yields low ene gy ha es ing pe -
o mance wi h nea ly 30 nW cm−2. Fab ica ing con inuous and
mechanically obus elec ospun ibe s om m-c esol, o mic
acid, and i luo oace ic acid ( ypical sol en s used in p o-
cessing o nylon) is challenging because he esul ing ibe s a e
non-piezoelec ic α- o ϒ-phase. The e o e, i is no i ial o
achie e he piezoelec ic δ′-phase. In his ega ds, ab ica ion o
δʹ-phase nylon ibe s wi h s ong piezoelec ic esponse would
be a majo b eak h ough ha will pa e he way owa d ealiza-
ion o e- ex iles.
Fo nylon-11 mel s, he cooling a e de e mines he c ys al-
line s uc u e a oom empe a u e. I has been demons a ed
ha a e y as cooling o he mel leads o he piezoelec ic δ′-
phase, whe eas a slow cooling a o s he o ma ion o he non-
piezoelec ic phases.[28] I he e o e can be specula ed ha he
same δ′-phase can be achie ed o ibe s p ocessed om solu-
ion p o ided ha he sol en is apidly deple ed om he ibe .
To ha end, low boiling poin sol en s wi h high apo p es-
su e such as TFA a e ideal. Howe e , he p oblem is ha TFA
molecules may emain inside nylon, e en a e long exposu e
o high acuum (>10−3 mba ) due o he o ma ion o s ong
hyd ogen bond be ween he TFA molecules and he amide
moie ies on he nylon-11 chains. As a esul , as quench o he
sol en canno be ealized and he nylon-11 ibe s c ys alize in
a non-piezoelec ic c ys alline o m, ϒ-phase, ende ing he
nano ibe s imp ac ical o he en isioned applica ions.
He e, we demons a e δʹ-phase piezoelec ic nylon-11 ibe s,
o he i s ime o he bes o ou knowledge, by elec ospin-
ning om a ca e ully designed nylon-11 solu ion. We p opose
addi ion o ace one o nylon solu ion o acili a e as deple-
ion o sol en because ace one o ms a e y s ong hyd ogen
bond wi h bonding ene gy o nea ly −10kcal mol−1 wi h TFA.[29]
Because o he much s onge a ini y o he TFA molecules o
o m hyd ogen bond wi h ace one han wi h he amide moie-
ies on nylon chains, upon e apo a ion he ace one molecules
will ca y he TFA molecules ou o he polyme . Fas e apo a-
ion condi ions, which imi a es as quenching om he mel ,
yields he piezoelec ic phase in nylon-11 ibe .
The elec ospun nylon-11 ibe s a e sui able o ene gy ha -
es ing o o sensing applica ions because he ibe s a e
sel -poled and p oduce ol age upon mechanical ib a ion o
de o ma ion. Th ough p ocess op imiza ion, i is shown ha
nylon-11 nonwo en ab ic can e icien ly ha es he ene gy o
mechanical ib a ions and deli e a eal powe densi ies as high
as 3.1 µW cm−2, wo o de s o magni ude la ge han hose based
on ϒ-phase nylon ibe s. The nylon-11 nano ibe ma moun ed
on hand can also de ec sligh mo ions o he inge s and can
he e o e be applied as mo emen senso . A ini e elemen (FE)
simula ion s udy is p esen ed ha elucida es he ole o c ys al-
line phases and he ibe diame e on he piezoelec ic ac i i y.
Th ough FE-simula ions, i is subs an ia ed ha ealiza ion o
nylon-11 po ous ibe s, is a iable s a egy o signi ican ly boos
he elec ical pe o mance o he ibe s. The demons a ion o
piezoelec ic nylon ibe s wi h an ou lined s a egy o enhance he
piezoelec ic esponse will be a majo s ep owa d o ealiza ion
o sma and wea able elec onic ex iles o applica ions such as
in heal h moni o ing, spo swea and po able ene gy gene a ion.
2. Resul s and Discussion
2.1. Sol en Sys em
To e ec i ely emo e all he TFA molecules om he polyme ,
mix u es nea 1:1 TFA:ace one mole% a e needed. Th ee di -
e en TFA:ace one mix u es wi h 60:40, 50:50, and 40:60mol%
a e p epa ed. The mix u e wi h TFA:ace one 60:40 mol%
quickly dissol es nylon-11 a oom empe a u e. The 40:60mol%
TFA:ace one composi ion howe e does no dissol e nylon-11,
which we a ibu e o he deshielding o he p o on due o an
excessi e amoun o ace one. The 50:50 mix u e also dissol es
nylon-11. Howe e since he 50:50 mix u e is a he bo de o
solubili y, we ocus only on sol en composi ion 60:40 mol%
TFA:ace one. The boiling poin and apo p essu e o he sol-
en mix u e 60:40 mol% TFA:ace one amoun o 110 ± 2 °C
and 2.5 ± 0.5kPa.Figu e S1, Suppo ing In o ma ion shows 1H
NMR spec a o pu e TFA and TFA:ace one (60:40 mol%). The
p o on peak o TFA occu s a 12.47 pa s pe million (ppm).
Fo he TFA:ace one (60:40 mol%), he p o on peak shi s lin-
ea ly o a highe alue o 14.00ppm. In sha p con as , p o on
shi in nylon-11 solu ion in TFA amoun o only 12.58 ppm.
The shi in he p o on peak posi ion, clea ly indica es o ma-
ion o s onge hyd ogen bonds be ween TFA and ace one.
To con i m he e ec i eness o adding ace one in emo ing
TFA om nylon-11, wo nylon-11 ilms a e p epa ed by spin-
coa ing om 5 w % solu ion in TFA only and in mix u e o
TFA:ace one (60:40 mol%). Vacuum quenching echnique is
used o deple e he sol en .[22] As can be seen om Figu eS2,
Suppo ing In o ma ion, a huge dielec ic loss is obse ed
pa icula ly a low equencies o he nylon-11 ilm p ocessed
om TFA, which is due o he p esence o TFA anions inside
he ilm. In sha p con as , nylon hin- ilms p ocessed om
TFA:ace one (60:40 mol%) exhibi low dielec ic loss due o lack
o subs an ially educed numbe o ions. The e o e, addi ion
o ace one is an e ec i e way o subs an ially emo e TFA ions
om nylon-11 upon solu ion p ocessing. Fo he es o his
wo k TFA:ace one (60:40 mol%) is used as sol en unless i is
explici ly men ioned o he wise.
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2.2. Elec ospinning Op imiza ion
The schema ic o elec ospinning se up is shown in Figu eS3,
Suppo ing In o ma ion. Va ious pa ame e s a e a ied o
ind he op imized p ocess window in o de o achie e bead-
ee nano ibe s ha a e composed o δ′ piezoelec ic phase.
As s a ing poin , nylon-11 ibe s a e elec ospun om 10 w %
solu ion a 20 kV a a a e o 1 mL h−1. The esul ing ibe s,
Figu e S4, Suppo ing In o ma ion, show o ma ion o beads.
Subsequen ly a se ies o expe imen s a e pe o med h ough
which he elec ospinning pa ame e s a e a ied sys em-
a ically. A e he op imiza ion p ocess, de ails a e gi en in
Figu es S5–S7, Suppo ing In o ma ion, bead- ee ibe s a e
ob ained. Following he op imiza ion p ocess, he solu ion con-
cen a ion and he eed a es a e uned o p oduce ibe s wi h
ou di e en diame e s named he ea e NF1 o he hinnes
nano ibe o NF4 o he hickes one. A ypical scanning elec-
on mic oscope (SEM) images o andomly aligned bead- ee
nano ibe s wi h di e en diame e s a e gi en in Figu e 1a–d.
A summa y o he esul ing ibe diame e s o NF1 o NF4 is
gi en in Figu e1e. The diame e o he nylon-11 nano ibe s can
be accu a ely uned h ough solu ion concen a ion and eed
a e om 55 ± 10nm o NF1 o 1000 ± 300 o NF4.
To in es iga e whe he elec ospinning o ibe s om
TFA:ace one solu ion yield he piezoelec ic δʹ-phase o nylon-
11, X- ay di ac ion (XRD) ha e been pe o med. As he i s
s ep, wo e e ence XRD measu emen s a e pe o med on mel -
quenched-s e ched ilm (δˊ-phase), and he d op-cas ed ilm
om TFA solu ion (ϒ-phase), Figu e S8, Suppo ing In o ma-
ion. Fo he mel -quenched and subsequen ly s e ched (MQS)
ilm, he di ac ion peak is he sum o (100) and (010/110) e lec-
ions, which occu a an iden ical 2θ= 20.95° and a e e e ed
as he in e chain dis ance along he hyd ogen bonds and he
in e shee dis ance be ween he hyd ogen-bonded shee s,
espec i ely. The δʹ-phase shows he la ges la e al spacing o
0.424nm be ween he shee s, which is also esponsible o e -
oelec ici y in MQS samples o nylon-11.[30] Fo he ϒ-phase
e e ence ilm, howe e , he e a e wo clea ly dis inc peaks o
(100) and (010/110) e lec ions, which a e posi ioned a 2θ= 21°
and 21.3°, espec i ely. The d-spacings a e gi en in Table 1, Sup-
po ing In o ma ion. The peak posi ions o he e e ence sam-
ples a e aken as cue o he analysis o he nano ibe s.
The XRD di ac og ams o he nano ibe s a e gi en in
Figu e2. Fo he ibe s wi h hinnes diame e , ha is, NF1
and NF2, he XRD di ac og ams show a la ge b oad peak,
wi h a iny peak on he shoulde a 2θ= 24°. Appea ance o
a clea peak a 24° is due o he p esence o he αʹ-phase. The
co esponding d-spacing o (100) and (010/110) e lec ions, a e
decon olu ion, amoun s o 0.415 and 0.375 nm, espec i ely,
ma ching exac ly wi h he epo ed peaks o he αʹ-phase.[30,31]
Fo ma ion o he αʹ-phase is due o he be e o de o he
molecula chains a small ibe diame e s. The low iscosi y o
he nylon-11 solu ion combined wi h la ge po en ial g adien ,
o ce he nylon-11 chains o pack in a highly o de ed s uc-
u e. We no e ha all he di ac ion peaks o he nano ibe s
appea na owe han hose o he MQS ilms indica ing be e
alignmen o he polyme chains along he ibe di ec ion. As
he diame e o he nano ibe inc eases o 200 nm, NF3, he
decon olu ed (100) and (010/110) e lec ions, hold exac ly he
same posi ion as hose shown in he e e ence MQS ilm o
Figu e S8a, Suppo ing In o ma ion. The NF3 ibe is he e-
o e mainly composed o he δˊ-phase c ys alline s uc u e.
The (001) d-spacing amoun s o 1.40 nm, sligh ly la ge han
he MQS ilm, which is due o he highe ex ension o polyme
chains du ing elec ospinning. Howe e , u he inc ease in he
ibe diame e o 1000nm, NF4, he (100) and (010/110) e lec-
ions spli apa wi h a d-spacing o 0.413 and 0.410nm, which
indica es c ys alliza ion o he NF4 ibe in he ϒ-phase. This
is u he con i med by he (001) e lec ion wi h d-spacing o
1.49nm, which ma ches exac ly he one ob ained o he e e -
ence ϒ-phase ilm.[12]
Sol en e apo a ion a e plays a c ucial ole in o ma ion
o he piezoelec ic phase in nylon-11. To achie e he δʹ-phase
in hin- ilms, as sol en e apo a ion is needed. Fo NF1,
NF2, and NF3, due o he la ge su ace o olume a io o he
Figu e 1. a–d) Rep esen a i e SEM image o nano ibe s NF1 o NF4, showing bead- ee elec ospun nano ibe s. e) Dis ibu ion o ibe diame e o
NF1, NF2, NF3, and NF4 ibe s ob ained by measu ing o mo e han 100 ibe s om di e en SEM images.
Table 1. d-spacing calcula ed om XRD pa e ns o di e en samples.
Di ac ion
peaks
d-spacing [nm]
δʹ-phase ilm γ-phase ilm NF1 NF2 NF3 NF4
(001) 1.31 1.49 1.29 1.26 1.40 1.49
(100) 0.424 0.423 0.416 0.415 0.420 0.413
(010/110) 0.418 0.380 0.375 0.410
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nano ibe , he sol en e apo a ion a e is high. Howe e , due
o con inemen o he NF1 and NF2 ibe s o e y small dia-
me e s, he mechanical s e ching o he je du ing he elec-
ospinning induces highly o de ed α′-phase. Fo he NF4
ibe s, he dia me e is la ge and he sol en e apo a ion a e is
no as enough and he e o e ϒ-phase is o med. Fo he NF3
ibe , hese condi ions seem o be igh and he sol en e apo a-
ion a e is as enough o allow o ma ion o majo ly δʹ-phase.
The e o e, we specula e ha he nylon-11 ibe s, ob ained by
elec ospinning om TFA:ace one solu ion wi h diame e ange
be ween 100 o 1000nm, a e majo ly composed o δʹ-phase.
Th ough con olling he p ocessing condi ion, piezoelec ic
phase o nylon-11 can be eadily achie ed h ough elec ospin-
ning om TFA:ace one solu ion. The piezoelec ic ibe can be
he e o e employed o ha es ene gy om mechanical ib a-
ions. All he nano ibe s gene a e ol age pulses upon impac ,
i espec i e o he diame e . Figu e3a shows he gene a ed
ol age measu ed on he ibe ma unde open ci cui condi-
ion a he op imum ex e nal load, in esponse o a pe iodic
mechanical impac wi h a equency o 8 Hz. The ampli ude
o he ol age esponse s ongly changes wi h he ibe diam-
e e . The open ci cui ol age o he hin NF1 and NF2 ibe s
is below 0.6V, whe eas o he NF3 ibe he ol age inc eases
o 6V, bu hen dec eases again o 4V o he hick NF4 ibe .
The a eal powe ou pu o he ma s a e expe imen ally de e -
mined by impedance ma ching wi h an ex e nal load, as shown
in Figu e3b. All ma s ha a e es ed ha e simila hicknesses
o nea ly 50µm, he e o e olume ic powe gene a ed by he
nano ibe s ollows he same end albei di ided by hickness,
which is a same di ision ac o o all he nano ibe s. We no e
ha o he e en ual applica ion o he nano ibe s he a eal
powe densi y is a mo e ele an pa ame e .
The a eal powe ou pu o he ma s composed o NF1 and
NF2 ibe is low wi h a maximum powe o 0.03 µW cm−2
a 400 kΩ, whe eas he NF3 and NF4 deli e an a eal powe
ou pu o 3.1 µW cm−2 (a 500 kΩ) and 2.6 µW cm−2 (a 800 kΩ),
espec i ely. The ade-o be ween he ibe diame e and he
gene a ed ol age upon mechanical impac is di ec ly ela ed
o he c ys alline phases ha a e p esen in he ibe s. Besides
he c ys allini y, he ibe diame e also a ec s he gene a ed
Figu e 2. XRD di ac ion o elc ospun nylon-11 ibe s. The symbols show
he measu emen and he solid line show he decon olu ed peaks as well
as he calcula ed XRD di ac og ams.
Figu e 3. a) Open ci cui ou pu ol age o nylon-11 ibe s wi h a ious diame e s unde mechanical impac . b) Powe ou pu as a unc ion o load
esis ance o all nano ibe s wi h a ious diame e s.
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ol age. We will discuss he e ec o diame e in he las sec ion
o he manusc ip .
The NF3 ibe s a e e y sensi i e o mechanical exci a ions
due o hei c ys alliza ion in he elec oac i e δʹ-phase, which
makes hem a po en ial candida e o de ec ing mechanical
mo emen o body pa s. To demons a e he iabili y o he
NF3 nano ibe s o sensing applica ions, a nonwo en ma o
NF3 ibe s is placed on he hand, as shown in Figu e4b (inse ).
The nano ibe s de ec opening o closing o he is h ough
gene a ing ol age pulses as shown in Figu e4a. As shown in
Figu e 4b, he ou pu ol age inc eases and hen d ops upon
closing and opening he is , espec i ely. I should be no ed
ha he p o ile o he ol ages gene a ed is di ec ly ela ed o
he amoun o o ce exe ed on he nano ibe s upon bending,
which shows he sensi i i y o he ibe s o he ex e nal load.
NF3 nano ibe s a e he e o e capable o con e mechanical
ene gy om human mo ions in o elec ici y and enables he
de elopmen o wea able nanogene a o s based on nylon-11
ibe s. I should be no ed ha al hough ha es ing low e-
quency ene gy, pa icula ly in he Hz egime is echnically
challenging, employing he ecen ly de eloped plug-and-play
ene gy ha es ing ci cui s can u he boos he ou pu powe
o he nylon-11 ibe ene gy ha es e .[32]
Du abili y o he nano ibe upon con inuous mechanical
impac is an impo an ac o , which should be e alua ed i
nylon-11 ibe a e conside ed o ene gy ha es ing and sensing
applica ions. Figu e 4b shows he ol age gene a ed by NF3
a e expe iencing mechanical impac s o 0.2MPa, a an impac
equency o 8Hz o 35 h. The ibe s do no show any deg a-
da ion in ol age ou pu a e 106 impac s, indica ing du abili y
o he NF3 ibe s. No e ha he la ges elec ical powe a ail-
able om human ac i i y is om walking,[33] and 0.2 MPa is
equi alen o he mean p essu e be ween o e oo and heel o
an a e age human while walking.[34] Now, assuming ha he
equency o s eps is a ound 1Hz (one impac pe second), and
ha a pe son walks on a e age 2 h pe day, we would a i e a
s able ope a ion o a leas 140 days.
A las , we ha e pe o med ini e elemen me hod (FEM)
calcula ions o I) elucida e he ole o he diame e o nylon-11
ibe s on he ol age esponse, II) in es iga e he sensi i i y o
he ibe s owa d mechanical de o ma ions, and III) subs an-
ia e a p oposal ha subs an ially enhances he ol age gene a-
ion capabili y o he nylon-11 (o al e na i ely imp o e hei
sensi i i y o mechanical impac s). De ails o he calcula ion,
he mesh and he pa ame e s a e gi en in he supplemen a y
in o ma ion. The densi ies o αʹ and δʹ-phases a e aken as
1.17 and 1.04, espec i ely.[35] The con en s o simula ion o
δʹ and αʹ-phases a e aken om li e a u e.[16] A simpli ied
nano ibe wi h a iable diame e and ixed leng h o 500 nm
is used, because he ocus o he FEM simula ion is o gain
insigh a he han ep oducing he complex expe imen al
si ua ion (de ails o he simula ion a e gi en in Figu e S10,
Suppo ing In o ma ion). I is assumed ha he nano ibe s
a e sel -poled and he pola iza ion axis is along he diame e
in he z-di ec ion, and in pa allel wi h he applied mechanical
s ess. In p ac ice, he elec ical ou pu s o nylon-11 nano ibe
ma s a e gene a ed om a complex ne wo k o such sec ions
connec ed in se ies and pa allel. Fi s , we ha e conside ed wo
cases o hin and hick diame e s o 55 and 200 nm, espec-
i ely, which co esponds o he cases o NF1 αʹ-phase and NF3
δʹ-phase ibe s. A i s , bo h ibe s expe ience he same cyclic
mechanical impac o 0.25MPa. The calcula ed peak ol ages
o bo h cases a e p esen ed in Figu e5a. The calcula ed peak
ol age o he hin αʹ-phase ibe is only 3 mV, whe eas he
peak ol age ou pu o he hicke δʹ-phase ibe is ou imes
la ge and amoun s o 12mV. The calcula ion shows a ac o o
4 inc ease in peak ol age o he nano ibe s wi h an inc ease
in ibe diame e om 55 o 200nm. Expe imen ally, he peak
ol age o NF3 is 6V, which is abou en imes la ge han NF1
(≈0.6V). The e o e, he e is easonable ag eemen be ween he
simula ion and expe imen , conside ing he simpli ied model.
Hence, he di e ence in he gene a ed ol ages by he di e en
nano ibe s can be p ima ily asc ibed o he c ys alline phase o
nylon-11 in which he ibe is c ys allized.
The δʹ-phase nylon-11 ibe is e y sensi i e o he applied
p essu e, as shown in Figu e 5b, whe e he gene a ed peak
ol age is calcula ed o he ibe s unde a iable p essu e.
While bo h ibe s show inc ease in he peak ol age, he δʹ-
phase ibe shows a much s eepe inc ease in peak ol age.
F om he slope o he cu es we ob ained heo e ical sensi i i y
o 0.13 mV kPa−1 o he δʹ-phase ibe whe eas he αˊ-phase
ibe s has only 0.02mV kPa−1.
The FEM simula ion wi h a ela i ely good accu acy cap-
u es he physics behind he supe io pe o mance o δˊ-
phase NF3 ibe in ene gy ha es ing and sensing. Hence,
he model can be employed o e alua e di e en p oposals o
enhance he peak ol age o he δʹ-phase nylon-11 ibe . I has
been shown ha ene gy ha es e s based on po ous P(VDF-
T FE) ilms as well as nano ibe s, wi h po es ha a e con-
ined inside he polyme , show enhanced powe ou pu o he
Figu e 4. a) Real- ime body mo ion moni o ing: a piezoelec ic nanogene a o is a ached o palm which gene a es elec ical signals upon closing and
opening he is . b) Zoom-in o (a). The inse shows he pho og aphs o he ibe senso a ached o he hand and he ou pu signals gene a ed upon
opening and closing o he is . The signals a e de ec ed by an oscilloscope. c) Open ci cui ol age o he NF3 nano ibe s be o e and a e con inuous
impac ing o 105 s a a equency o 8Hz.
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gene a o .[36] In he nex s ep o FEM simula ions we he e o e
in oduced sphe ical ai ca i ies inside he δʹ-phase nano ibe .
The peak ol age is calcula ed o a ixed p essu e o 250kPa
o s ess-cha ge mode. Figu e 5c shows a g aphical p o ile
o he gene a ed ol age in he ibe wi h 37.5% po osi y. The
calcula ed peak ol age as a unc ion o po osi y is plo ed in
Figu e5d. The solid-co e δʹ-phase nano ibe p oduces a peak
ol age o 32 mV. The peak ol age mono onically inc eases
as he po osi y enhances and eaches alues as high as 61mV.
The enhancemen o he peak ol age is due o lowe ing o
he ela i e pe mi i i y and he enhancing de o mabili y
o he nano ibe s upon inc easing he amoun s o po es. Fo a
po ous dielec ic ilm consis ing o sphe ical closed po es, he
ela i e pe mi i i y, ε′, dec eases mono onically wi h he ac-
ional po osi y, P, as[36,37] P
PP
εε
()
′=−
ε
εε
−
+− +
13( 1)
12
, whe e, ε = 4[22]
is he ela i e dielec ic pe mi i i y o nylon-11. Fo he ideal
case o uni o mly dis ibu ed isola ed sphe ical po es, he die-
lec ic pe mi i i y con inuously d ops as po osi y inc eases o
2.67 o a ibe ha is 37.5% po ous. Mo eo e , po osi y sub-
s an ially modi ies he s i ness, speci ically he elas ic com-
p essibili y cons an σ33 o he δʹ-phase nylon-11 nano ibe s.
Bo h o hese con ibu ions a e esponsible o he enhanced
peak ol age in he p oposed po ous nano ibe s. Expe imen-
ally, a ious me hods ha e been success ully exploi ed o he
ab ica ion o po ous nano ibe s o non-piezoelec ic nylons,
which ende s po ous nylon-11 ibe a e y p omising candi-
da e o he ealiza ion o highly e icien ene gy ha es e s o
sensi i e p essu e senso s.[38–40]
3. Conclusions
Piezoelec ic nylon-11 nano ibe s a e p oduced by elec ospin-
ning om nylon-11 solu ion in TFA:ace one. The diame e o
he nano ibe s plays a c ucial ole in o de o achie e he sel -
poled highly piezoelec ic δˊ-c ys alline phase. I is pos ula ed
ha o ma ion o he δˊ-phase is due o he in e play be ween
he sol en mix u e used o elec ospinning, TFA:ace one, he
sol en e apo a ion a e and he pulling o ce ac ing on he
ibe du ing he elec ospinning p ocess. The elec ical ac i i y
o he esul ing nano ibe s is maximum o he ibe s ha a e
c ys alized in δʹ-phase ha p oduce a ol age as high as 6 V
unde mechanical impac , ende ing he nylon-11 ibe s a e y
p omising candida e o wea able elec ici y gene a o s. Mo e-
o e , he g ea sensi i i y o he δʹ-phase nylon-11 ibe s o p es-
su e can be exploi ed in sensing applica ions. I is subs an ia ed
h ough ini e elemen modeling ha in oducing po osi y
inside he ibe s is a iable ou e o enhance he ol age ou pu .
The demons a ion o piezoelec ic nylon ibe s and concomi-
an guidelines o ou pu powe op imiza ion opens a new
ou e owa d ealiza ion o sma and elec onic ex iles based
on nylons.
4. Expe imen al Sec ion
Ma e ials: Nylon-11 was pu chased om Sigma Ald ich. TFA and
ace one (99.8%, Ex a D y), we e pu chased om Ca l Ro h Gmbh and
ACROS O ganics, espec i ely.
Figu e 5. a) The g aphic o he FEM simula ion o he δʹ-phase NF3 and αʹ-phase NF1 ibe s unde cyclic p essu e o 250kPa. b) The calcula ed ol age
o m he same ibe s as a unc ion o he applied p essu e. c) The g aphical simula ion o he ol age peak o he δ′-phase NF3 ibe a a po osi y o
37.5% unde applied p essu e o 250kPa. d) The calcula ed peak ol age as unc ion o po osi y unde applied p essu e o 250kPa.
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Solu ion P epa a ion and Elec ospinning: Fi s , he pelle s o nylon-11
we e d ied in acuum o en a 40 °C o 48 h. Nylon-11 solu ions (di e en
concen a ion: 5, 10, 15, and 20 w %) we e p epa ed by dissol ing
polyme in TFA and ace one mix u e (60:40 mol%). The elec ospinning
p ocess was ca ied ou using a se up ab ica ed by IME Technologies
wi h an applied ol age o 15–25 kV, a wo king dis ance be ween he
spinne e and he collec o o 15–25cm, and a eeding a e anging om
0.0025 o 1.0mL h−1 as shown in Table2. Nano ibe s we e collec ed on
aluminum oils. The schema ic o he elec ospinning se up is gi en in
Figu e S3, Suppo ing In o ma ion.
As compa ison, MQS ilms we e p epa ed by ho p essing
nylon-11 pelle s a 210 °C o 2 min and immedia ely quenching in
d yice–isop opanol solu ion. The ilms we e uniaxially s e ched a oom
empe a u e wi h a d aw a io o 3:1 a s ain a e o 5mm min−1 using
a uni e sal es ing machine (Zwick Roell-Z005). The ϒ-phase o he
nylon-11 ilm was ob ained by slow e apo a ion o he sol en a oom
empe a u e a e d op cas ing he nylon-11 solu ion in TFA in a pe i dish.
Mic os uc u e In es iga ion: The diame e and mo phology o
nano ibe s we e examined wi h a Gemini 1530 (Ca l Zeiss AG,
Obe kochen, Ge many) SEM, ope a ing a an accele a ing ol age o
0.35 kV. The nano ibe samples o SEM we e p epa ed by deposi ing
elec ospun nano ibe s di ec ly on silicon wa e s o abou 5 s du ing
elec ospinning. The c ys alline s uc u es o he ibe s and MQS ilm
we e in es iga ed using an XRD (Philips Powde Di ac ome e PW1820)
using Cu adia ion (l= 1.5418 Å).
Mechanical Impac Se up: The open ci cui ol age was measu ed by
an oscilloscope (LeC oy wa e unne LT372) wi h an inpu esis ance o
1 MΩ. The nanogene a o s we e subjec ed o pe iodic mechanical impac s
a 8Hz a an impac p essu e o 0.2MPa using a home-buil se -up.
Fibe Senso : A ma o ibe s was placed on o a human hand o eal-
ime mo ion de ec ion. The mo ions o hand, by closing and opening o he
is , we e eco ded by oscilloscope. As nylons we e ine and non-haza dous
ma e ials, hey we e widely used in wea able ex iles, hence had he
po en ial o be used as non-in asi e heal h moni o ing senso s. In o med,
w i en consen om he pa icipan in he es was ob ained p io o he
expe imen .
Suppo ing In o ma ion
Suppo ing In o ma ion is a ailable om he Wiley Online Lib a y o
om he au ho .
Acknowledgemen s
S.A. M.H.A, M.M.A, and K.A. acknowledge he inancial suppo o
he Alexande on Humbold Founda ion (Ge many) h ough he
So ja Ko ale skaja Awa d, and he echnical suppo om he Max-
Planck Ins i u e o Polyme Resea ch. S.A. hanks he Na ional
Uni e si y o  Science and Technology (Pakis an) o he inancial
suppo . The au ho s wish o hank P o . Paul. W. M. Blom o ui ul
discussions and D . Man ed Wagne o he NMR measu emen .
Open access unding enabled and o ganized by P ojek DEAL.
Con lic o In e es
The au ho s decla e no con lic o in e es .
Keywo ds
ene gy ha es ing, nylon ibe s, piezoelec ic de ices, senso s, sma
ex iles
Recei ed: May 19, 2020
Re ised: Augus 16, 2020
Published online:
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Table 2. P ocessing pa ame e s o elec ospinning and he esul an
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Sample Solu ion
concen a ion
[w %]
Applied
ol age
[kV]
Dis ance
be ween
spinne e and
collec o [cm]
Feed
a e
[mL h−1]
Mean ibe
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NF1 5 15 15 0.05 55 ± 10
NF2 10 15 15 0.05 100 ± 20
NF3 15 15 15 0.1 200 ± 30
NF4 20 15 15 0.1 1000 ± 300
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