Ci a ion: Ma ín-Aye di, A.;
Rubio-Peña, L.; Peˇ inka, N.;
Oya zabal, I.; Vilas, J.L.; Cos a, P.;
Lance os-Méndez, S. Towa ds
Sus ainable Tempe a u e Senso
P oduc ion h ough CO2-De i ed
Polyca bona e-Based Composi es.
Polyme s 2024,16, 1948. h ps://
doi.o g/10.3390/polym16131948
Academic Edi o : Iolanda De Ma co
Recei ed: 5 June 2024
Re ised: 27 June 2024
Accep ed: 2 July 2024
Published: 8 July 2024
Copy igh : © 2024 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/).
polyme s
A icle
Towa ds Sus ainable Tempe a u e Senso P oduc ion h ough
CO2-De i ed Polyca bona e-Based Composi es
Ane Ma ín-Aye di 1, Luis Rubio-Peña 2, Nikola Peˇ inka 1,* , I zia Oya zabal 1,3, JoséL. Vilas 1,4 ,
Ped o Cos a 5,6 and Senen xu Lance os-Méndez 1,3,5,*
1BCMa e ials, Basque Cen e o Ma e ials, Applica ions and Nanos uc u es, UPV/EHU Science Pa k,
48940 Leioa, Spain; [email p o ec ed] (A.M.-A.); i zia [email p o ec ed] (I.O.);
[email p o ec ed] (J.L.V.)
2Enginee ing School, Uni e si y o Cadiz, A da. de la Uni e sidad de Cádiz, 10, 11519 Pue o Real, Spain;
[email p o ec ed]
3IKERBASQUE, Basque Founda ion o Science, 48013 Bilbao, Spain
4
Mac omolecula Chemis y G oup (LABQUIMAC), Depa men o Physical Chemis y, Facul y o Science and
Technology, Uni e si y o he Basque Coun y (UPV/EHU), Ba io Sa iena s/n, 48940 Leioa, Spain
5Physics Cen e o Minho and Po o Uni e si ies (CF-UM-UP) and Labo a o y o Physics o Ma e ials and
Eme gen Technologies (LapMET), Uni e si y o Minho, Campus o Gual a , 4710-057 B aga, Po ugal;
[email p o ec ed]
6
IB-S Ins i u e o Science and Inno a ion o Sus ainabili y, Uni e sidade do Minho, 4710-057 B aga, Po ugal
*Co espondence: [email p o ec ed] (N.P.); [email p o ec ed] (S.L.-M.)
Abs ac : The s eep inc ease in ca bon dioxide (CO
2
) emissions has c ea ed g ea conce n due o i s
ole in he g eenhouse e ec and global wa ming. One app oach o mi iga e CO
2
le els in ol es i s
applica ion in speci ic echnologies. In his con ex , CO
2
can be used o a mo e sus ainable syn hesis
o polyca bona es (CO
2
-PCs). In his esea ch, CO
2
-PC ilms and composi es wi h mul iwalled
ca bon nano ubes (MWCNTs, anging om 0.2 o 7.0 w .%) ha e been p epa ed o achie e mo e
sus ainable mul i unc ional sensing de ices. The inclusion o he ca bonaceous ille s allows o he
elec ical conduc i i y o be enhanced, eaching he pe cola ion h eshold (P
c
) a 0.1 w .% MWCNTs
and a maximum elec ical conduc i i y o 0.107 S
·
m
−1
o he composi e con aining 1.5 w .% MWC-
NTs. The composi e con aining 3.0 w .% MWCNTs was also s udied, showing a s able and linea
esponse unde empe a u e a ia ions om 40 o 100
◦
C and om 30 o 45
◦
C, wi h a sensi i i y o
1.3 ×10−4◦C−1
. Thus, his in es iga ion demons a es he possibili y o employing CO
2
-de i ed
PC/MWCNT composi es as he mo esis i e sensing ma e ials, allowing o he ansi ion owa ds
sus ainable polyme -based elec onics.
Keywo ds: polyca bona e; lexible elec onics; ca bon nano ubes; senso ; he mo esis i e
1. In oduc ion
In ecen yea s, he e has been inc easing conce n abou he s eep inc emen in ca bon
dioxide (CO
2
) le els, which is associa ed wi h global wa ming and he g eenhouse e ec [
1
].
Acco ding o EDGAR, he Emissions Da abase o Global A mosphe ic Resea ch, CO
2
emissions inc eased om 1990 o 2021 in he ollowing manne : 87% due o he powe
indus y, 65% due o o he indus ial combus ion, 66% due o anspo , 2% due o building-
ela ed emissions, and 101% due o emissions om o he sec o s. I is wo h highligh ing
ha in 2020, a educ ion in CO
2
emissions was eco ded due o he COVID-19 pandemic.
Ne e heless, in 2021, global emissions ebounded o each 37.9 G , compa able o he
le els obse ed in 2019 be o e he pandemic [2].
CO
2
ep esen s an abundan eeds ock; he e o e, se e al e o s ha e been made o
ha ness he po en ial o his gas h ough ecycling and eu iliza ion, wi h he aim o bol-
s e ing he ci cula economy while concu en ly mi iga ing i s en i onmen al oo p in [
3
].
Polyme s 2024,16, 1948. h ps://doi.o g/10.3390/polym16131948 h ps://www.mdpi.com/jou nal/polyme s
Polyme s 2024,16, 1948 2 o 13
Some examples o accomplish he in ended goal in ol e he use o CO
2
in chemical p oduc-
ion, including o mic acid [
4
], u ea [
5
], o in he syn hesis o CO
2
-based polyca bona es
(CO2-PCs) [6].
PCs a e polyme s composed o ca bona e (-O-(C=O)-O-) monome ic uni s which a e e-
pea ed along he polyme chain. The physical–chemical p ope ies o his
polyme —op ical
anspa ency, high he mal s abili y, and high ensile
s eng h [7,8]—allow
i s applica ion in
se e al ields, including biomedicine [
9
], au omo i e [
10
], and elec onics [
11
]. Pe oleum-
de i ed PCs a e gene ally syn hesized om bisphenol A (BPA), which usually imp o es
PC esis ance and du abili y [
12
], and phosgene. I has o be highligh ed ha hese eagen s
a e qui e oxic. Phosgene is a poisonous gas, whe eas BPA is a ho mone and endoc ine-
dis up ing chemical, as well as a neu o oxic and ca cinogenic agen [
13
,
14
]. Consequen ly,
g een chemis y and en i onmen ally iendly app oaches o ob ain PC monome ic uni s
ha e been explo ed. An al e na i e elies on he copolyme iza ion o CO
2
and epoxide,
which elimina es he need o oxic and en i onmen ally ha m ul eagen s such as phosgene
and bisphenol A, as illus a ed in Scheme 1[15].
Polyme s 2024, 16, x FOR PEER REVIEW 2 o 13
[3]. Some examples o accomplish he in ended goal in ol e he use o CO2 in chemical
p oduc ion, including o mic acid [4], u ea [5], o in he syn hesis o CO2-based polyca -
bona es (CO2-PCs) [6].
PCs a e polyme s composed o ca bona e (-O-(C=O)-O-) monome ic uni s which a e
epea ed along he polyme chain. The physical–chemical p ope ies o his polyme —
op ical anspa ency, high he mal s abili y, and high ensile s eng h [7,8]—allow i s ap-
plica ion in se e al ields, including biomedicine [9], au omo i e [10], and elec onics [11].
Pe oleum-de i ed PCs a e gene ally syn hesized om bisphenol A (BPA), which usually
imp o es PC esis ance and du abili y [12], and phosgene. I has o be highligh ed ha
hese eagen s a e qui e oxic. Phosgene is a poisonous gas, whe eas BPA is a ho mone
and endoc ine-dis up ing chemical, as well as a neu o oxic and ca cinogenic agen [13,14].
Consequen ly, g een chemis y and en i onmen ally iendly app oaches o ob ain PC
monome ic uni s ha e been explo ed. An al e na i e elies on he copolyme iza ion o CO2
and epoxide, which elimina es he need o oxic and en i onmen ally ha m ul eagen s
such as phosgene and bisphenol A, as illus a ed in Scheme 1 [15].
Scheme 1. Polyca bona e syn hesis om pe oleum (abo e) and CO2 (below).
PCs ha e ound ex ensi e use in he elec onics sec o , p ima ily as an insula ing
laye . Fo ins ance, he moplas ic polyca bona e/ac yloni ile–bu adiene–s y ene blends
(PC/ABS) ha e been inco po a ed in o elec onic de ices, which impa no only insula -
ing p ope ies bu also lame- e a dan cha ac e is ics o he de ices [16]. Addi ionally,
PCs ha e been used as ma ices o de elop conduc i e composi es. E en hough hey a e
dielec ic polyme s, elec ical conduc i i y p ope ies can be p o ided by adding conduc-
i e ca bonaceous nano ille s o he ma ix, including ca bon nano ubes (CNTs) [17], g a-
phene (G) [18], and ca bon black (CB) [19]. In ac , one o he main app oaches o ob ain
conduc i e PC composi es in ol es he inco po a ion o CNTs, as hey exhibi a high as-
pec a io, la ge elec ical conduc i i y alues o 105 S·cm−1, an elas ic modulus o 1 TPa,
and he mal conduc i i y alues anging om 3000 o 6000 W·mK [20,21]. Fu he mo e,
he high aspec a io o CNTs enables polyme /CNT hyb id ma e ials o exhibi elec ical
conduc i i y abo e he pe cola ion h eshold (Pc) a low CNT concen a ions. The concen-
a ion depends on ac o s such as he nano ube mo phology (single o mul iwalled), p o-
cessing me hod (ex usion o sol en cas ing), and dispe sion quali y [22]. The e o e, he
dielec ic polyme ic ma ix can be ans o med in o a conduc i e composi e [23,24].
The e is a wide op ion o polyme s o composi e p ocessing. Ne e heless, a g een
ansi ion o en i onmen ally iendly elec ically conduc i e composi es is highly neces-
sa y. In e es ingly, he ield o biopolyme /nano ille composi es has led o nume ous
b eak h oughs in ecen yea s. Biopolyme s a e selec ed o hei na u al o igin, abun-
dance, enewabili y, and, in some cases, hei abili y o dissol e in wa e , which a oids
he use o o ganic sol en s [25]. All in all, hese effo s suppo he equi ed educ ion in
he en i onmen al impac o he ma e ials used in senso and ac ua o applica ions [26,27].
Fo example, i s na u al o igin and physical–chemical p ope ies make silk ib oin a
biopolyme o s udy. In his case, i has been ein o ced by sol en cas ing wi h CNTs o
Scheme 1. Polyca bona e syn hesis om pe oleum (abo e) and CO2(below).
PCs ha e ound ex ensi e use in he elec onics sec o , p ima ily as an insula ing
laye . Fo ins ance, he moplas ic polyca bona e/ac yloni ile–bu adiene–s y ene blends
(PC/ABS) ha e been inco po a ed in o elec onic de ices, which impa no only insula ing
p ope ies bu also lame- e a dan cha ac e is ics o he de ices [
16
]. Addi ionally, PCs
ha e been used as ma ices o de elop conduc i e composi es. E en hough hey a e di-
elec ic polyme s, elec ical conduc i i y p ope ies can be p o ided by adding conduc i e
ca bonaceous nano ille s o he ma ix, including ca bon nano ubes (CNTs) [
17
], g aphene
(G) [
18
], and ca bon black (CB) [
19
]. In ac , one o he main app oaches o ob ain conduc-
i e PC composi es in ol es he inco po a ion o CNTs, as hey exhibi a high aspec a io,
la ge elec ical conduc i i y alues o 10
5
S
·
cm
−1
, an elas ic modulus o 1 TPa, and he mal
conduc i i y alues anging om 3000 o 6000 W
·
mK [
20
,
21
]. Fu he mo e, he high aspec
a io o CNTs enables polyme /CNT hyb id ma e ials o exhibi elec ical conduc i i y
abo e he pe cola ion h eshold (P
c
) a low CNT concen a ions. The concen a ion de-
pends on ac o s such as he nano ube mo phology (single o mul iwalled), p ocessing
me hod (ex usion o sol en cas ing), and dispe sion quali y [
22
]. The e o e, he dielec ic
polyme ic ma ix can be ans o med in o a conduc i e composi e [23,24].
The e is a wide op ion o polyme s o composi e p ocessing. Ne e heless, a g een
ansi ion o en i onmen ally iendly elec ically conduc i e composi es is highly nec-
essa y. In e es ingly, he ield o biopolyme /nano ille composi es has led o nume ous
b eak h oughs in ecen yea s. Biopolyme s a e selec ed o hei na u al o igin, abundance,
enewabili y, and, in some cases, hei abili y o dissol e in wa e , which a oids he use
o o ganic sol en s [
25
]. All in all, hese e o s suppo he equi ed educ ion in he
en i onmen al impac o he ma e ials used in senso and ac ua o applica ions [26,27].
Fo example, i s na u al o igin and physical–chemical p ope ies make silk ib oin a
biopolyme o s udy. In his case, i has been ein o ced by sol en cas ing wi h CNTs o
Polyme s 2024,16, 1948 3 o 13
piezo esis i e senso ab ica ion [
28
]. O he example includes g aphene ille s dispe sed
in o sodium ca boxyme hyl cellulose ma ix by sol en cas ing o de o ma ion sensing.
The senso has been p ocessed ollowing wa e -based o mula ion. This makes i a ac i e
as he use o o ganic sol en s is a oided. E en mo e, i shows he mo esis i e sensi i i y o
S =
−
0.27 and piezo esis i e Gauge Fac o s (GF) o 1 < GF < 5 [
27
]. None heless, bio-based
polyme composi es s ill aise conce ns wi h espec o senso esponse s abili y o e ime.
Ne e heless, biopolyme s a e no he only way o achie e senso s ollowing g een
chemis y. The upcycling o ma e ials, he euse o was e in o he applica ions, is a sui able
al e na i e o ob ain high-pe o mance ma e ials while suppo ing sus ainable app oaches.
In his scope, we sugges he de elopmen o PC-based sensing composi es. This ma e-
ial has gained popula i y due o he inc easing demand o senso ma e ials d i en by
he digi aliza ion o socie y and he In e ne o Things concep . Consequen ly, nume ous
s udies ha e explo ed he syn hesis o PC/MWCNT composi es as piezoelec ic senso s.
Fo ins ance, P. Cos a e al. achie ed composi es wi h a P
c
alue o 0.3 w .% and Gauge
Fac o s be ween 1.1 < GF < 1.75 and 0.1 < GF < 0.4, espec i ely, o uniaxial s ain and
ou -poin -bending expe imen s, which could be applied in ae onau ics [
29
]. Addi ionally,
he e ha e been signi ican ad ancemen s made in p ocessing PC blends o enhance ma ix
cha ac e is ics and make hem sui able o he a o emen ioned applica ions. Fo ins ance,
P(VDF-HFP)/PC/MWCNT composi es wi h piezo esis i e sensing capabili ies we e p e-
pa ed by mel spinning [
30
]. In he case o PC-CO
2
, he e a e di e en epo s conce ning
hei syn hesis [
31
,
32
], as well as hei physical–chemical cha ac e iza ion depending on
chain leng h [
33
–
35
]. Ne e heless, he e is a sca ci y o li e a u e conce ning CO
2
-PCs
combined wi h CNTs o sensing pu poses. Consequen ly, he p esen s udy p oposes
CO
2
-de i ed PC/MWCNT composi es o empe a u e senso applica ions. The mo esis-
i e senso s ely on he a ia ion in elec ical esis ance o he ma e ial wi h empe a u e,
and he p ecise he mo esis i e cha ac e is ics depend on ac o s such as he ype and
dispe sion o he ille , ille dimensions, and speci ic chemical cha ac e is ics o bo h he
polyme and he ille [36].
In summa y, his in es iga ion p oposes an en i onmen ally iendly app oach o
he ab ica ion o elec onic ma e ials and de ices, as exempli ied by he de elopmen o
a he mo esis i e sensing ma e ial. The app oach in ol es he use o a poly (cyclohex-
ene ca bona e) (PCC) ma ix syn hesized om CO
2
o de elop composi es wi h MWC-
NTs h ough a sol en cas ing p ocess. The in es iga ion includes he e alua ion o he
mo phological, he mal, and elec ical p ope ies o he ilms, as well as hei unc ional
he mosensi i e capabili ies.
2. Ma e ials and Me hods
2.1. Reagen s
Comme cial QPAC
®
130 poly (cyclohexene ca bona e) PCC was pu chased as pel-
le s om Empowe Ma e ials Inc., New Cas le, DE, USA. The ma e ial shows a densi y
o 1.10 g
·
cm
−3
, onse es ima e decomposi ion empe a u e o 250
◦
C, and a glass ansi-
ion empe a u e (T
g
) o 120–130
◦
C. As conduc i e ille s, mul iwalled ca bon nano ubes
(MWCNTs) wi h e e ence NC7000™ we e p o ided by Nanocyl, S.A, Samb e ille, Bel-
gium. MWCNTs we e manu ac u ed by chemical apo deposi ion, showing a ca bon
pu i y o
≈
90%, an a e age diame e o
≈
9.5 nm, and an a e age leng h o
≈
1.5
µ
m.
Dichlo ome hane (DCM) was supplied om Sigma Ald ich (Bu ling on, MA, USA) and
was used o dissol e he polyme and o dispe se he MWCNTs.
2.2. Composi e Films P ocessing
P is ine PCC ilms and PCC/MWCNT composi es we e p epa ed by he sol en
cas ing me hod, as indica ed in Scheme 2. P is ine PCC ilms we e p epa ed by sol ing 2 g
o polyme in 12 mL o DCM and s i ing o 2 h a oom empe a u e (RT). Composi es
we e p epa ed in wo s eps. In he i s s ep, 2 g o polyme was dissol ed in 6 mL o DCM
by s i ing igo ously o 2 h a RT. Meanwhile, di e en amoun s o MWCNTs (0.2, 0.5,
Polyme s 2024,16, 1948 4 o 13
1.0, 1.5, 3.0, 5.0, and 7.0 w .% wi h espec o he polyme ) we e weigh ed and 6 mL o
sol en was added o hem. The esul ing suspensions we e ea ed in an ul asound ba h
o 3 h a 25
◦
C o imp o e deagglome a ion and dispe sion. In he second s ep, nano ille s
we e mixed wi h he polyme solu ion, and he esul ing mix u e was s i ed o 2 h. In
bo h cases, ei he wi h he p is ine polyme o composi e solu ions, he solu ions we e
pou ed on o a clean glass su ace and ilms we e subsequen ly p oduced using a D . Blade.
Finally, he esul ing ilms we e d ied o 24 h a RT o ensu e sol en e apo a ion. A e
his p ocess, ilms wi h an a e age hickness o 154 ±27 µm we e ob ained.
Polyme s 2024, 16, x FOR PEER REVIEW 4 o 13
p epa ed in wo s eps. In he i s s ep, 2 g o polyme was dissol ed in 6 mL o DCM by
s i ing igo ously o 2 h a RT. Meanwhile, diffe en amoun s o MWCNTs (0.2, 0.5, 1.0,
1.5, 3.0, 5.0, and 7.0 w .% wi h espec o he polyme ) we e weigh ed and 6 mL o sol en
was added o hem. The esul ing suspensions we e ea ed in an ul asound ba h o 3 h
a 25 °C o imp o e deagglome a ion and dispe sion. In he second s ep, nano ille s we e
mixed wi h he polyme solu ion, and he esul ing mix u e was s i ed o 2 h. In bo h
cases, ei he wi h he p is ine polyme o composi e solu ions, he solu ions we e pou ed
on o a clean glass su ace and ilms we e subsequen ly p oduced using a D . Blade. Fi-
nally, he esul ing ilms we e d ied o 24 h a RT o ensu e sol en e apo a ion. A e
his p ocess, ilms wi h an a e age hickness o 154 ± 27 µm we e ob ained.
Scheme 2. Sequen ial p ocessing o p is ine polyme and composi es.
2.3. Cha ac e iza ion
All samples we e cha ac e ized in e ms o mo phology, he mal, mechanical, and
elec ical p ope ies. The mo phology o he samples was s udied wi h a Hi achi S-4800
Scanning Elec on Mic oscope (SEM) o e alua e he dis ibu ion o MWCNTs wi hin he
PCC ma ix. Images we e ob ained a an accele a ing ol age o 5.0 KV and magni ica ions
o ×50.0K and ×100K.
A enua ed o al e lec ance–Fou ie - ans o m in a ed spec oscopy (ATR-FTIR)
was used o analyze possible in e ac ions be ween he polyme and he ille . In a ed
spec a we e collec ed wi h a Nicole Nexus FTIR spec opho ome e (The mo Elec on
Co po a ion, Wal ham, MA, USA) in he ange o 400 o 4000 cm−1 wi h a esolu ion o 4
cm−1 and a e aging 64 scans pe spec um.
The mal cha ac e iza ion was pe o med by The mog a ime ic Analysis (TGA) and
Diffe en ial Scanning Calo ime y (DSC). TGA was measu ed in a Me le Toledo
TGA/SDTA851e he mobalance (Japan) o e alua e he maximum deg ada ion
Scheme 2. Sequen ial p ocessing o p is ine polyme and composi es.
2.3. Cha ac e iza ion
All samples we e cha ac e ized in e ms o mo phology, he mal, mechanical, and
elec ical p ope ies. The mo phology o he samples was s udied wi h a Hi achi S-4800
Scanning Elec on Mic oscope (SEM) o e alua e he dis ibu ion o MWCNTs wi hin he
PCC ma ix. Images we e ob ained a an accele a ing ol age o 5.0 KV and magni ica ions
o ×50.0K and ×100K.
A enua ed o al e lec ance–Fou ie - ans o m in a ed spec oscopy (ATR-FTIR) was
used o analyze possible in e ac ions be ween he polyme and he ille . In a ed spec a
we e collec ed wi h a Nicole Nexus FTIR spec opho ome e (The mo Elec on Co po a ion,
Wal ham, MA, USA) in he ange o 400 o 4000 cm
−1
wi h a esolu ion o 4 cm
−1
and
a e aging 64 scans pe spec um.
The mal cha ac e iza ion was pe o med by The mog a ime ic Analysis (TGA)
and Di e en ial Scanning Calo ime y (DSC). TGA was measu ed in a Me le Toledo
TGA/SDTA851e he mobalance (Japan) o e alua e he maximum deg ada ion empe a-
u e (T
max
). Samples (~10–15 mg) we e weigh ed and hea ed om 25 o 800
◦
C a a hea ing
a e o 10
◦
C
·
min
−1
unde a ni ogen a mosphe e. Fo each sample, he maximum deg a-
da ion empe a u e (T
dmax
) was calcula ed om he i s de i a i e. The mal ansi ions
Polyme s 2024,16, 1948 5 o 13
we e measu ed wi h a Me le Toledo model DSC 822e calo ime e (G ei ensee, Swi ze -
land). Samples (~10 mg) we e sealed in o aluminum pans and subjec ed o a empe a u e
cycle anging om
−
70 o 250
◦
C, ollowed by cooling om 250 o
−
70
◦
C. The he mal
p og am consis ed o successi e hea ing, cooling, and hea ing scans, whe e he i s scan
was pe o med o emo e he he mal his o y o he samples, while T
g
was de e mined
om he second hea ing scan.
The s udy o he mechanical p ope ies allowed us o de e mine he ini ial modulus,
maximum s ess, and s ain. All samples we e measu ed in ensile mode using a Shimadzu
AG-IS uni e sal (Japan) es ing machine equipped wi h a load cell o 500 N. Rec angula
samples wi h app oxima e dimensions o 10 mm
×
50 mm
×
154
µ
m we e es ed a a
cons an eloci y o 1 mm
·
min
−1
. Each sample was measu ed i e imes. The ini ial
modulus was calcula ed up o 0.20% s ain.
The elec ical conduc i i y as a unc ion o ille con en and he co esponding pe -
cola ion h eshold (P
c
) we e de e mined a e measu ing he samples wi h a Kei hley 487
picoamme e / ol age sou ce. Measu emen s we e ca ied ou by applying a ol age ang-
ing om
−
10 V o +10 V wi h a s ep o 1 V in he di ec cu en mode a RT and measu ing
he cu en . P io o measu emen s, 5 mm diame e ci cula gold elec odes we e deposi ed
on bo h sides o he samples using a Quo um Q150T S spu e coa e (Quo um Technologies,
Ken , UK). The elec ical conduc i i y o he samples was de ined as he in e se o he
esis i i y (
ρ
), which was de e mined om he esis ance (R) ex ac ed om he I–V esul s
ollowing Equa ion (1), whe e Lis he hickness o he sample and Ais he a ea o he
elec odes.
σ=1
ρ=L
RA (1)
Finally, he mo esis i e es s we e conduc ed o assess he sui abili y o he composi es
as empe a u e senso s. The he mo esis i e pe o mance o he PCC/MWCNT composi es
wi h 3.0 w .% MWCNTs con en was measu ed using an Agilen 34401A mul ime e
synch onized wi h a Linkam THMSE600 empe a u e o en. Sil e ink ( om Aga Scien i ic,
S ans ed Moun i che , UK, e e ence AGG3790) was used as a pa allel conduc i e elec ode,
and elec ical con ac o he mul ime e was pe o med wi h coppe wi es. The hea ing–
cooling p o ile was di ided in o wo di e en cycles, om 30 o 45
◦
C and om 40 o
100 ◦C.
S=∆R/R0
∆T(2)
The he mo esis i e sensi i i y (S) was de e mined acco ding o Equa ion (2), whe e
∆
Rand R
0
a e he elec ical esis ance a ia ion and he ini ial esis ance (in
Ω
), espec i ely,
and ∆Tis he empe a u e a ia ion (in ◦C).
3. Resul s
3.1. Mo phological and Chemical Cha ac e is ics
The mo phology o he samples was e alua ed by SEM images o analyze nano ille
dispe sion wi hin he ma ix. Rep esen a i e su ace and c oss-sec ion images a e shown
in Figu e 1. The p is ine PCC ilm shows a la su ace and a compac mo phology, hough
he p esence o some oids is obse ed, which can be a ibu ed o he sol en e apo a ion
condi ions. Rega ding he ilms con aining 1.0 w .% MWCNTs, a good ille dispe sion
is obse ed oge he wi h a good compa ibili y (p ope we ing wi h no oids a ound
he ille s) be ween he polyme ic ma ix and he nano ille (whi e a ows in Figu e 1).
Inc easing he amoun o MWCNTs om 1.0 o 3.0 w .% leads o he p esence o small
clus e s and agglome a es. Fu he mo e, he samples a e less compac , showing a ma ked
p esence o oids, pa icula ly in he c oss-sec ion images. Finally, he samples wi h
7.0 w .% MWCNTs con en show a la ge amoun o well-dis ibu ed clus e s along he
samples (su ace and c oss-sec ion images). The dis ibu ion o MWCNTs wi hin he
ma ix a ec s bo h he elec ical and mechanical p ope ies, as clus e s and agglome a es
end o bols e he elec ical p ope ies o he ma e ial mo e e ec i ely han indi idual
Polyme s 2024,16, 1948 6 o 13
MWCNTs [
37
]. Howe e , i is impo an o no e ha hey o en ha e a nega i e impac on
he mechanical p ope ies [38], as will be discussed la e .
Polyme s 2024, 16, x FOR PEER REVIEW 6 o 13
p esence o oids, pa icula ly in he c oss-sec ion images. Finally, he samples wi h 7.0
w .% MWCNTs con en show a la ge amoun o well-dis ibu ed clus e s along he sam-
ples (su ace and c oss-sec ion images). The dis ibu ion o MWCNTs wi hin he ma ix
affec s bo h he elec ical and mechanical p ope ies, as clus e s and agglome a es end o
bols e he elec ical p ope ies o he ma e ial mo e effec i ely han indi idual MWCNTs
[37]. Howe e , i is impo an o no e ha hey o en ha e a nega i e impac on he me-
chanical p ope ies [38], as will be discussed la e .
Figu e 1. Su ace (abo e) and c oss-sec ion (below) SEM images o PCC ma ix and MWCNTs a
1.0 w .% (le ), 3.0 w .% (middle), and 7.0 w .% ( igh ) ille con en . Whi e a ows poin owa ds
he MWCNTs, and clus e s and agglome a es a e dispe sed wi hin he ma ix.
The ib a ion spec a o he polyme and polyme composi es and possible polyme –
ille in e ac ions we e examined by analyzing he cha ac e is ic bands in he in a ed
spec a p esen ed in Figu e 2. In he case o p is ine PCC, he main cha ac e is ic band is
obse ed a 1735 cm−1, which co esponds o he ca bonyl (C=O) s e ching ib a ion. In
addi ion, o he bands ela ed o he PC backbone a e obse ed in he spec a: a 2945 cm−1,
he C-H symme ic s e ching ib a ion, a 1158 cm−1, he C-O-C asymme ic s e ching
ib a ion, and a 1015 cm−1, he symme ic O-C-O s e ching [23]. Rega ding he
PCC/MWCNT composi es, no signi ican band shi s a e obse ed, indica ing he absence
o chemical in e ac ions be ween he polyme and he ille [39,40].
Figu e 2. In a ed spec a o p is ine PCC and PCC/MWCNT composi es wi h diffe en MWCNT
con en s.
Figu e 1. Su ace (abo e) and c oss-sec ion (below) SEM images o PCC ma ix and MWCNTs a
1.0 w .% (le ), 3.0 w .% (middle), and 7.0 w .% ( igh ) ille con en . Whi e a ows poin owa ds he
MWCNTs, and clus e s and agglome a es a e dispe sed wi hin he ma ix.
The ib a ion spec a o he polyme and polyme composi es and possible polyme –
ille in e ac ions we e examined by analyzing he cha ac e is ic bands in he in a ed
spec a p esen ed in Figu e 2. In he case o p is ine PCC, he main cha ac e is ic band is
obse ed a 1735 cm
−1
, which co esponds o he ca bonyl (C=O) s e ching ib a ion. In
addi ion, o he bands ela ed o he PC backbone a e obse ed in he spec a: a
2945 cm−1
,
he C-H symme ic s e ching ib a ion, a 1158 cm
−1
, he C-O-C asymme ic s e ch-
ing ib a ion, and a 1015 cm
−1
, he symme ic O-C-O s e ching [
23
]. Rega ding he
PCC/MWCNT composi es, no signi ican band shi s a e obse ed, indica ing he absence
o chemical in e ac ions be ween he polyme and he ille [39,40].
Polyme s 2024, 16, x FOR PEER REVIEW 6 o 13
p esence o oids, pa icula ly in he c oss-sec ion images. Finally, he samples wi h 7.0
w .% MWCNTs con en show a la ge amoun o well-dis ibu ed clus e s along he sam-
ples (su ace and c oss-sec ion images). The dis ibu ion o MWCNTs wi hin he ma ix
affec s bo h he elec ical and mechanical p ope ies, as clus e s and agglome a es end o
bols e he elec ical p ope ies o he ma e ial mo e effec i ely han indi idual MWCNTs
[37]. Howe e , i is impo an o no e ha hey o en ha e a nega i e impac on he me-
chanical p ope ies [38], as will be discussed la e .
Figu e 1. Su ace (abo e) and c oss-sec ion (below) SEM images o PCC ma ix and MWCNTs a
1.0 w .% (le ), 3.0 w .% (middle), and 7.0 w .% ( igh ) ille con en . Whi e a ows poin owa ds
he MWCNTs, and clus e s and agglome a es a e dispe sed wi hin he ma ix.
The ib a ion spec a o he polyme and polyme composi es and possible polyme –
ille in e ac ions we e examined by analyzing he cha ac e is ic bands in he in a ed
spec a p esen ed in Figu e 2. In he case o p is ine PCC, he main cha ac e is ic band is
obse ed a 1735 cm−1, which co esponds o he ca bonyl (C=O) s e ching ib a ion. In
addi ion, o he bands ela ed o he PC backbone a e obse ed in he spec a: a 2945 cm−1,
he C-H symme ic s e ching ib a ion, a 1158 cm−1, he C-O-C asymme ic s e ching
ib a ion, and a 1015 cm−1, he symme ic O-C-O s e ching [23]. Rega ding he
PCC/MWCNT composi es, no signi ican band shi s a e obse ed, indica ing he absence
o chemical in e ac ions be ween he polyme and he ille [39,40].
Figu e 2. In a ed spec a o p is ine PCC and PCC/MWCNT composi es wi h diffe en MWCNT
con en s.
Figu e 2. In a ed spec a o p is ine PCC and PCC/MWCNT composi es wi h di e en MWCNT
con en s.
3.2. The mal Analysis
The he mal beha io o PCC and composi es is shown in Figu e 3a up o 600
◦
C. The
p is ine polyme displays a single deg ada ion s ep, associa ed wi h he py olysis o PCC
ca bona e g oups [
41
]. Composi es, alike he p is ine sample, only depic one deg ada ion
s ep. A e deg ada ion, a small amoun o esidual weigh is le , which inc eases linea ly
wi h he numbe o nano ubes added o he sample.
Polyme s 2024,16, 1948 7 o 13
Polyme s 2024, 16, x FOR PEER REVIEW 7 o 13
3.2. The mal Analysis
The he mal beha io o PCC and composi es is shown in Figu e 3a up o 600 °C. The
p is ine polyme displays a single deg ada ion s ep, associa ed wi h he py olysis o PCC
ca bona e g oups [41]. Composi es, alike he p is ine sample, only depic one deg ada ion
s ep. A e deg ada ion, a small amoun o esidual weigh is le , which inc eases linea ly
wi h he numbe o nano ubes added o he sample.
The mal s abili y has been s udied based on he i s de i a i e o he TGA cu es, as
shown in Figu e 3b. Maximum deg ada ion empe a u e (T
dmax
) has been collec ed in Ta-
ble 1. The polyme ic ma ix displays a he mal deg ada ion empe a u e o 284.6 ± 9.3 °C,
which does no suffe signi ican a ia ions as a unc ion o ille con en , being he ob-
se ed a ia ions wi hin expe imen al e o .
The DSC esul s, depic ed in Figu e 3c,d, e eal a single he mal ansi ion ha is
ela ed o he glass ansi ion empe a u e (T
g
) o he polyme . The glass ansi ion em-
pe a u es a which he p ocess s a s (T
g-onse
) and inishes (T
g-offse
) a e lis ed in Table 1. The
T
g-onse
alues ange om 110 o 112 °C, whe eas he T
g-offse
alues a e be ween 117 and 120
°C. All in all, hese indings ag ee wi h p e ious he mal esul s, as hey show ha he e
is no a signi ican a ia ion in he measu ed he mal cha ac e is ics o he samples due o
he addi ion o he nano ille s [42]. The empe a u es o he main he mal e en s a e col-
lec ed in Table 1.
Figu e 3. The mal measu emen s o he blank sample and co esponding composi es: (a) TGA
cu es, (b) he i s de i a i es, (c) DSC measu emen s, and (d) magni ica ion be ween 70 and 150
°C empe a u e ange o emphasize he T
g
.
Figu e 3. The mal measu emen s o he blank sample and co esponding composi es: (a) TGA
cu es, (b) he i s de i a i es, (c) DSC measu emen s, and (d) magni ica ion be ween 70 and 150
◦
C
empe a u e ange o emphasize he Tg.
The mal s abili y has been s udied based on he i s de i a i e o he TGA cu es,
as shown in Figu e 3b. Maximum deg ada ion empe a u e (T
dmax
) has been collec ed in
Table 1.
The polyme ic ma ix displays a he mal deg ada ion empe a u e o
284.6 ±9.3 ◦C
,
which does no su e signi ican a ia ions as a unc ion o ille con en , being he obse ed
a ia ions wi hin expe imen al e o .
Table 1. Summa y o he empe a u es o he main he mal e en s. T
dmax
a e ob ained om TGA
expe imen s, whe eas Tg alues a e ob ained om DSC.
w .% MWCNT
Con en
TGA DSC
Tdmax Tg-onse (◦C) Tg-o se (◦C)
0 284.6 ±9.3 111.2 118.3
0.5 279.4 ±8.8 111.9 119.0
1.0 287.3 ±5.9 112.1 118.6
1.5 286.3 ±5.9 110.2 118.1
3.0 291.1 ±7.8 111.3 117.4
5.0 286.5 ±4.9 112.3 117.5
7.0 286.9 ±6.3 111.7 120.0
Polyme s 2024,16, 1948 8 o 13
The DSC esul s, depic ed in Figu e 3c,d, e eal a single he mal ansi ion ha is
ela ed o he glass ansi ion empe a u e (T
g
) o he polyme . The glass ansi ion em-
pe a u es a which he p ocess s a s (T
g-onse
) and inishes (T
g-o se
) a e lis ed in Table 1.
The T
g-onse
alues ange om 110 o 112
◦
C, whe eas he T
g-o se
alues a e be ween 117
and 120
◦
C. All in all, hese indings ag ee wi h p e ious he mal esul s, as hey show ha
he e is no a signi ican a ia ion in he measu ed he mal cha ac e is ics o he samples
due o he addi ion o he nano ille s [
42
]. The empe a u es o he main he mal e en s a e
collec ed in Table 1.
3.3. Mechanical P ope ies
Mechanical p ope ies we e cha ac e ized by s ess–s ain expe imen s in he ensile
mode (Figu e 4a). These mechanical cu es p o ide key pa ame e s, including he ini ial
modulus (E), as well as maximum s ain and s ess. Figu e 4b shows he calcula ed ini ial
modulus. The p is ine PCC exhibi s a alue o EPCC = 1.16
±
0.11 GPa. An inc ease in
he amoun o nano ille leads o a highe ini ial modulus compa ed o he p is ine PCC
sample. This endency is obse ed o nano ille pe cen ages up o 1.0 w .% MWCNTs
(E1.0% = 1.62
±
0.37 GPa), bu inc easing he amoun o ille om 1.5 w .% o 7.0 w .%
dec eases he ini ial modulus.
Polyme s 2024, 16, x FOR PEER REVIEW 8 o 13
Table 1. Summa y o he empe a u es o he main he mal e en s. T
dmax
a e ob ained om TGA
expe imen s, whe eas T
g
alues a e ob ained om DSC.
w .% MWCNT Con en TGA DSC
T
dmax
T
g
-
onse
(°C) T
g
-
offse
(°C)
0 284.6 ± 9.3 111.2 118.3
0.5 279.4 ± 8.8 111.9 119.0
1.0 287.3 ± 5.9 112.1 118.6
1.5 286.3 ± 5.9 110.2 118.1
3.0 291.1 ± 7.8 111.3 117.4
5.0 286.5 ± 4.9 112.3 117.5
7.0 286.9 ± 6.3 111.7 120.0
3.3. Mechanical P ope ies
Mechanical p ope ies we e cha ac e ized by s ess–s ain expe imen s in he ensile
mode (Figu e 4a). These mechanical cu es p o ide key pa ame e s, including he ini ial
modulus (E), as well as maximum s ain and s ess. Figu e 4b shows he calcula ed ini ial
modulus. The p is ine PCC exhibi s a alue o EPCC = 1.16 ± 0.11 GPa. An inc ease in he
amoun o nano ille leads o a highe ini ial modulus compa ed o he p is ine PCC sam-
ple. This endency is obse ed o nano ille pe cen ages up o 1.0 w . % MWCNTs (E1.0%
= 1.62 ± 0.37 GPa), bu inc easing he amoun o ille om 1.5 w .% o 7.0 w . % dec eases
he ini ial modulus.
This beha io can be a ibu ed o in e ac ions be ween he MWCNTs, which lead o
agglome a es and clus e s, as well as o an inc easing p esence o oids in he ilms [37,43].
A low ille concen a ions, he MWCNTs do no agglome a e, and he samples a e mo e
compac . Howe e , as he amoun o MWCNTs inc eases, agglome a ion becomes mo e
p onounced, educing he in e ac ions be ween he polyme and he ille . Fu he mo e,
he s uc u es a e less compac and, he e o e, mo e p one o de o ma ion a lowe s ess.
In addi ion o his, maximum s ess and s ain a b eak alues (Figu e 4b) we e also de-
e mined. The maximum s ess alue dec eases signi ican ly wi h he inclusion o
MWCNTs due o he men ioned agglome a ion effec . Maximum s ain alues a e as-
c ibed o he b i leness o he composi e.
Figu e 4. (a) Rep esen a i e mechanical s ess–s ain cha ac e is ic cu es o he diffe en samples.
(b) Calcula ed ini ial modulus, maximum s ain, and s ess pa ame e s.
3.4. Elec ical P ope ies
F om he ela ion be ween he elec ical conduc i i y and ille pe cen age, he pe -
cola ion h eshold (P
c
) is calcula ed. This h eshold p o ides he concen a ion a which a
signi ican change in he elec ical conduc i i y is obse ed, o in o he wo ds, he concen-
a ion a which he ma e ial changes i s p ope ies om dielec ic o conduc i e. The P
c
Figu e 4. (a) Rep esen a i e mechanical s ess–s ain cha ac e is ic cu es o he di e en samples.
(b) Calcula ed ini ial modulus, maximum s ain, and s ess pa ame e s.
This beha io can be a ibu ed o in e ac ions be ween he MWCNTs, which lead o
agglome a es and clus e s, as well as o an inc easing p esence o oids in he ilms [
37
,
43
].
A low ille concen a ions, he MWCNTs do no agglome a e, and he samples a e mo e
compac . Howe e , as he amoun o MWCNTs inc eases, agglome a ion becomes mo e
p onounced, educing he in e ac ions be ween he polyme and he ille . Fu he mo e,
he s uc u es a e less compac and, he e o e, mo e p one o de o ma ion a lowe s ess.
In addi ion o his, maximum s ess and s ain a b eak alues (Figu e 4b) we e also
de e mined. The maximum s ess alue dec eases signi ican ly wi h he inclusion o
MWCNTs due o he men ioned agglome a ion e ec . Maximum s ain alues a e asc ibed
o he b i leness o he composi e.
3.4. Elec ical P ope ies
F om he ela ion be ween he elec ical conduc i i y and ille pe cen age, he pe co-
la ion h eshold (P
c
) is calcula ed. This h eshold p o ides he concen a ion a which a
signi ican change in he elec ical conduc i i y is obse ed, o in o he wo ds, he concen-
a ion a which he ma e ial changes i s p ope ies om dielec ic o conduc i e. The P
c
indeed depends on he in insic conduc i i y o he ille , i s geome y, and i s dimensional
aspec a io, among o he pa ame e s [
44
]. Fo example, PC/CNT composi es p epa ed by
he sc ew ex ude me hod display P
c
alues o 0.125 w .% [
45
]. Mo eo e , lowe P
c
alues
ha e been ob ained o composi es p ocessed by he sol en cas ing me hod
(0.06 w .%) [42]
and PC/PP blends p epa ed by he mel me hod (0.05 w .%) [46].
Polyme s 2024,16, 1948 9 o 13
Elec ical p ope ies we e de e mined by cu en – ol age (I–V) measu emen , as dis-
played in Figu e 5a. Elec ical conduc i i y was calcula ed using Equa ion (1). The ob ained
alues as a unc ion o he ille con en a e shown in Figu e 5b. A maximum elec ical
conduc i i y o 0.107 S
·
m
−1
was measu ed o he composi e con aining 1.5 w .% MWCNTs.
The pe cola ion h eshold o he samples was calcula ed ollowing Equa ion (3), whe e
σ
is
he composi e’s elec ical conduc i i y,
σ0
is he ille in insic conduc i i y, P is he ille
concen a ion, P
c
is he pe cola ion h eshold, and is he dimensionali y o he conduc i e
ne wo k, being 1 < < 1.3 o a 2D ne wo k and 1.5 < < 2 o a 3D ne wo k [47,48].
σ=σ0(P−Pc) (3)
Polyme s 2024, 16, x FOR PEER REVIEW 9 o 13
indeed depends on he in insic conduc i i y o he ille , i s geome y, and i s dimen-
sional aspec a io, among o he pa ame e s [44]. Fo example, PC/CNT composi es p e-
pa ed by he sc ew ex ude me hod display P
c
alues o 0.125 w . % [45]. Mo eo e , lowe
P
c
alues ha e been ob ained o composi es p ocessed by he sol en cas ing me hod (0.06
w . %) [42] and PC/PP blends p epa ed by he mel me hod (0.05 w . %) [46].
Elec ical p ope ies we e de e mined by cu en – ol age (I-V) measu emen , as dis-
played in Figu e 5a. Elec ical conduc i i y was calcula ed using Equa ion (1). The ob-
ained alues as a unc ion o he ille con en a e shown in Figu e 5b. A maximum elec-
ical conduc i i y o 0.107 S·m
−1
was measu ed o he composi e con aining 1.5 w . %
MWCNTs. The pe cola ion h eshold o he samples was calcula ed ollowing Equa ion
(3), whe e 𝜎 is he composi e’s elec ical conduc i i y, 𝜎 is he ille in insic conduc i -
i y, P is he ille concen a ion, P
c
is he pe cola ion h eshold, and is he dimensionali y
o he conduc i e ne wo k, being 1 < < 1.3 o a 2D ne wo k and 1.5 < < 2 o a 3D
ne wo k [47,48].
𝜎=𝜎
𝑃 𝑃
(3)
The P
c
and pa ame e s a e i ed in Figu e 5b. In he equa ion, P is he w .% o
MWCNTs. The bes i is ob ained wi h P
c
= 0.1 w . % and = 1.15 wi h R
2
= 0.97. The
exponen ial pa ame e is compa ible wi h he o ma ion o a wo-dimensional conduc-
i e ne wo k [42].
Figu e 5. (a) Conduc i i y measu emen s based on cu en – ol age (I–V) cu es; (b) elec ical con-
duc i i y as a unc ion o ille con en . In black a e he conduc i i y alues ob ained om he I-V
cu es and in ed is he i ing based on he calcula ed P
c
and alues.
3.5. The mo esis i e P ope ies
The use o CO
2
-de i ed PC/MWCNT composi es as senso s could con ibu e o e-
ducing he CO
2
oo p in . While nume ous publica ions ha e add essed PC/CNT compo-
si es as s ain senso s, he e is a sca ci y o s udies in he li e a u e conce ning hei appli-
ca ion as empe a u e senso s. Thus, his wo k s udies he he mo esis i e esponse (i.e.,
he change in elec ical esis ance (ΔR) as a unc ion o empe a u e a ia ion (ΔT)) [49] o
CO
2
-PC/MWCNTs o empe a u e senso applica ions.
In o de o de elop such a senso , he composi e equi es a sui able elec ical conduc-
i i y and, he e o e, concen a ions o nano ille s ha exceed he P
c
we e selec ed. Con-
sequen ly, he he mo esis i e measu emen s we e ca ied ou using a conduc i e sample
con aining 3.0 w .% MWCNTs. The he mo esis i e p ope ies we e e alua ed in wo em-
pe a u e egimes: om 30 o 45 °C, sui able o wea ables and human body a ia ions,
and om 40 o 100 °C, o elec onic de ices, espec i ely. Bo h empe a u e anges a e
depic ed in Figu e 6a, displaying an excellen co ela ion be ween esis ance and empe -
a u e a ia ions, al hough some mino elec onic noise is no iceable mainly a lowe em-
pe a u es. E en hough he esis ance changes a e modes (app oxima ely 1 and 2.5 Ω o
Figu e 5. (a) Conduc i i y measu emen s based on cu en – ol age (I–V) cu es; (b) elec ical
conduc i i y as a unc ion o ille con en . In black a e he conduc i i y alues ob ained om he I-V
cu es and in ed is he i ing based on he calcula ed Pcand alues.
The P
c
and pa ame e s a e i ed in Figu e 5b. In he equa ion, P is he w .% o
MWCNTs. The bes i is ob ained wi h P
c
= 0.1 w .% and = 1.15 wi h R
2
= 0.97. The
exponen ial pa ame e is compa ible wi h he o ma ion o a wo-dimensional conduc i e
ne wo k [42].
3.5. The mo esis i e P ope ies
The use o CO
2
-de i ed PC/MWCNT composi es as senso s could con ibu e o educ-
ing he CO
2
oo p in . While nume ous publica ions ha e add essed PC/CNT composi es
as s ain senso s, he e is a sca ci y o s udies in he li e a u e conce ning hei applica ion
as empe a u e senso s. Thus, his wo k s udies he he mo esis i e esponse (i.e., he
change in elec ical esis ance (
∆
R) as a unc ion o empe a u e a ia ion (
∆
T)) [
49
] o
CO2-PC/MWCNTs o empe a u e senso applica ions.
In o de o de elop such a senso , he composi e equi es a sui able elec ical con-
duc i i y and, he e o e, concen a ions o nano ille s ha exceed he P
c
we e selec ed.
Consequen ly, he he mo esis i e measu emen s we e ca ied ou using a conduc i e
sample con aining 3.0 w .% MWCNTs. The he mo esis i e p ope ies we e e alua ed
in wo empe a u e egimes: om 30 o 45
◦
C, sui able o wea ables and human body
a ia ions, and om 40 o 100
◦
C, o elec onic de ices, espec i ely. Bo h empe a u e
anges a e depic ed in Figu e 6a, displaying an excellen co ela ion be ween esis ance and
empe a u e a ia ions, al hough some mino elec onic noise is no iceable mainly a lowe
empe a u es. E en hough he esis ance changes a e modes (app oxima ely 1 and 2.5
Ω
o
∆
T o 15 and 60
◦
C, espec i ely), hey ollow he empe a u e p o iles in bo h cases and
a e sui able o elec onic eadou sys ems.
