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Highly aniso opic conduc i i y o able s p essed om polyaniline /
mon mo illoni e nanocomposi e
J. Toka ský1,2,*, L. Kulhánko á3, L. Neuwi ho á1, K. Mamulo á Ku láko á1, S. Vallo á3, V.
S ýskala4, P. Čapko á5
1 Nano echnology cen e, VŠB-TU Os a a, 17. lis opadu 15/2172, 708 33 Os a a-Po uba, Czech Republic
2 IT4Inno a ions Cen e o Excellence, VŠB-TU Os a a, 17. lis opadu 15/2172, 708 33 Os a a-Po uba, Czech
Republic
3 Facul y o Me allu gy and Ma e ials Enginee ing, VŠB-TU Os a a, 17. lis opadu 15/2172, 708 33 Os a a-
Po uba, Czech Republic
4 Facul y o Elec ical Enginee ing and Compu e Science, VŠB-TU Os a a, 17. lis opadu 15/2172, 708 33
Os a a-Po uba, Czech Republic
5 Facul y o Science, Uni e si y o J. E. Pu kyně, České mládeže 8, 400 96 Ús í nad Labem, Czech Republic
Abs ac
Polyaniline/mon mo illoni e nanocomposi e was p epa ed om anilinium sul a e (p ecu so ) and
ammonium pe oxodisul a e (oxidizing agen ) using simple one-s ep me hod. The esul ing
nanocomposi e ob ained in powde o m has been p essed in o able s using a ious comp ession
p essu es (28-400 MPa). Elec ical conduc i i ies o able s in wo pe pendicula di ec ions, i.e.
di ec ion pa allel wi h he main su ace o able (σ=) and in o hogonal di ec ion (σ┴), and
co esponding aniso opy ac o s (i.e., he a io σ= /σ┴) ha e been s udied in dependence on
comp ession p essu e used du ing he p epa a ion. Polyaniline/mon mo illoni e nanocomposi e was
cha ac e ized using X- ay di ac ion analysis, Raman spec oscopy, ansmission elec on
mic oscopy, he mog a ime ic analysis and molecula modeling which led o he unde s anding o he
in e nal s uc u e. Measu emen o ha dness pe o med on p essed able s has been also in ol ed.
Taking in o accoun he highes alue o aniso opy ac o eached (σ= /σ┴ = 490), p esen s udy shows
a chance o design conduc o s wi h nea ly wo-dimensional conduc i i y.
Keywo ds: composi es, laye ed compounds, chemical syn hesis, high p essu e, elec ical
p ope ies
* Co esponding au ho a Nano echnology Cen e, VŠB – Technical Uni e si y o Os a a, 17. lis opadu 15,
70833 Os a a, Czech Republic. E-mail add ess: jonas. oka sky@ sb.cz
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1. In oduc ion
In conduc ing polyme sys ems he nanos uc u e and chains alignmen a e he c ucial ac o s
a ec ing hei p ope ies. O de ing o polyme chains can be achie ed by a ious me hods
such as mechanical o ien a ion o polyaniline (PANI) chains using blends wi h insula ing
polyme s, using elec ic ield o high p essu e [1-3]. Hyb id PANI/phyllosilica e
nanocomposi es o e he p omising way o PANI chains alignmen due o he inclusion o
phyllosilica e pa icles in o polyme ic ma ix and due o he in e cala ion o polyme ic chains
in o he phyllosilica e laye ed s uc u e. In addi ion, he in e ac ion o PANI chains wi h
phyllosilica e s uc u e leads o imp o ed he mal, mechanical and an ico osi e p ope ies [4-
6]. Among a ious phyllosilica es he mon mo illoni e (MMT) ep esen s he mos con enien
laye ed s uc u e sui able as a ma ix o conduc ing polyme s because (1) MMT s uc u e is
easily expandable (i.e., able o accommoda e polyme ic chains in he in e laye space) and (2)
hanks o a low laye cha ge o MMT laye s he conduc i i y o PANI chains is no
signi ican ly educed in PANI/MMT nanocomposi e.
Dependence o conduc i i y on p essu e o PANI and i s de i a i es has been in es iga ed by
se e al au ho s [7-9]. Resul s ob ained in hese s udies showed ha he dependence can be
s ongly a ec ed by many ac o s, like acid doping o PANI, he syn hesis pa hway, and use
o PANI de i a i es. In spi e o many s udies ocused on conduc i i y o PANI/phyllosilica e
nanocomposi es [4-6,10-15], he dependence o conduc i i y on comp ession p essu e used
o he p epa a ion o able s om hese ma e ials has no been s udied ye . In p esen wo k
we in es iga e how a ious comp ession p essu es (28-400 MPa) a ec he elec ical
conduc i i y o able s p epa ed om PANI/MMT nanocomposi e. Also, he in e nal s uc u e
o PANI/MMT nanocomposi e is s udied using combina ion o X- ay di ac ion analysis,
he mog a ime ic analysis, ansmission elec on mic oscopy, Raman spec oscopy, and
molecula modeling. The main aim o ou wo k is eaching e y high aniso opy in o de o
ob ain he wo-dimensional conduc i i y.
2. Expe imen al
2.1. P epa a ion o he samples
Aniline, sul u ic acid and ammonium pe oxodisul a e we e pu chased om he Lach-Ne
company (Czech Republic) and used as ecei ed. Comme cially a ailable Na-MMT
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Po aclay® (The mine al company Anke poo NV, Ne he land) ha ing s uc u al o mula
(Si8) (Al2.85Mg0.71Ti0.02Fe3+0.42) O20 (OH)4 wi h laye cha ge ~ 0.7 el. pe uni cell was used o
p epa e PANI/MMT composi es. Po aclay® is a ligh g ay ine powde ha ing, acco ding o
he in o ma ions p o ided by he supplie , ela i e densi y 2.6 and pH o 5% solu ion in wa e
a 20 °C in he ange 9 – 10. Size ac ion ˂ 40 μm was used du ing o p epa a ion o he
samples. Speci ic su ace a ea calcula ed om BET iso he m is 31 m2·g-1.
Pu e PANI powde was p epa ed by oxida i e polyme iza ion o he solu ion o aniline by
ammonium pe oxodisul a e in acidic en i onmen (sul u ic acid). Time o he polyme iza ion
was 60 minu es (da k g een colo indica ing he o ma ion o eme aldine sal was obse ed).
The g een solid was collec ed on a il e by insing wi h dis illed wa e and d ied a 40 °C in a
kiln.
PANI/MMT composi es we e p epa ed using one-s ep p ocess. The anilinium sul a e and
ammonium pe oxodisul a e we e added in o wa e suspension o MMT. Polyme iza ion o
aniline was comple ed a e 60 minu es, bu he suspension was s i ed o 6 hou s o ensu e
ha he la ges possible amoun o PANI en e s he in e laye space o MMT. The g een solid
was also collec ed on a il e by insing wi h dis illed wa e and d ied a he same condi ions
as pu e PANI.
P epa ed PANI and PANI/MMT powde s (3 g o powde o each able ) we e p essed in o
squa e able s using ZWICK 1494 p ess (applied p essu es 28, 50, 100, 200, 300, and 400
MPa) a oom empe a u e, wi hou any lub ica ion and binde . Pa ame e s o he con olled
p essing we e as ollows. Loading speed was 1.0 mm·min-1 and using inal p essu e he
sample was compac ed o 10 minu es. Unloading speed was 0.1 mm·min-1. Size o each
squa e able was 28×28 mm.
2.2. Cha ac e iza ion me hods
2.2.1. X- ay powde di ac ion
X- ay di ac ion (XRD) measu emen s ha e been ca ied ou in o de o cha ac e ize he
deg ee o p e e ed o ien a ion o MMT la pa icles in PANI/MMT nanocomposi e samples.
The XRD pa e ns we e eco ded unde CoKα i adia ion (λ = 1.789 Å) using he B uke D8
Ad ance di ac ome e (B uke AXS) equipped wi h a VÅNTEC 1 de ec o .
2.2.2 T ansmission elec on mic oscopy
PANI and PANI/MMT samples in powde o m we e dispe sed in wa e and ul asonica ed
o 5 minu es. One d op om each dispe sion was placed on he Cu mesh co e ed by ca bon
memb ane and bo h samples we e d ied a oom empe a u e. The mo phology o samples
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was obse ed on a a ansmission elec on mic oscope (TEM) JEOL 2010 HC (JEOL L d.,
Japan). Accele a ing ol age was 160 kV.
2.2.3. The mog a ime y analysis
Simul aneous he mog a ime e -di e en ial scanning calo ime e (TG-DSC) STA 409 EP
(Ne zsch) equipped wi h a high-sensi i e analy ical balance was used o measu ing he mass
change o he samples (30 mg in weigh ) as a unc ion o ime o empe a u e. The sample
ca ie sys em con ains he ype S he mocouples (P 10%Rh-P ) o measu e he empe a u e
and he empe a u e di e ence. All samples we e hea ed up o 1000 °C in he c ucibles (α-
Al2O3) in a dynamic a mosphe e o d y ai wi h a low a e o 100 cm3∙min-1. Hea ing a e was
10 °C∙min-1.
2.2.4. Ha dness measu emen
To compa e mechanical p ope ies o PANI and PANI/MMT composi es he inden a ion
ha dness (HIT) was measu ed using Zwick ZHU 2.5, whe eas 5 mm s eel ball was used as an
inden o .
2.2.5. DC conduc i i y measu emen
Special measu ing cell was cons uc ed o measu emen o DC conduc i i y (see
Supplemen a y ma e ial, Fig. S1a). A ached DC ol age sou ce (DC POWER SUPPLY HY
3003 D-2) was s abilized wi h a ole ance o 10-3 (i.e. he p ecision was 2.000 ± 0.001 V) and
annexed wi h he endu ance o se e al ens o seconds o minu es. G ea a en ion was paid o
ix he con ac a ea o he sample wi h la Cu elec odes. These elec odes we e polished
be o e each measu emen using a special ab asi e pas e. Elec ic cu en passing h ough he
sample has been measu ed in wo pe pendicula di ec ions, in he able plane and in
o hogonal di ec ion o he able plane (see Supplemen a y ma e ial, Fig. S1b), and he mean
alue o elec ic cu en was used o calcula e he conduc i i y. Mul ime e AGILENT
34401A and V-me e UNI-T UT802 we e used o he calib a ion. All pa ame e s necessa y
o he measu emen we e speci ied and con olled using compu e equipped wi h PCI-6221
boa d. Da a we e egis e ed and p ocessed in he homemade so wa e p epa ed in LabVIEW
en i onmen .
2.2.6. Molecula modeling
Molecula modeling was ca ied ou in Ma e ials S udio modeling en i onmen (MS). The
MMT c ys al s uc u e was buil using he s uc u e da a published by Mé ing and Obe lin
[16] and Tsipu sky and D i s [17]. The model o MMT subs a e was buil unde pe iodic
bounda y condi ions as a supe cell wi h he o mula (Al46 Mg16 Fe3+10) (Si144) O360 (OH)72 and
wi h he o al nega i e laye cha ge -16 el. This cha ge, a ising om he subs i u ions in
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oc ahed a, was compensa ed by Na+ ca ions and/o PANI chains (p epa ed as dime s wi h
cha ge +4 el.) in he in e laye space. Se o ini ial models wi h i e di e en Na+/PANI a ios
(8/0, 6/1, 4/2, 2/3, 0/4) and a ious numbe s o wa e molecules was p epa ed. A omic
cha ges in MMT s uc u e we e assigned using he cha ge equilib a ion (QEq) me hod
allowing p edic ion o cha ge dis ibu ions based on a omic ioniza ion po en ials, elec on
a ini ies and a omic adii [18] while o cha ges o PANI and wa e molecules he Gas eige
me hod was used [19]. All models ha e been op imized using Uni e sal o ce ield able o
pa ame e ize a oms bo h in o ganic (PANI) and ino ganic (MMT) pa o he s uc u e [20]. A
Sma algo i hm was used o he geome y op imiza ion wi h 500 000 i e a ion s eps.
In e laye dis ance o each model op imized in MS/Fo ci e module has been calcula ed using
MS/Re lex module unde he same condi ions as in he expe imen (i.e., 2θ ange: 5-50°; CoKα
i adia ion (λ = 1.78897 Å), B agg-B en ano geome y) and compa ed wi h expe imen al da a
in o de o ind he mos p obable in e laye s uc u e.
3. Resul s and discussion
3.1. Thickness, dimensional s abili y, homogenei y and ha dness o able s
In dependence on applied p essu es, i.e., 28, 50, 100, 200, 300, and 400 MPa, a ious
hicknesses o able s (d0) we e ob ained (see Supplemen a y ma e ial, Table S1). Wi h
espec o he po ion o powde s (3 g o each able ) and densi ies o PANI (1.46 g·cm-3) and
PANI/MMT (1.99 g·cm-3) measu ed by He pycnome e , heo e ical hicknesses should be 2.6
mm and 1.9 mm, espec i ely. Table S1 shows ha his alues ha e no been eached e en a
a p essu e o 400 MPa. Howe e , he hicknesses d0 measu ed immedia ely a e he
compac ion (d0(PANI) = 2.708 mm, d0(PANI/MMT) = 2.039 mm) a e e y close o hese
alues. Thicknesses we e u he measu ed a e 40 days (see alues d40 in Table S1) in o de
o es ima e he dimensional s abili y o able s.
I is e iden ha PANI/MMT able s ha e highe dimensional s abili y han PANI able s o
p essu es 28-200 MPa. Signi ican expansion o PANI/MMT able s (i.e. highe Δd alues)
can be obse ed only when he p essu e is 300 and 400 MPa.
Leng hs o edges (a0 = 28 mm) did no change signi ican ly du ing 40 days. Di e ences Δa
we e o o de o 1·10-2 % o all able s.
In o de o ind whe he he PANI and MMT a e homogeneously dis ibu ed in p essed
PANI/MMT able s, simple expe imen was pe o med. Each PANI/MMT able was b oken
in o 10 pieces, hese pieces we e weigh ed, calcined a 1000 °C o 3 h, and, inally, he
weigh loss (WL) o each piece o each able was measu ed. No signi ican di e ences
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be ween WL o pieces we e ound o each able and his ac sugges s ha PANI/MMT
able s can be conside ed homogeneous. Fo illus a ion, he WL alues o en pieces o
able comp essed by p essu e o 28 MPa a e p o ided (see Supplemen a y ma e ial, Table
S2). Al hough he WL is sligh ly highe o smalle pieces wi h lowe weigh s, all WL alues
a e e y simila . The a e age WL alue ~ 42 % was ob ained o all PANI/MMT able s.
Compa ison o ha dness o PANI able s and PANI/MMT able s is shown in Fig. 1 and
clea ly demons a es he inc eased ha dness o PANI/MMT composi e. Taking in o accoun
ha inden o can mee ei he PANI o MMT pa icle, he ha dness was measu ed epea edly a
10 di e en poin s on he su ace and he a e age alues a e p esen ed.
Fig. 1. Compa ison o ha dness in dependence on p essu e used o he p epa a ion o PANI
and PANI/MMT able s.
3.2 S uc u e analysis
Visual obse a ions o powde ma e ials we e ca ied ou using TEM. I can be clea ly seen
ha pu e PANI powde (Fig. 2a) is composed om a od-shaped g ains. Leng h and diame e
o g ains is abou 200 nm and 50 nm, espec i ely. Such shaped g ains end o a ange pa allel
o one ano he unde ex e nal p essu e. The o al olume o powde is hus educed and his
seems o be he eason o he signi ican dec ease in hickness o he pu e PANI able s
p essed a high p essu es (see Supplemen a y ma e ial, Table S1). Fig. 2b shows ha
PANI/MMT powde is much mo e dense han pu e PANI powde . MMT laye s can be clea ly
dis inguished as a da k elonga ed bodies bounded and su ounded by PANI.
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Fig. 2. TEM images o (a) pu e PANI, and (b) PANI/MMT powde s. MMT pa icles can be
dis inguished as a da k elonga ed bodies.
XRD pa e n o PANI able s showed he ypical di ac og am o amo phous polyme ic
samples, keeping he same p o ile o he whole p essu e ange 28-400 MPa (see
Supplemen a y ma e ial, Fig. S2). One can see ha he di ac ion pa e ns a e e y noisy and
all peaks a e qui e b oad. On he o he hand, he XRD pa e n o PANI/MMT composi e
able s exhibi s he s ong ex u e (Fig. 3), i.e. he s ong p e e ed o ien a ion o pla y MMT
pa icles wi h hei basal plane 001 pa allel o he main su ace o able (see Supplemen a y
ma e ial, Fig. S3). Inc easing p e e ed o ien a ion o MMT pa icles in dependence on
inc easing p essu e in composi e samples mani es s i sel wi h inc easing in ensi y o 001
di acion line o MMT (Fig. 3).
Fig. 3. X- ay di ac ion p o ile o 001 basal e lec ion o MMT in PANI/MMT composi e,
illus a ing he inc ease o peak in ensi y due o inc ease o p e e ed o ien a ion o MMT
pa icles wi h inc easing p essu e.
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Mo eo e , as one can see in Fig. 3, he p e e ed o ien a ion o MMT pa icles eached
maximum a 300 MPa and inc ease in p essu e does no lead o highe deg ee o o ien a ion.
Di ac ion analysis o 001 peak posi ion also showed he ollowing inc ease o he MMT
in e laye dis ance in PANI/MMT composi e. While he p is ine MMT has he in e laye
dis ance 1.245 nm, in able s p essed om PANI/MMT composi e he in e laye dis ances in
MMT a e ~ 1.295 nm.
Fo PANI/MMT composi es, he expansion o MMT in e laye dis ance is conside ed as an
e idence o in e cala ion o PANI by many au ho s [4,5,13,21,22]. In ou s udy, molecula
modeling was used o suppo he esul s o XRD analysis. Resul s o he modeling showed
ha he alue d001 = 1.295 nm may co espond no only o a ious amoun o PANI chains in
he MMT in e laye space bu also o he MMT in e laye space wi hou PANI i con aining ~
13.4 w .% o wa e (Fig. 4).
Fig. 4. Dependencies o amoun o wa e and PANI in he MMT in e laye space on he d001
alues as calcula ed om he op imized models. Real sample (2.4 w .% o wa e ; d001= 1.295
nm) is displayed as he bold c oss.
Howe e , TG/DTA o PANI/MMT sample (Fig. 5) e ealed ha he amoun o wa e in he
MMT in e laye space is ~ 2.4 w .%. This alue helped us o elimina e all implausible models.
Taking in o accoun all known expe imen al da a (i.e. d001 alue and amoun o in e laye
wa e ) and molecula modeling esul s (Fig. 4) he si ua ion in he eal PANI/MMT sample
seems o be an a e age o model ha ing d001 = 1.296 nm and con aining wo PANI chains (i.e.
9.4 w .% o PANI) and 38 wa e molecules (i.e. 4.4 w .% o H2O) and model d001 = 1.294 nm
and con aining h ee PANI chains (i.e. 14.1 w .% o PANI) and 5 wa e molecules (i.e. 0.6
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w .% o H2O). The e o e, con en o he in e laye space in eal PANI/MMT sample can be
es ima ed a 2.5 w % o wa e and 11.7 w .% o PANI. Molecula modeling also showed ha
Na+ ions in he MMT in e laye space a e no ully exchanged by PANI chains. Taking in o
accoun ha ideally 2.5 PANI chains a e p esen in he MMT in e laye space, only ~ 40 % o
Na+ ions we e exchanged.
Fig. 5. The mal analysis o (a) pu e MMT and (b) PANI/MMT samples.
Amoun o PANI chains in he in e laye space, calcula ed om op imized models, can be
compa ed wi h esul s o TG/DTA (Fig. 5b). While empe a u es up o 200 °C esul s in he
loss o adso bed wa e (endo he mic p ocess wi h maximum a 94.5 °C and weigh loss 6.4
w .%), exo he mic p ocess wi h maximum a 459.1 °C and weigh loss 28.98 w .% is
obse ed in he ange 200-650 °C. This p ocess can be a ibu ed o he gasi ica ion o o ganic
ma e . The expec ed amoun o PANI in he MMT in e laye space (i.e., 11.7 w .%,
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