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Synthetic Metals 160 (2010) 708–712

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Synthetic Metals

journa l homepage: www.e lsev ier .com/ locate /synmet

reparation, FTIR spectroscopic characterization and isothermal stability ofifferently doped conductive fibers based on polyaniline and polyacrylonitrile

sif Ali Khan ∗, Mohd Khalidnalytical and Polymer research Laboratory, Department of Applied Chemistry, Faculty of Engineering & Technology, Aligarh Muslim University, Aligarh-202 002, U.P., India

r t i c l e i n f o

rticle history:eceived 28 April 2009eceived in revised form

a b s t r a c t

Conductive fibers based on polyaniline (PANI) and polyacrylonitrile (PAN) were obtained by stirringwith magnetic bar. This research was conducted to investigate conducting fibers of polyani-line:polyacrylonitrile (PANI:PAN) composite with different weight ratios of aniline in PAN matrix. The

9 December 2009ccepted 5 January 2010vailable online 8 February 2010

eywords:onducting polymerlectrical conductivity

fibers were prepared by stirring process. The best conductivity behavior of the fibers was obtained with5 mL of aniline. The fibers obtained were characterized using Fourier-transform infrared spectra (FTIR),scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The variation of electricalconductivity with different type doping agents (HCl, H2SO4 and HClO4) and the stability in terms of DCelectrical conductivity retention was studied in an oxidative environment by isothermal characteristics.

© 2010 Elsevier B.V. All rights reserved.

hermal stability

. Introduction

Recently [1], we have prepared conducting fibrousolyaniline:nylon-6,6 by stirring aniline and nylon-6,6 solu-ion with the help of magnetic bar, as in this technique theonductivity of the fibrous material depends on the ratio of con-ucting polymer present in fibrous material. It is difficult directlyo form fibers of conducting polymers, stirring process is appliedo form fibers of conducting polyaniline and polyacrylonitrile.lectrically conducting polymers are an important and interestinglass of new organic materials that have gained considerablettention in the recent years. These polymers have been used inany applications including sensors [2,3], switchable membranes

4], anticorrosive coatings [5,6], biosensors [7], electrochromicevices [8] and rechargeable batteries [9,10]. Most of the works, inhis area, are focused on the dynamic reversible redox propertiesf the polymers. One of the most important class ES of conductingolymers that has been studied extensively [11]. Polyanilinean be doped and undoped on exposure to an acidic or alkalinenvironment without changing the number of �-electrons in the

olymer [12]. This mechanism is attributed due to the presence ofNH and –N-groups in the polymer backbone whose protonation

nd deprotonation will bring about a change in the electroniconductivity as well as in the color of the polymer [13]. It is

∗ Corresponding author.E-mail addresses: asifalikhan2008@gmail.com (A.A. Khan),

kansarister@gmail.com (M. Khalid).

379-6779/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.synthmet.2010.01.005

believed that all or some of the nitrogen atoms (amines or imines)in any species can be protonated with protonic acids [14]. Thisaspect of doping and undoping makes polyaniline and its analoghighly suitable for industrial applications.

The electronically conductive polymeric filler can also have astrong effect on the electrical properties (DC conductivity and ACimpedance) of the composite, but only when the fillers are highlyconductive compared to the matrix [15,16]. Long, thin inclusionslike fibers, which are insulating with respect to the matrix, havelittle effect on overall electrical properties [17], although they canaffect mechanical properties. The electrical behavior of the fibersdue to the presence of highly conductive filler is typically dis-cussed with reference to the percolation threshold [18,19]. Whenenough conductive fillers have been added to the matrix, the fibersare above the percolation threshold, which is defined as a char-acteristic volume or number fraction of filler at which continuouspaths for electrical current exist in the composite. Some of thesepaths can occur through parts of the matrix where there has beendielectric breakdown between filler tips, although most of the con-duction is probably through touching fillers. PAN is one of themost important polymers for making fiber as it can be widelyused because of its high strength, high abrasion resistance andgood insect resistance. However, the PAN based conducting fibershave not much being explored. In the present study, the fibers

were made up of insulating polymer (polyacrylonitrile) with con-ducting polymer (polyaniline). These fibers are a new promisingmaterial from two perspectives; first the electrical conductivi-ties are enough for a broad range of applications, secondly theformation of fibers using stirring technique in this study is supe-

A.A. Khan, M. Khalid / Synthetic Metals 160 (2010) 708–712 709

Table 1Preparation details of polyaninline:polyacrylonitrile composite fibers.

Sample ID PAN (g) THF (mL) Amount of aniline in (1 g PAN solution) (mL) Electrical conductivity � (S/cm)

−5

rp

2

2

(Oap

2

isw3tttwildsm0loct

2

rpmmattdpcw

�

G

�

to 100 ◦C with different doping agents viz. HCl, H2SO4 and HClO4(0.1 M). The fibers doped with H2SO4 and HClO4 had lower mag-nitude of conductivity when compared to fibers doped with HCl(Fig. 2).

PANI:PAN-1 1 25 1PANI:PAN-2 1 25 3PANI:PAN-3 1 25 5PANI:PAN-4 1 25 6

ior to chemical synthesis given consideration of time and costarameters.

. Experimental

.1. Reagents and chemicals

The following reagents and chemicals were used: aniline, 99%CDH, India), polyacrylonitrile (from Research, Design and Standardrganization, India), hydrochloric acid, 35% (E. Merk, India), sulfuriccid (Qualigence), perchloric acid (E. Merk, India) and Ammoniumersulphate (CDH, India) and tetrahydrofuran (CDH, India).

.2. Preparation of conducting fibers

Conducting fibers of PANI:PAN composite were prepared in var-ous volume ratios of aniline with polyacrylonitrile solutions bytirring vigorously at room temperature. 1 g of polyacrylonitrileas dissolved in 25 mL of tetrahydrofuran. Different volumes (1 mL,mL, 5 mL and 6 mL) of aniline were added in polyacrylonitrile solu-

ion (Table 1). The solutions were well mixed using the glass rodhen solution was poured drop wise in water with vigorous stirringo prepare the fibers using magnetic stirrer. The prepared fibersere kept in 200 mL of 0.1 M (NH4)2S2O8 solution for overnight

n refrigerator, in order to get oxidative polymerization of ani-ine in the polyacrylonitrile. The fibers were washed with doublyistilled water and acetone and left overnight with 2% ammoniaolution, again washed with doubly distilled water. The resultingaterial is a base free and undoped. The fibers were doped with

.1 M (HCl, H2SO4 and HClO4) acid solutions to convert the polyani-ine emeraldine base into electrically conducting fibers. The pelletsf these fibers were made by using hydraulic pressure (25 kN). DConductivity measurements of the fibers were performed at roomemperature using four in-line probes (DMV 001, Roorke India).

.3. Characterization

The FTIR spectra of polyaniline and conducting fibers wereecorded by a Perkin Elmer 1725 instrument. The SEM studies wereerformed on a LEO-435 VP instrument to examine the surfaceorphology of the fibers and their components. The thermogravi-etric analysis (TGA) were performed on the composite by usingPerkin Elmer (Pyris Dimond) instrument heating from ∼25 ◦C

o 600 ◦C at the rate of 10 ◦C min−1 in nitrogen atmosphere withhe flow rate of 30 mL/min. The DC electrical conductivity of theifferently doped fibers pellet was measured with increasing tem-erature (35–130 ◦C) by using four-in-line probes, DC electricalonductivity measuring instrument. DC electrical conductivity (�)as calculated using the following equations:

= �0

G7(W/S)(1)

7W

S= 2S

Wln 2 (2)

0 = V

I2pS (3)

∼10∼10−3

∼10−1

∼10−1

� = 1�

(4)

G7(W/S) is a correction divisor which is a function of thickness ofthe sample as well as probe-spacing where I, V, W and S are current(A), voltage (V), thickness of the film (cm) and probe-spacing (cm)respectively [20]. The isothermal stability of pellets in terms of DCelectrical conductivity retention was carried out on the selectedsamples at 50 ◦C, 70 ◦C, 90 ◦C, 110 ◦C and 130 ◦C in an air oven.The electrical conductivity measurements were carried out at aninterval of 15 min.

3. Results and discussion

3.1. Electrical properties

The electrical conductivity of the fibers having 1 mL, 3 mL, 5 mLand 6 mL of aniline increases from 10−5 to 10−1 S/cm after dopingthe fibers in hydrochloric acid for 24 h. The effect of aniline con-tent on electrical conductivity of the PANI:PAN composite fibersis plotted in Fig. 1. When the volume fraction of aniline is addedup to 5 mL, the conductivity reached from 10−6 to 10−1 S/cm. Thesaturation in conductivity also reached after loading above 5 mLof aniline. The conductivity increases sharply when the volumeration of aniline is less than 4 mL, after that, it was graduallyreached up to 10−1 S/cm when more aniline was added up to5 mL. It is evident that the percolation of the conductive fibersshould be less than 5 mL of aniline volume. Hence, the thresh-old conductivity was reached by 5 mL of aniline loading. Fibersof PANI:PAN composite with 5 mL aniline has also shown betterconductivity as compared to our previous reported work [21,22].Therefore, the fibers (5 mL of aniline solution) were selected tothe study of temperature dependence of electrical conductivity up

Fig. 1. Electrical conductivity as a function of polyaniline fraction in fibrous polyani-line:polyacrylonitrile.

710 A.A. Khan, M. Khalid / Synthetic Metals 160 (2010) 708–712

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Table 2FTIR peak positions (cm−1) of polyaniline (PANI), polyactylonitrile (PAN) and fibersof polyaniline:polyacrylonitrile composite.

PANI PAN PANI:PAN-1 PANI:PAN-2 PANI:PAN-3

3259 3969 3417 3439 34693035 3652 3251 3239 32802846 3555 2950 3004 30072358 3442 2230 2234 22391587 2950 2049 2049 20481497 2844 1965 1965 19591377 2653 1726 1736 17241302 2598 1603 1580 15801241 2414 1457 1427 14271143 2051 1387 1384 13871008 1995 1145 1267 1266954 1726 1034 1104 1162824 1637 988 1064 1064728 1451 912 985 983505 1387 841 911 913

1069 827 841 841983 810 826 825954 750 810 803912 694 750 751842 618 693 696827 554 583 588810 509 510 510

ig. 2. Conductivity versus HCl, H2SO4 and HClO4 doped composite fibers withncreasing temperature (30–100 ◦C).

.2. FTIR characterization

The interaction between polyaniline and the polyacrylonitrile

atrix was investigated via Fourier-transform infrared spectral

nalysis. The fibers were dried in an oven at 45 ◦C. Fig. 3 shows theTIR spectra of polyaniline, polyacrylonitrile and hydrochloric acidoped fibers and the FTIR values are shown in Table 2. The band

ig. 3. FTIR spectra of (a) PANI, (b) PAN, (c) PANI:PAN-1, (d) PANI:PAN-2 and (e)ANI:PAN-3.

750655524

corresponding to out of plane bending vibration of C–H bond ofp-disubstituted benzene rings appears at 824 cm−1. The bands cor-responding to stretching vibration of N–B–N and N Q N structureswere appeared at 1497 cm−1 and 1587 cm−1 respectively where –Band Q stand for benzenoid and quinoid moieties in the polyani-line. These relative lower frequencies of benzenoid and quinoid ringstretching are due to the salt formation with HCl [23]. The bandscorresponding to vibration mode of N Q N ring and stretchingmode of C–N bond appear at 1143 cm−1 and 1302 cm−1. The FTIRspectrum supports the presence of benzenoid as well as quinoidmoieties in the polyaniline [24]. The characteristic broad band for–CN groups in polyacrylonitrile was appeared around 1995 cm−1.The peaks at 3251 cm−1, 3239 cm−1 and 3280 cm−1 were observedfor PANI:PAN-1, PANI:PAN-2 and PANI:PAN-3 respectively. As theamount of polyaniline increased the intensities of these peakswere also increased. Other characteristic peaks for conductingfibers of PANI:PAN composite were also observed at 2239 cm−1

and 1162 cm−1. Two characteristic bands for CH2 were appearedaround 1451 cm−1 and around 750 cm−1 for the bending and rock-ing vibrations, respectively. In the spectrum a broad band in theregion at 3370 cm−1 may be due to the presence of external watermolecule. While a sharp peak in region at 1644 cm−1 is referred tobanding vibration of water. In the composite, the gradual increasein the intensities of the bands corresponding to PANI and decreasein the band corresponds to PAN support the gradual change inthe composition of the composite formulation as evident fromFig. 3.

3.3. SEM studies

Fig. 4(a and b) shows the photographs of conducting fibers ofPANI:PAN composite and PAN fibers. Fig. 4(c and d) shows theSEM micrographs of fibers pellet and single conducting fiber. Thecross-section SEM micrograph of the conductive fiber containing

5 mL of aniline in PAN solution has been shown in Fig. 4(d) attainssome dark spots and bright grooves. The intensity of groovingbecomes more intense at certain places, where the conductive par-ticles are present in aggregated structure with in the polymericmatrix. The dark region is related to conductive polyaniline phase,

A.A. Khan, M. Khalid / Synthetic Metals 160 (2010) 708–712 711

and d)

wtlmsc

3

adttAo

doped fibers pellet has been maintained at the different tempera-tures temperature. The DC electrical conductivity was measured at

Fig. 4. (a and b) Photographs of (a) fibers of PANI:PAN and (b) PAN fibers. (c

hile the bright region is related to non-conducting polyacryloni-rile phase. It is observed that polyaniline content is markedlyocalized in the polyacrylonitrile matrix. From the above SEM

icrograph, an excellent dispersion between two components iseen in which about 15–20% dark phase of PANI can be observedlearly.

.4. TGA studies

As evident from Fig. 5 the TGA analysis showed that the fibersre stable up to 151 ◦C. At about 272 ◦C, the mass loss begins (∼6%),ue to the loss of water and low molecular weight oligomers. Fur-

her loss of mass started from 301 ◦C to 600 ◦C may be due tohe loss of dopant and degradation/decomposition of the polymer.bove 600 ◦C, the results obtained were associated with the residuenly.

Fig. 5. TGA curve of PANI–PAN composite.

SEM micrographs of (c) pellet of fibers of PANI:PAN and (d) PANI:PAN fiber.

3.5. Isothermal stability in terms of DC electrical conductivityretention

The fibers were observed to show enhanced electrical con-ductivity on exposure to HCl, due to the charge-transfer reactionbetween conducting fibers doping agents, HCl [25,26].

[PANI(PAN)] + nHCl → [(PANI-nH+(PAN)][(nCl−)] (5)

The stability of electrical conductivity under isothermal con-ditions at 50 ◦C, 70 ◦C, 90 ◦C, 110 ◦C and 130 ◦C of the differently

an interval of 15 min in the accelerated ageing experiment show-ing in Figs. 6–8. It has been observed that the electrical conductivityis stable at 50 ◦C, 70 ◦C and 90 ◦C, support the fact that the fibrous

Fig. 6. DC electrical conductivity retention under isothermal conditions at 50 ◦C,70 ◦C, 90 ◦C, 110 ◦C and 130 ◦C of HCl doped fibrous PANI:PAN-3.

712 A.A. Khan, M. Khalid / Synthetic M

Fig. 7. DC electrical conductivity retention under isothermal conditions at 50 ◦C,70 ◦C, 90 ◦C, 110 ◦C and 130 ◦C of H2SO4 doped fibrous PANI:PAN-3.

F7

moia

[[[[[[[[[

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ig. 8. DC electrical conductivity retention under isothermal conditions at 50 ◦C,0 ◦C, 90 ◦C, 110 ◦C and 130 ◦C of HClO4 doped fibrous PANI:PAN-3.

aterials are sufficiently stable under ambient conditions in termsf DC electrical conductivity retention below 90 ◦C. The decreasen electrical conductivity with time of isothermal ageing at 110 ◦Cnd 130 ◦C may be attributed to the loss of dopant and the chem-

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etals 160 (2010) 708–712

ical reaction of dopant with polymer i.e. degradation of polymercomposites.

4. Conclusion

Electrically conductive and isothermally stable conductingfibers of PANI:PAN composite were prepared using by stirring pro-cess. 5 mL volume of aniline contain fibers of differently doped hasbeen performed best. From the above-mentioned studies, it hasbeen concluded that DC conductivity studies of the fibers, stronglydepend on doping types and counter ion of the dopant which has aneffective control on the mechanism of electrical conductivities offibers. The conducting fibers of PANI:PAN composite could be use-ful for many applications that require a combination of electricalconductivity with isothermal stability.

Acknowledgements

Authors are thankful to the Ministry of Environment and Forestsof India (Project Grant No. 19-36/2007-RE) and Department ofApplied Chemistry for providing financial support and researchfacilities.

References

[1] M. Khalid, F. Mohammad, Synth. Met. 159 (2009) 119–122.[2] M.K. Ram, O. Yavuz, V. Lahsangah, M. Aldissi, Sens. Actuators B 106 (2005)

750–757.[3] A. Mirmohseni, A. Oladegaragoze, J. Appl. Polym. Sci. 85 (2002) 2772–2780.[4] A. Mirmohseni, W.E. Price, J. Membr. Sci. 100 (1995) 239–248.[5] A. Mirmohseni, A. Oladegaragoze, Synth. Met. 114 (2000) 105–108.[6] J.E.P. Silva, S.I.C. Torresi, R.M. Torresi, Corros. Sci. 47 (2005) 811–822.[7] Z.M. Tahir, E.C. Alocilja, D.L. Grooms, Biosens. Bioelectron 20 (2005) 1690–1695.[8] P. Camurlu, A. Cirpan, L. Toppare, Mater. Chem. Phys. 92 (4) (2005) 13–418.[9] J. Wang, C.O. Too, D. Zhou, G.G. Wallace, J. Power Sources 140 (2005) 162–167.10] A. Mirmohseni, R. Solhjo, Eur. Polym. J. 39 (2003) 219–223.11] H. Qiu, H. Li, K. Fang, J. Li, W. Mao, S. Luo, Synth. Met. 148 (2005) 71–74.12] O.P. Dimitriev, Macromolecules 37 (2004) 3388–3395.13] S.A. Chen, L.C. Lin, Macromolecules 28 (1995) 1239–1245.14] S. Koul, R. Chandra, S.K. Dhawan, Sens. Actuators B 75 (2001) 151–159.15] A.A. Ahmed, F. Mohammad, J. Solid State Phenom. 111 (2006) 99–102.16] A.A. Ahmed, F. Mohammad, J. Solid State Phenom. 111 (2006) 95–98.17] J.F. Douglas, E.J. Garboczi, Adv. Chem. Phys. 91 (1995) 85–153.18] R. Zallen, The Physics of Amorphous Solids, Wiley-VCH Verleg Gmbh & Co.

KGaA, Weinheim, New York, 1983, pp 135–204.19] D.S. McLachlan, M. Blaszkiewicz, R.E. Newham, J. Am. Ceram. Soc. 73 (1990)

2187–2203.20] Instruction Manual, Scientific Equipments and Services, Roorkee, India, 2000.21] M. Khalid, F. Mohammad, Exp. Polym. Lett. 1 (2007) 711–716.22] M. Khalid, F. Mohammad, J. Appl. Polym. Sci., in press, doi:10.1002/app.29195.

23] J. Stejskal, I. Sapurina, J. Prokes, J. Zemek, Synth. Met. 105 (1999) 195–202.24] C.N.R. Rao, Chemical Application of Infrared Spectroscopy, Academic Press, New

York, 1963.25] G. Du, J. Avlyanov, C.Y. Wu, K.G. Reimer, A. Benatar, A.G. MacDiarmid, A.J.

Epstein, Synth. Met. 85 (1997) 1339–1340.26] A. Khatoon, M. Khalid, F. Mohammad, J. Appl. Polym. Sci. 108 (2008) 3769–3780.