Synthesis and characterization of water-soluble polyaniline films

Synthetic Metals 161 (2011) 806–811

Contents lists available at ScienceDirect

Synthetic Metals journal homepage: www.elsevier.com/locate/synmet

Synthesis and characterization of water-soluble polyaniline films Liang Shao a , Jianhui Qiu a,b,∗ , Mingzhu Liu a,∗∗ , Huixia Feng c , Lin Lei b , Guohong Zhang b , Yang Zhao b , Chunmei Gao a , Lijun Qin a a

College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, PR China Department of Machine Intelligence and Systems Engineering, Faculty of Systems Engineering, Akita Prefectural University, Akita 015-0055, Japan c College of Petrochemical Technology, Lanzhou University of Technology, Lanzhou 730050, PR China b

a r t i c l e

i n f o

Article history: Received 5 October 2010 Received in revised form 23 January 2011 Accepted 3 February 2011 Available online 16 March 2011 Keywords: Water-soluble polyaniline Double-strand Stack Photoluminescence

a b s t r a c t Water-soluble polyaniline (PANI) films were synthesized by using poly(2-acrylamido-2-methyl propanesulphonic acid) (PAMPS) as a water-soluble dopant. The aqueous solution conductivities of PANI/PAMPS films were in the range of 10−1 to 100 mS/cm which were increased compared with PAMPS films aqueous solution. The structure and microstructure characteristics of PANI/PAMPS films which varied greatly with different molar ratios of aniline/AMPS were investigated by SEM, UV–vis absorption spectroscopy and XRD analysis. Moreover, the photoluminescence properties of PANI/PAMPS films were studied, and water-soluble PANI having appropriate size fitted to the increase of fluorescence emission intensity. PANI/PAMPS films were also investigated by FTIR spectroscopy and TG analysis. © 2011 Elsevier B.V. All rights reserved.

1. Introduction The discovery of conducting polymers and their doping over the full range from insulator to metal by Heeger, MacDiarmid, Shirakawa and co-workers has been landmark research leading to what has been designated as the “fourth generation of polymer materials”. Polyaniline (PANI) is a family of polymers that represents the oldest electroactive synthetic material [1,2]. As a conductive material, PANI is unique among the family of conducting polymers since its doping level can be readily controlled through an acid doping/base dedoping process [3–5]. However, conducting PANI is not generally processable due to its less solubility for almost of all solvents and its poor melt property. In addition, the potential for application of PANI is still limited by its intractability resulting from the stiffness of backbone and H-bonding interactions between adjacent chains [6,7]. Many research efforts have been devoted to enhance the solubility of polyaniline in common solvents. These efforts, coupled with the ability to quantitatively distinguish the various intrinsic redox states, have substantially enhanced the potential of the aniline polymers in practical applications, such as in corrosion protection of metals, light-emitting devices, and as materials for catalysts, electrodes and sensors [8,9].

Recently, environmental concerns have placed restrictions on the commercial use of many organic solvents. These concerns in turn have encouraged the use of polymers that can be processed in aqueous media. Thus, water solubility of polymers has become an important factor to be taken into account when commercial applications are considered. Therefore, preparation of water-soluble PANI is required, especially when PANI is used as a component of aqueous coatings. Two methods were reported to prepare water soluble or dispersible PANI. One was grafting a sulfonic or phosphoric acid group onto the benzene ring or nitrogen atom [10,11]. The other was synthesizing PANI by using functional acids as dopants such as polymeric sulfonic acids [12,13] and polymeric phosphoric acid [14]. Obviously, these methods were time-consuming and expensive. Few reports were found in the literature to employ water-soluble dopants. In this paper, we described the chemical synthesis of watersoluble PANI blend films by using poly(2-acrylamido-2-methyl propanesulphonic acid) (PAMPS) as a water-soluble dopant. Because of the hydrophilic nature of the PAMPS, the PANI/PAMPS blend films were soluble in water. Their morphological structure and properties in the form of films were examined with the increase of the content of PANI in the films. 2. Experimental

∗ Corresponding author at: College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, PR China. Tel.: +81 184 27 2134; fax: +81 184 27 2188. ∗∗ Corresponding author. Tel.: +86 931 8912387; fax: +86 931 8912582. E-mail addresses: [email protected] (J. Qiu), [email protected] (M. Liu). 0379-6779/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2011.02.003

2.1. Materials Aniline (An) monomer (purity 99.5%, Tianjin Baishi Chemical Industry Co., Ltd., Tianjin, China) was vacuum distilled prior

L. Shao et al. / Synthetic Metals 161 (2011) 806–811

807

AMPS: H2C CH O C NH H3C C CH3 H2C SO3H

SO3

SO3

S-3 polymerization SO3H

Anmol:AMPSmol = 0.1:1 SO3H

SO3H

(b) PANI-PAMPS polymeric complex

SO3H

S-4 (S-5) SO3H

HO3S SO3H

Anmol:AMPSmol = 0.2:1 (0.3:1)

SO3H

(c) Stacks of double-strand PANI-PAMPS chains were well-dispersed

(a) PAMPS linear polymer (S-1)

S-6 Anmol:AMPSmol = 0.4:1 (d) Stacks of double-strand PANI-PAMPS chains were aggregated

= PANI chain

= PAMPS chain

= Stacks of double-strand PANI-PAMPS chains SO3

SO3

=

SO3 N H

NH

SO3 N H

SO3 SO3

N H

N H

NH

Double-strand PANI-PAMPS chains Fig. 1. Preparation routes and structural investigation of PANI/PAMPS films.

to its use. Other chemicals were used without further purification. These were: 2-acrylamido-2-methyl propanesulphonic acid (AMPS) (Shandong Linyi Viscochem Co., China), ammonium persulfate (APS; purity 98.0%, Tianjin Baishi Chemical Industry Co., Ltd., Tianjin, China).

2.2. Preparation of PANI/PAMPS films Our approach to prepare PANI/PAMPS films consisted of two major steps as shown in Fig. 1. In the first step, viscous AMPS-based polymeric dopant (PAMPS) was obtained by aqueous solution polymerization of AMPS (27.5 mmol) using APS as an initiator at 60 ◦ C under a nitrogen atmosphere for 5 h. In the second step, distilled aniline (between 1.1 mmol and 11 mmol) was added to the PAMPS aqueous solution which was prepared in the first step, and stirring with glass rod to make aniline dispersed in PAMPS aqueous solution at 0–5 ◦ C. After that, 5 mL of APS solution (molar ratio: aniline/APS = 1.5/1) was added dropwise to the solution within 10 min so as to start the polymerization. The mixture was allowed to polymerize under a nitrogen atmosphere for another 24 h at 0–5 ◦ C. The films were prepared by pouring the solutions on a teflon board and drying at room temperature as shown in Fig. 2. The samples were dried at 80 ◦ C for 48 h prior to measurements.

2.3. Characterization techniques Conductivity measurements of PAMPS and PANI/PAMPS mixtures aqueous solution (0.1 g/100 mL) were carried out at room temperature using DDSJ-308A conductivity meter, DJS-1 C conductivity electrode and T-818-B-6 temperature electrode (Shanghai Precision and Scientific Instrument Co., Ltd., Shanghai, China). Conductivity measurements of PAMPS and PANI/PAMPS films were carried out at room temperature using four-probe device with measure range 10−4 to 105  cm (KDY-1 Resistivity Measur-

Fig. 2. PANI/PAMPS films.

808

L. Shao et al. / Synthetic Metals 161 (2011) 806–811

Fig. 3. SEM images of PAMPS and PANI/PAMPS films: (a) S-1; (b) S-2; (c) S-3; (d) S-4; (e) S-5; (f) S-6.

ing Instrument, Kunde Technology Co., Ltd., Guangzhou, China) and high resistivily meter with measure range 104 to 1013  cm (MCP-HT450 Hiresta-up, Mitsubishi Chemical Analytech Co., Ltd., Japan).Electronic absorption spectra of PANI/PAMPS films were recorded in aqueous solution (0.1 g/100 mL) in the wavelength range of 290–1000 nm at room temperature using the Lamda 35 UV–visible spectrophotometer (PerkinElmer, USA). Fluorescent excitation and fluorescence spectra were obtained from a LS 55 Luminescence Spectrometer (PerkinElmer) for the aqueous solution samples of PANI/PAMPS films (0.1 g/1 L). The FTIR measurements (Impact 400, Nicolet, Waltham, MA) were carried out using the KBr pellet method. The TA Instrument 2050 thermogravimetric analyzer was used for TGA; heating rate was 10 ◦ C/min from 45 to 550 ◦ C in the air. The X-ray diffraction (XRD) patterns were recorded in the range of 2 = 5–50◦ by step scanning with the XRD-6000 (Shimadzu, Japan); Nickel-filter Cu K␣ radiation ( = 0.15418 nm) was used with a generator voltage of 40 kV and a current of 30 mA. A field emission scanning electron microscope (FE-SEM, Hitachi High-Technologies CO. S-4300 model) was used to get SEM images.

3. Results and discussion 3.1. Microstructure characteristics As shown in Fig. 3, the SEM of PANI/PAMPS films which synthesized under the different amount of aniline varied greatly. Fig. 3(a) depicted typical SEM image of PAMPS linear polymer which could be seen in Fig. 1(a), and the SEM image of S-2 as shown in Fig. 3(b) was similar to S-1 because of less PANI.As shown in Fig. 1(b), aniline monomers were absorbed onto a polyanion chain dissolved in solution as a resulting adduct; and then, the attached aniline monomers were oxidatively polymerized to form the PAMPS-templated polymer of aniline namely PANI–PAMPS polymeric complex [15–19]. The SEM images of this PANI–PAMPS polymeric complex could be shown in Fig. 3(c). With the amount of the aniline increasing (S-4 and S-5), the double-strand polymers were synthesized as shown in Fig. 1(c), and the stacks of double-strand PANI–PAMPS chains were well-dispersed on the surface of PAMPS linear matrix [18–22]. Moreover, this scheme accorded with the SEM images as shown in Fig. 3(d) and (e). Compared with S-4 and S-5, the stacks

L. Shao et al. / Synthetic Metals 161 (2011) 806–811

809

Fig. 4. Aqueous solution of PAMPS and PANI/PAMPS mixtures (0.1 g/100 mL): (a) S-1; (b) S-2; (c) S-3; (d) S-4; (e) S-5; (f) S-6.

of double-strand PANI–PAMPS chains were not well dispersed and they aggregated significantly in the surface of PAMPS linear matrix as shown in Figs. 1(d) and 3(f) [23,24]. 3.2. UV–vis absorption spectra

3.3. XRD analysis To investigate the solid-state properties of PANI/PAMPS films, they were finely powdered and subjected to XRD analysis as shown in Fig. 6. In general, a polymer chain has both amorphous and crystalline domains in the matrix, and the percentage of the respective domains varies depending upon their backbone. A PANI backbone is highly rigid because of its linear structure and less flexible to chain folding to induce a crystalline domain. Therefore, undoped PANI chains (emeraldine base) are normally observed as highly amorphous polymers. In the presence of sulfonic acids, the dopant-

Intensity (a.u.)

Aqueous solution of PAMPS and PANI/PAMPS films (0.1 g/100 mL) was shown in Fig. 4. Interestingly, these aqueous solutions were very stable for more than 2 months under normal ambient conditions. The UV/vis absorption spectra of aqueous solution of PAMPS and PANI/PAMPS films were presented in Fig. 5. These spectra depicted the feature characteristic of protonated PANI referred to above, implying that the polymers in the aqueous solutions and films were PANI in protonated form. This confirmed the effective solubilization of PANI doping by PAMPS in an aqueous environment. A typical UV/vis absorption spectrum of protonated PANI, polyemeraldine green form, had three distinct absorption bands around 350, 430 and 790 nm. The absorption band around 350 nm was arised from ␲ → ␲* electron transition within benzenoid segment. The absorption band around 430 nm was related to the protonation of the PANI backbone, while the absorption band around 790 nm was assigned as the polaron band: the conducting emeraldine salt state of the PANI appears around 790 nm [25,14,26]. Since the peaks around 430 nm and 790 nm were observed in all aqueous solution of PANI/PAMPS films, as the similar cases to the spectra in Fig. 5, the present all PANI/PAMPS films were suggested to have conjugated PANI emeraldine salt structure even in the polymerization system in the presence of PAMPS [27,28]. Generally, as the molar ratio of An:AMPS increased from 0.04 to 0.4, the intensity of absorption around 790 nm was enhanced in the earlier phase and weakened later, accompanied with the incremental absorption

around 430 nm. Earlier studies had shown that the intensity of the polaron band decreases with a decrease in molecular weight and level of protonation [29,30]. The intensity of the polaron band of S-4 and S-5 was higher than other samples, and we proposed that there were two possible reasons. On one hand, the stacks of double-strand polymers might take the shape of a tight coil chain. The shape of the stacking controlled the morphology of the polymerized product. Tight-coiled stacks of double-strand polymer resulted in globular PANI–PAMPS polymeric complex which could be shown in Fig. 3(d) and (e). Moreover, these tight-coiled stacks of double-strand polymer could enhance the intensity of the polaron band [12,19,25]. On the other hand, compared with S-4 and S-5, the stacks of double-strand PANI–PAMPS chains of S-6 were not well dispersed and they aggregated significantly in the surface of PAMPS linear matrix as shown in Fig. 3(d). The aggregating of these stacking might result in a decrease in molecular weight and protonation level of PANI. Therefore, S-6 exhibited a weak intensity of the polaron band [18,19,31].

a b c d e f g 10

20

30

2θ Fig. 5. UV–vis absorption spectrum of aqueous solution of PAMPS and PANI/PAMPS films (0.1 g/100 mL): (a) S-1; (b) S-2; (c) S-3; (d) S-4; (e) S-5; (f) S-6.

o

40

50

Fig. 6. XRD patterns: (a) S-1; (b) S-2; (c) S-3; (d) S-4; (e) S-5; (f) S-6; (g) undoped PANI (emeraldine base).

810

L. Shao et al. / Synthetic Metals 161 (2011) 806–811

1000

600 400

0.4

f c

400

b a

200 0 460

480

500

Wavelength (nm)

520

c

540

4000

3000

2000

620

0.3

862

0.2

1035

0.1

1453 1396 1306

0.0

An:AMPS (Molar ratio)

1650

d

600

b

1564

200

2991 2930

e

800

a

800

% Transmittance

FI (A.U.)

Fluorescence Intensity (A.U.)

1000

1000

Wavenumbers (cm-1)

Fig. 7. Fluorescence emission spectra (ex = 244) of aqueous solution of PAMPS and PANI/PAMPS films (0.1 g/1 L): (a) S-1; (b) S-2; (c) S-3; (d) S-4; (e) S-5; (f) S-6.

Fig. 8. FTIR spectra analysis: (a) S-1; (b) S-4; (c) S-5.

3.4. Fluorescence spectra The fluorescence emission spectra of aqueous solution of PAMPS and PANI/PAMPS films (0.1 g/1 L) with an excitation wavelength of 244 nm were given in Fig. 7. The fluorescence emission intensity of the samples was enhanced in the earlier stage and weakened later with increasing PANI concentration. The reason for the high emission intensity might result from the ␲-electrons extensive delocalization formed a large conjugated system in the polymer backbone structure [37–39]. Interestingly, PANI rings as a fluoroionophore having appropriate size fit to the increase of fluorescence emission intensity generated by the tight coil PANI chains [40]. Anilkumar and Jayakannan [22,41] have shown that the protonation level was very crucial in obtaining highly luminescent PANI materials. Therefore, the decreasing in protonation level might result in the weakening of fluorescence emission intensity, and this was consistent with the analysis of UV–vis absorption spectrum. Furthermore, less ordering of S-5 which was proved in XRD analysis could be also seen as one possible reason for the weakening of fluorescence emission intensity [42,43]. The photoluminescent properties of these water soluble PANI/PAMPS films may possess great potential for numerous optical and electronic applications [37]. 3.5. FTIR spectra Fig. 8 depicted the FTIR spectra of PAMPS and PANI/PAMPS films. The peaks at 1650, 2991 and 2930 cm−1 were attributed to C O, CH3 and CH2 which were present in PAMPS [44,45]. As shown in Fig. 8(b) and (c), the main peaks consistent with quinone and

benzene ring could be observed at 1564 and 1453 cm−1 which confirmed the presence of PANI [18,46]. Furthermore, the PANI/PAMPS was also subjected to FTIR analysis to understand the doping behaviors. The new peaks were present in the doped samples (S-4 and S-5) at 1035 and 862 cm−1 for the NH+ . . .SO3 − interactions between the PANI chains and dopant PAMPS, and the S–O (unsym) stretching vibration. Besides, the peaks at 1306 and 620 cm−1 were attributed to O S O (sym) and C–S stretching vibrations, respectively [32,33]. 3.6. Thermal stability The TGA curves of PAMPS and PANI/PAMPS samples were shown in Fig. 9. S-1 curve exhibited two-stage degradation behaviors. The first stage of decomposition of PAMPS started at about 190 ◦ C. With the temperature increasing to 350 ◦ C, the second decomposition took place, which was accordant with the literatures [45,47]. As shown in Fig. 9(b)–(d), PANI chains started to decompose around 280 ◦ C [15,48]. The onset decomposition temperature of PANI was enhanced as the molar ratio of An/AMPS increased. Moreover, this behavior confirmed the increased thermal stability of PANI. This could be explained by the advantage of double-strand PANI–PAMPS chains as follows: the anionic dopants, incorporated as parts of the molecular complex, were strongly attached to the PANI chains, and the thermal stability of the polymer was improved

100 80

e d

Weight (%)

polymer undergoes various interactions, which tend to organize the polymer chains in 3D highly ordered fashions. The highly organized and ordered structures reflect on the low angle region of the XRD plot [32,33]. We noted the peak on the low angle region (2 = 7.6◦ ) in Fig. 6(a)–(e), and the peak at 2 = 7.6◦ was only observed for highly ordered samples in which the PANI interplanar distance increased by the effective penetrating of dopant molecules [33–35]. Moreover, undoped PANI chains (emeraldine base) were normally observed as highly amorphous polymers, and there was no peak at 2 = 7.6◦ in Fig. 6(g). Additionally, in Fig. 6(f), the peak at 2 = 7.6◦ was absent, indicating less ordering of S-6 because the stacks of double-strand PANI–PAMPS chains were aggregated significantly in the surface of PAMPS linear matrix, which was further evident from its SEM image [18,33,36].

60

c 40

b a

20 0

100

200

300

400

500

Temperature (oC) Fig. 9. TGA curves of PAMPS and PANI/PAMPS films: (a) S-1; (b) S-3; (c) S-4; (d) S-5; (e) S-6.

L. Shao et al. / Synthetic Metals 161 (2011) 806–811

811

Table 1 Polymerization conditions and conductivity characteristics. Samples

An:AMPS (molar ratio)

Film conductivity (mS/cm)

Aqueous solution conductivity (mS/cm)

Distilled water S-1 S-2 S-3 S-4 S-5 S-6

– 0:1 0.04:1 0.1:1 0.2:1 0.3:1 0.4:1

– 3.226 × 10−4 8.403 × 10−4 2.899 × 10−3 2.525 × 10−2 3.165 × 10−1 6.623 × 10−1

0.009 0.776 0.930 0.960 1.149 1.248 1.305

[18,19]. However, degradation rate of PANI (S-6) was increased compared with S-5 as shown in Fig. 9(e) and (d). It could mainly attributed to the decreasing molecular weight and protonation level of S-6 which was explained above [49,50]. 3.7. Conductivity characteristics The conductivities of PAMPS and PANI/PAMPS films and aqueous solution (0.1 g/100 mL) were shown in Table 1. The aqueous solution conductivity of PAMPS was greater than distilled water, and PAMPS film also had a conductivity of 3.226 × 10−4 mS/cm, this was most probably because PAMPS was found to be a protonconducting polymer [51]. Moreover, the conductivities of PANI/PAMPS films and their aqueous solutions were enhanced compared with PAMPS’, and the conductivities were enhanced with the increase of aniline contents. As for solid films, this was because PANI as a conductive component could improve the conductivity. In addition, for S-3, S-4 and S-5 films, the conductivities were obviously improved, the reason could be that the structures of PANI–PAMPS polymeric complex and well-dispersed of the stacks of double-strand PANI–PAMPS chains on the surface of PAMPS linear matrix as shown in Fig. 1(b) and (c) and Fig. 3(c)–(e) were in favor of the increase of films’ conductivity. However, the conductivity of S-6 film was added less which probably because the stacks of double-strand PANI–PAMPS chains were not well dispersed and they aggregated significantly in the surface of PAMPS linear matrix as shown in Figs. 1(d) and 3(f). In addition, similar phenomenon was shown as for aqueous solution conductivities, and this was because water-soluble PANI as a conductive component could also improve the solution conductivity. As a result, it could be concluded that the water-soluble PANI emeraldine salt was synthesized and doped with PAMPS. 4. Conclusions In summary, water-soluble PANI films were synthesized by using PAMPS as a water-soluble dopant. The structure and microstructure of PANI/PAMPS films varied greatly with different molar ratios of An/AMPS, and the well-dispersed stacks of double-strand PANI–PAMPS chains had great significance to the characteristics of the PANI/PAMPS films. Moreover, PANI rings as a fluoroionophore having appropriate size fit to the increase of fluorescence emission intensity. The photoluminescent properties of these water soluble PANI/PAMPS films may have great potential for numerous optical and electronic applications. Recently, owing to consideration of environmental protection, preparation of watersoluble PANI has drawn scientific attention. Thus, water solubility of PANI has become an important factor to be taken into account while commercial applications were considered, especially when it was used as a component of aqueous coatings.

[2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49]

References [50] [1] C.K. Chiang, C.R. Fincher, Y.W. Park, A.J. Heeger, H. Shirakawa, E.J. Louis, et al., Phys. Rev. Lett. 39 (1977) 1098–1101.

[51]

V.A. Adrian, A.S. Jose, E. Gustavo, J. Am. Chem. Soc. 127 (2005) 11318–11327. A.J. Heeger, J. Phys. Chem. B 105 (2001) 8475–8491. J. Zhang, L.B. Anna, M. Daniel, J. Am. Chem. Soc. 125 (2003) 9312–9313. W. Yen, W.F. Walter, E.W. Gary, R. Anjan, A.G. MacDiarmid, J. Phys. Chem. 93 (1989) 495–499. J.X. Huang, B.K. Richard, J. Am. Chem. Soc. 126 (2004) 851–855. J.E. Yoo, J.L. Cross, T.L. Bucholz, J. Mater. Chem. 7 (2007) 1268–1275. F. Chen, C. Nuckolls, S. Lindsay, Chem. Phys. 324 (2006) 236–243. S. Bhadra, D. Khastgir, N.K. Singha, J.H. Lee, Prog. Polym. Sci. 34 (2009) 783– 810. A.D. Bhavana, Y. Insun, S.F. Michael, J. Am. Chem. Soc. 126 (2004) 52–53. P. Anilkumar, M. Jayakannan, Langmuir 24 (2008) 9754–9762. H. Tetsuo, N. Takumi, K. Noriyuki, Synth. Met. 156 (2006) 1327–1332. J.M. Davey, C.O. Too, S.F. Ralph, L.A.P. Kane-Maguire, G.G.W.C. Partridge, Macromolecules 33 (2000) 7044–7050. Y.H. Geng, Z.C. Sun, J. Li, X.B. Jing, X.H. Wang, F.S. Wang, Polymer 40 (1999) 5723–5727. W. Jia, E. Segla, D. Kornemandel, Y. Lamhot, M. Narkis, A. Siegmann, Synth. Met. 128 (2002) 115–120. R. Sucharita, M.F. Jacqueline, N. Ramaswamy, T. Sukant, K. Jayant, A.S. Lynne, et al., Biomacromolecules 3 (2002) 937–941. E. Vitoratos, S. Sakkopoulos, E. Dalas, P. Malkaj, C. Anestis, Curr. Appl. Phys. 7 (2007) 578–581. L. Shao, J.H. Qiu, H.X. Feng, M.Z. Liu, G.H. Zhang, J.B. An, et al., Synth. Met. 159 (2009) 1761–1766. L.f. Sun, H. Liu, C. Robert, S.C. Yang, Synth. Met. 84 (1997) 67–68. K.C. Chang, G.W. Jang, C.W. Peng, C.Y. Lin, J.C. Shieh, J.M. Yeh, et al., Electrochim. Acta 52 (2007) 5191–5200. P. Anilkumar, M. Jayakannan, Macromolecules 41 (2008) 7706–7715. P Anilkumar, M. Jayakannan, J. Phys. Chem. B 113 (2009) 11614–11624. L. Shao, J. Qiu, M. Liu, H. Feng, G. Zhang, L. Qin, Synth. Met. 160 (2010) 143–149. C. Yang, P. Liu, Synth. Met. 160 (2010) 345–350. R. Madathi, P. Surendra, R.R. Chelanattu, Macromol. Rapid. Commun. 19 (1998) 119–122. J. Laska, J. Widlarz, Synth. Met. 135–136 (2003) 261–262. G.L. Yuan, N. Kuramoto, S.J. Su, Synth. Met. 129 (2002) 173–178. Z. Niu, J. Liu, L.A. Lee, M.A. Bruckman, D. Zhao, G. Koley, et al., Nano Lett. 7 (2007) 3729–3733. Y. Cao, P. Smith, A.J. Heeger, Synth. Met. 32 (1989) 263–281. K.G. Neoh, T.T. Young, N.T. Looi, E.T. Kang, K.L. Tan, Chem. Mater. 9 (1997) 2906–2912. Z. Peng, L. Guo, Z. Zhang, B. Tesche, T. Wilke, D. Ogermann, et al., Langmuir 22 (2006) 10915–10918. M. Jayakannan, S. Annu, S. Ramalekshmi, J. Polym. Sci. Part B: Polym. Phys. 43 (2005) 1321–1331. P. Anilkumar, M. Jayakannan, Langmuir 22 (2006) 5952–5957. D. Bruno, R. Patrice, F. Pavol, D. David, P.T. Jean, P. Adam, Chem. Mater. 13 (2001) 4032–4040. M.J. Antony, M. Jayakannan, J. Phys. Chem. B 111 (2007) 12772–12780. A. Benyoucef, F. Huerta, M.I. Ferrahi, E. Morallon, J. Electroanal. Chem. 624 (2008) 245–250. Z. Huseyin, E. Belgin, Polym. Adv. Technol. 21 (2010) 216–223. J.S. Benco, H.A. Nienaber, W.G. McGimpsey, J. Photochem. Photobiol. A 162 (2004) 289–296. S. Xiong, Q. Wang, Y. Chen, Mater. Chem. Phys. 103 (2007) 450–455. P.S. Partha, K. Pradip, A. Basudam, React. Funct. Polym. 68 (2008) 1103–1112. P. Anilkumar, M. Jayakannan, J. Phys. Chem. C 111 (2007) 3591–3600. X. Hu, K. Tang, S.G. Liu, Y.Y. Zhang, G.L. Zou, React. Funct. Polym. 65 (2005) 239–248. J. Gong, J. Yu, Y. Chen, L. Qu, Mater. Lett. 57 (2002) 765–770. L. Hechavarríam, H. Hu, M.E. Rincón, Thin Solid Films 441 (2003) 56–62. Y. Shen, J. Xi, X. Qiu, W. Zhu, Electrochim. Acta 52 (2007) 6956–6961. M. Trchova, I. Sedenkova, E. Tobolkova, J. Stejskal, Polym. Degrad. Stabil. 86 (2004) 179–185. Y.A. Aggour, Polym. Degrad. Stabil. 45 (1994) 273–276. A. Gök, M. Omastová, J. Prokeˇs, Eur. Polym. J. 43 (2007) 2471–2480. I. Yu, B.A. Deore, C.L. Recksiedler, T.C. Corkery, A.S. Abd-El-Aziz, M.S. Freund, Macromolecules 38 (2005) 10022–10026. C.R. Paula, M. Marilda, M.G. Carlos, P.S. Gabriel, A. Miguel, H.S. Wido, et al., Eur. Polym. J. 37 (2001) 2217–2223. J. Qiao, H. Takeo, O. Tatsuhiro, Polymer 46 (2005) 10809–10816.