Conductivity and dielectric properties of polyvinyl alcohol–polyvinylpyrrolidone poly blend film using non-aqueous medium

Journal of Non-Crystalline Solids 357 (2011) 3751–3756

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Journal of Non-Crystalline Solids j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j n o n c r y s o l

Conductivity and dielectric properties of polyvinyl alcohol–polyvinylpyrrolidone poly blend film using non-aqueous medium N. Rajeswari a, S. Selvasekarapandian a,⁎, S. Karthikeyan b, M. Prabu a, G. Hirankumar a, H. Nithya c, C. Sanjeeviraja d a

Department of Physics, Kalasalingam University, Krishnankoil-626 190, Tamilnadu, India School of Advanced Sciences, VIT University, Vellore Tamilnadu, India Physics division, Bu-DRDO, Bharathiar university, Coimbatore- 641046, Tamilnadu, India d Department of physics, Alagappa university, Karaikudi, Tamilnadu, India b c

a r t i c l e

i n f o

Article history: Received 29 March 2011 Received in revised form 25 July 2011 Available online 30 August 2011 Keywords: Poly blend; PVA; PVP; FTIR; Impedance analysis

a b s t r a c t Several methods such as copolymerization, plasticization and blending etc., have been used to modulate the conductivity of polymer electrolytes. Polymer blending is one of the most important contemporary ways for the development of new polymeric materials and it is a useful technique for designing materials with a wide variety of properties. Polymer blend electrolyte has been prepared with different concentrations of PVA and PVP by solution casting technique using DMSO as solvent. The prepared films have been investigated by different techniques. The increase in amorphous nature of the polymer electrolytes has been confirmed by XRD analysis. The FTIR analysis reveals that the interchain hydrogen bonding within a PVA–PVP blends. The dielectric permittivity (ε*) and modulus (M*) have been calculated from the ac impedance spectroscopy in the frequency range 42 Hz–1 MHz and the temperature range 308–373 K. The maximum conductivity has been found to be 1.58 × 10 − 6 S cm − 1 at room temperature for 70PVA:30PVP concentration. The conductivity has been increased to 5.49 × 10− 5 S cm − 1 when the temperature is increased to 373 K. The activation energy of all samples was calculated using the Arrhenius plot and it has been found to be 0.53 eV to 0.78 eV. © 2011 Elsevier B.V. All rights reserved.

1. Introduction The dielectric properties of polymer materials play an important role in device applications such as high performance capacitors, electrical cable insulation and electronic packing [1]. Among the various approaches that have been adopted to enhance the conductivity and dimensional stability of polymer electrolytes, the following three are important (i) The use of low-volatility liquids with high dielectric constants as plasticizers in the polymer host [2–4]. (ii) The incorporation of inert fillers into polymer film [5]. (iii) Blending the polymer with another polymer that has a high fluidity [6,7]. Polymer electrolyte prepared by above techniques has not only high ionic conductivity but also favorable mechanical strength. Polymer blends have become commercially and technologically more important than the fabrication of homopolymers and copolymers in the last decade because blending allows one to create a new material with specific properties for the desired application at low cost. These properties mainly depend on the characteristics of the parent homo polymers and the blend composition [8]. The study of these systems is receiving increasing attention since an adequate mixture of the polymers can be

⁎ Corresponding author. Tel.: + 91 9443703089. E-mail address: [email protected] (S. Selvasekarapandian). 0022-3093/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2011.07.037

used to optimize the performance of polymer based systems in a cheaper and quicker way compared with synthesizing new polymer. Many blend electrolytes have been reported based on PEO–PAN [9], P(VdF-HFP)–PVAc [10], PVC–PMMA [11], PVAc–PMMA [12], PVdF– PEMA [13] and so on. PVA and PVP has been a favorable choice as polymer electrolyte. PVA and PVP blend suggests good mutual compatibility, higher stability and amorphous in nature. PVA is a semicrystalline polymer studied extensively because of its many interesting physical properties which arise from the presence of OH groups and the hydrogen bond formation. PVA is used in many biomedical and pharmaceutical applications due to its advantages such as nontoxic, noncarcinogenic and bioadhesive characteristics with the ease of processing. PVA is a potential material having a very high dielectric strength (N1000 kV/mm) [1]. PVP is a vinyl polymer possessing planar and highly polar side groups due to the peptide bond in the lactam ring. It is an amorphous polymer. The pyrrolidone rings in PVP contain a proton accepting carbonyl group. PVP deserves a special attention among the conjugated polymers because of its good environmental stability, easy processability and moderate electrical conductivity. Both of the PVA and PVP are soluble in DMSO and miscible in all proportions. When these two polymers are mixed, the interactions between PVA and PVP are expected to occur through interchain hydrogen bonding between carbonyl group of PVP and the hydroxyl

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group of PVA. The study of dielectric loss as a function of temperature and frequency has been used to characterize the molecular motion and dielectric relaxation behavior of the polymer. PVA–PVP is a potential material having good charge storage capacity and dopant dependent electrical and optical properties. Hefford et al. and R. Vijayalakshmi et al. reported the miscibility aspects for PVA–PVP blend [14,30]. S. N. Cassu et al. studied the secondary relaxations of the PVA–PVP blend [15]. Ch. V. Subba Reddy et al. reported the dielectric properties of PVA–PVP [1]. Literature survey reveals that the conductivity studies of PVA–PVP based polymer blend are scarce. Hence the aim of the present work is to study the conductivity and dielectric properties of PVA–PVP polyblend electrolyte prepared based on different compositions of PVA and PVP.

e Intensity (a.u)

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d c b a

2. Experimental technique 10

2.1. (PVA + PVP) polymer electrolyte film preparation PVA from MERCK (Mw-1, 25,000) and PVP (Mw-90,000) are used as the raw materials for the present polymer electrolyte. Film thickness of about 0.22–0.16 μm of the PVA–PVP polyblend have been prepared in different ratios [(50:50), (60:40), (70:30), (80:20) and (90:10) (PVA:PVP)] with DMSO as a solvent using a solution cast technique. The samples have been prepared by first dissolving PVA and PVP in DMSO and then stirred until homogeneous solution was obtained and the solution was poured into polypropylene dish and dried in oven at 70 °C for 6 days to ensure removal of the solvent traces. After drying the films have been peeled from Petri dishes. 2.2. Characterization of the polymer films X-ray diffraction patterns of the prepared samples have been recorded at room temperature on a Philips X'pert PRO diffractometer using CuKα radiation. FTIR spectra are recorded for the polymer electrolyte films in the range of 400–4000 cm − 1 at room temperature using a SHIMADZU-IR Affinity-1 spectrometer. Dielectric and conductivity measurements are made using HIOKI 3532 impedance analyzer in the range of 42 Hz–1 MHz and the temperature of 308 K– 373 K. The conductivity value depends on the bulk resistance; the impedance accuracy is ±0.97%. 3. Results 3.1. X-ray diffraction analysis XRD is a versatile, non-destructive technique that reveals detailed information about the crystallographic structure of materials and investigates the occurrence of complex formation between the polymers. The X-ray diffraction patterns of the PVA blend with PVP having different concentrations are shown in Fig. 1.

20

30

40

50

60

Fig. 3(a) shows the Nyquist plots for PVA blend with PVP polymer electrolyte samples of different compositions at room temperature. The figure consists of a high frequency depressed semicircle and low frequency spike. The equivalent circuit corresponding to the Nyquist plot of high conductivity sample 70PVA:30PVP has been given in Fig. 3(b). Fig. 4 shows the frequency dependent conductivity for 70PVA:30PVP polymer electrolytes as a function of different temperatures. The dc conductivity values for all the compositions of PVA:PVP polymer electrolytes at different temperatures have been tabulated in Table 2. The variation of room temperature conductivity and activation energy as a function of different PVA blends with PVP concentration is shown in Fig. 5. As the conductivity of the sample increases it can be noticed that Ea decreases. Fig. 6 shows the temperature dependence conductivity for all the prepared PVA blend with PVP concentration polymer electrolyte over the temperature range 308 K–373 K. The activation energy calculated for all the blended polymer films has been tabulated in Table 3. 3.4. Dielectric and modulus analysis Fig. 7 (a),(b) shows the frequency dependence of real ε′ (dielectric constant) and the imaginary ε″ (dielectric loss) for the film of high conductivity PVA with PVP at various temperatures. Fig. 8 (a, b) shows the Real (M′) and imaginary parts (M″) of the electric modulus as a function of

g f e %T

d c b a

3.3. AC conductivity analysis The ac impedance technique is a powerful method for characterizing the electrical properties of materials. In contrast to dc methods ac measurements can separate the individual contributions from the various bulk and interfacial polarization taking place in the electrolyte when stimulated by some external sinusoidal voltage.

80

Fig. 1. XRD pattern of (a) 50PVA:50PVP, (b) 60PVA:40PVP, (c) 70PVA:30PVP, (d) 80PVA:20PVP, (e) 90PVA:10PVP.

3.2. FTIR analysis FTIR spectroscopic technique has been proven to be a powerful tool in characterizing the detailed structure of polymer blend. The IR spectra of pure PVA, pure PVP and PVA–PVP blend with different concentrations recorded at room temperature in the region 400– 4000 cm − 1 are shown in Fig. 2.

70

2 (Degree)

4000

3500

3000

2500

2000

1500

1000

500

Wavenumber (cm-1) Fig. 2. FTIR pattern of (a) pure PVA, (b) pure PVP, (c) 50PVA:50PVP, (d) 60PVA:40PVP, (e) 70PVA:30PVP, (f) 80PVA:20PVP, (g) 90PVA:10PVP.

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50PVA:50PVP 60PVA:40PVP 70PVA:30PVP 80PVA:20PVP 90PVA:10PVP

40000

30000

20000

Activation Energy

0.75

Log

(Scm-1)

1.5x10-6

0.70

1.2x10-6

0.65

9.0x10-7

0.60

6.0x10-7

0.55

3.0x10-7

Log (Scm-1)

-Z'' (ohm)

1.8x10-6

0.80 50000

Activation energy

a

3753

10000

0 0

10000

20000

30000

40000

50000

0.50 50

Z' (ohm)

60

70

80

90

PVA & PVP Concentration

b

Fig. 5. Concentration dependent conductivity and activation energy.

Fig. 3. (a) The Nyquist plot for different concentrations of blend PVA–PVP at room temperature. (b): The equivalent circuit.

log ω (M′, M″ vs log ω) for 70PVA:30PVP at various temperatures. From Fig. 8 (a, b) the intensity decreased with raising temperature suggesting the presence of more than one type of relaxation mechanisms.

4. Discussion It is observed from Fig. 1, crystalline peaks at 2θ = 20.61° attributable to PVA, corresponding to (110) reflection. The above sharp peak is clearly observed in the diffractograms of the PVA–PVP blend sample with high PVA content. The shift in position of the peak in Fig. 1 [a, b, c] is due to hydrogen bonding interaction between PVA and PVP. Hydrogen bonding probably occurs between the OH groups in PVA and carbonyl group in PVP. The intensity of XRD pattern of PVA decreases as the amorphous nature of PVA increases with the addition of PVP. The highest amorphous sample is the blend of 70% PVA and 30% PVP. The peak at 2θ = 20.61° is small and broad. The increase in the amorphous nature causes a reduction in the energy barrier to the segmental motion of the polymer electrolyte resulting in high ionic conductivity [16,12].

FTIR spectroscopic technique has been proven to be a powerful tool in characterizing the detailed structure of polymer blend. It is very sensitive to the formation of hydrogen bonds [17]. The miscibility between the two polymers PVA–PVP blend is due to the hydrogen bonding between PVA hydroxyl groups and carbonyl groups of PVP monomeric units [18,19]. The IR spectra of pure PVA, pure PVP and PVA–PVP blend with different concentrations recorded at room temperature in the region 400–4000 cm− 1 are shown in Fig. 2. The absorption band, positions and its assignments for all prepared films are listed in Table 1. From Fig. 2 (a) for pure PVA, the bands at about 3480 cm− 1 are assigned to OH stretching [20]. The band corresponding to methylene group (CH2) asymmetric stretching vibration occurs at about 2910 cm− 1. The band at about 1078 cm− 1 corresponds to C\O stretching of acetyl groups present on the PVA backbone [21,22]. The vibrational bands at about 1694 cm − 1 correspond to C_C stretching of PVA and PVP [23]. The bands at 2179 cm− 1, 1731 cm− 1, 962 cm− 1 and 864 cm− 1 in Fig. 2 (b) have been assigned to C\N stretching, C_O stretching, C\C bonding and CH2 bending [24] vibrations of pure PVP respectively. The above mentioned peaks are present and the shifts in different concentrations of PVA and PVP are reported in Table 1. The peak around 2163 cm− 1 is attributed to the overtone ν(S_O) of DMSO casted PVA and PVP. The Nyquist plot (Fig. 3) consists of a high frequency depressed semicircle represented by a frequency dependent capacitor Cg parallel

-4.0

50PVA:50PVP 60PVA:40PVP

-4.0 70PVA:30PVP

70PVA:30PVP

-4.5

80PVA:20PVP 90PVA:10PVP

-4.4

(Scm )

-1

-4.8 -5.2

Log

Log

(Scm-1)

-5.0

-5.6 308K 323K 343K 363K 373K

-6.0 -6.4 1

2

3

4

5

6

Log F (Hz) Fig. 4. Conductance spectra for high conductivity polymer electrolyte.

-5.5

-6.0

-6.5

-7.0 2.6

2.7

2.8

2.9

3.0

3.1

3.2

3.3

1000/T (K) Fig. 6. Log σ vs 1000/T for different blends of PVA–PVP polymer electrolyte.

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N. Rajeswari et al. / Journal of Non-Crystalline Solids 357 (2011) 3751–3756

a

a

12000 70PVA:30PVP 10000

308K 323K 343K 363K 373K

6.0x1018

6000

M'

'

8000

70PVA:30PVP

8.0x1018

308K 323K 343K 363K 373K

4.0x1018

4000 2.0x1018

2000 0 1

2

3

4

5

0.0

6

1

Log (HZ)

b

5000 308K 323K 343K 363K 373K

3000

''

M ''

8.0x1017

0

4.0x1017 4

5

Log

(HZ)

5

6

1.2x1018

1000

3

(HZ)

308K 323K 343K 363K 373K

2.0x1018

2000

2

4

Log

70PVA:30PVP

2.4x1018

1.6x1018

1

3

b

70PVA:30PVP

4000

2

6

Log (HZ) Fig. 7. (a) Real dielectric constant of polymer electrolyte having high conductivity with frequency (b) imaginary dielectric constant of polymer electrolyte having high conductivity with frequency.

to a bulk resistor (Rb) and a low frequency spike represented by a constant phase element CPE. In this case the migration of ions may occur through the free volume of matrix polymer which can be represented by a resistor. The immobile polymer chains become polarized in the alternating field which can be represented by a capacitor. The ionic migration and bulk polarization are physically in parallel and therefore the semicircle at high frequency can be observed. The inclined straight line at the low frequency region could be the effect of electrode and electrolyte interface. The EQ software program developed by B.A. Boukamp et al. [26] has been used to extract the bulk electrical resistance (Rb) of the polymer electrolytes from the impedance plot of the low frequency side intercept on the Z′ axis. The highest room temperature conductivity value is found to be 1.58 × 10 − 6 S cm − 1 for the system 70PVA:30PVP. The ionic conductivity is calculated using the relation, σ = L=Rb A where L is the thickness of the film Rb is the bulk resistance A-contact area of the electrolyte film. Several researchers have provided different explanations for the conduction process in the polymer electrolyte system. Sunandana et al.

0.0 1

2

3

4

5

6

Fig. 8. (a) Real part of M′ with log frequency for high conductivity polymer electrolyte (b) imaginary part of M″ with log frequency for high conductivity polymer electrolyte.

reported that the conductivity depends on the mobile ion concentration, the vibrational frequency of the mobile ions at equilibrium and the entropy of activation [25]. The equivalent circuit corresponding to the Nyquist plot of high conductivity sample 70PVA:30PVP is given in Fig. 3 (b). The equivalent circuit is made of parallel combination of resistors (9009 Ω with error % of 2.012) and capacitors (1.325 × 10 − 10 F with error % of 51.819). A constant phase element CPEdl (1.523 × 10 − 7 F with error % of 2.4564) is used in the place of the pure capacitance Cdl, due to the observation of a depressed semicircle instead of a perfect semicircle caused by the inhomogeneous surface. The straight line that is inclined at an angle of 45° at the end of the semicircle corresponds to the finite length Warburg resistance (Ws) (4915 Ω with error % of 13.967) which is related to the solid state diffusion. The three regions have been observed from the conductance spectra (Fig. 4). The low frequency dispersion region observed can be ascribed to the space charge polarization at the blocking electrodes [27]. The intermediate region corresponds to the frequency independent plateau region and the extrapolation of the plateau to zero frequency gives the value of dc ionic conductivity at different temperatures. The high frequency dispersion region disappears at high temperature, since the jump frequency of the charge carriers increases with temperature [28]. The dc conductivity values for all the compositions of PVA:PVP polymer electrolytes at different temperatures have been presented in Table 2. Fig. 5 shows that when the conductivity of sample increases it can be noticed that activation energy decreases indicating that the ions in

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Table 1 The absorption band, position and is assignment of different concentration of PVA and PVP. Pure PVA

Pure PVP

Pure blend (PVA:PVP)

Wavenumber (cm− 1)

Assignments

Wavenumb er (cm− 1)

Assignments

Wavenumber (cm− 1)

3480 2888 2910

O\H stretching CH2 CH2 asymmetric stretching

1694 1760 1567 1470 1396 1278 1137 1078 943 856

C_C stretching C_O stretching O\H and C\H bending O\H and CH2 bending CH2 out of plane bending CH2 bending CH wagging C_O stretch CO symmetric stretching CH2 rocking

3506 2179 1731 962 864

O\H stretching C\N Stretching C_O stretching C\H out of plan rings bending CH2 bending

3401–3480 1607–1694

O\H stretching C_C stretching

2910–2996

CH2 asymmetric stretching

1708–1760 1607-1694 1590-1597

highly conducting samples require lower energy for migration. The high conductivity with low activation energy is observed for 70PVA:30PVP concentration. The activation energy is found to be low of the order of 0.53 eV for the high conductivity sample. Fig. 6 shows that the conductivity increases linearly with increases of temperature for all composition of PVA and PVP. The high conductivity exhibits in the composition of 70PVA:30PVP concentration. The regression values of the plots using linear fit have been found to be close to unity suggesting that the temperature dependent ionic conductivity for all the complexes obeys Arrhenius relation. σ = σ o expð−Ea =KTÞ where σo is related to the number of charge carriers in the films and Ea is related to the activation energy of ion transport associated with configurational entropy of the polymer chains and K is the Boltzmann constant. Based on the least squares analysis of the corresponding data, a good straight line fit has been obtained for all the PVA with PVP concentration. The experimental data indicates that the ionic conductivity has been enhanced with increase of temperature. The activation energy Ea is calculated for all the blended polymer film by linear fit of the Arrhenius plot. The calculated activation energy values have been listed in Table 3. From Table 3 the activation energy is low (0.53 eV) for the 70PVA:30PVP concentration. This is due to the amorphous nature of the polymer electrolytes that facilitate the ionic motion in the polymer network. The increase of activation energy with the increase of PVA concentration may be due to the increase in the crystallinity. The dielectric property indicates the amount of charge that can be stored by a material and it can be used as an indicator to prove that the increase in conductivity is due to an increase in the charge carriers or free mobile ions. If dielectric property of the material increases, the amount of charge stored by the material will also increase. The dielectric response is generally described by the complex permittivity ε* = ε′ − iε″, where real ε′ and imaginary ε″ components are the storage and loss of energy in each cycle of applied electric field. Fig. 7 (a),(b) shows that the values of ε′ and ε″ are very high at low

Assignments

C_O stretching C_O stretching C_C stretching, C\N stretching

1469–1483

CH2 bending or bending O\H

1038–1078 907–943

C_O stretch, C-H and OH bending CO_symmetric stretching

frequency and high temperature but at high frequency these are relatively constant with frequency similar behavior has been observed in a number of polymers [29–33]. Similar results have been reported by Ramya and Hema et al. for PVA and PVP [34]. Such high value of ε′ may be due to the interfacial effects within the bulk of the sample and electrode effects. The variation of ε′ and ε″ with temperature is different for polar and non-polar polymers. In general for non-polar polymers the ε′ and ε″ are independent of temperature but in the case of strong polar polymers the dielectric permittivity increases as the temperature increases. However since the specific volume of the polymer is temperature dependent (i.e.) it increases, as the temperature increases. The dielectric permittivity decreases with increase of temperature in the case of weak polymers. The main advantage of M* formalism is that the electrode effect can be suppressed [35]. Modulus M* has been evaluated using the following relations. 2

2

2

2

M′ = ε′ = ε′ + ε″ and M″ = ε″ = ε′ + ε″

Fig. 8 (a, b) shows that the modulus spectra have an asymmetrical peak. The almost zero values of M′ at low frequency indicate the removal of electrode polarization. The observed long tail at low frequencies is due to the large capacitance associated with the electrodes [36]. The spectrum of M″ shows an asymmetric peak approximately centered in the dispersion region of M″. The modulus peak maximum shifts to higher frequencies and the peak maxima decreases with increase of temperature suggesting the presence of more than one type of relaxation mechanisms [37]. 5. Conclusion PVA–PVP polymer blend electrolyte has been prepared by solution casting technique using DMSO as solvent. The increase in amorphous nature of the polymer electrolytes has been confirmed by XRD analysis. The FTIR analysis reveals that the interchain hydrogen

Table 2 Conductivity for different concentrations of PVA and PVP at different temperatures. Temperature (K) 308 323 343 363 373

Conductivity σ (S cm− 1) 50:50

60:40

70:30

80:20

90:10

1.07 × 10− 07 5.01 × 10− 07 2.81 × 10− 06 1.14 × 10− 05 1.86 × 10− 05

5.24 × 10− 07 2.04 × 10− 06 8.91 × 10− 06 2.13 × 10− 05 3.09 × 10− 05

1.58 × 10− 06 4.89 × 10− 06 1.51 × 10− 05 3.89 × 10− 05 5.49 × 10− 05

2.29 × 10− 07 9.77 × 10− 07 4.26 × 10− 06 1.02 × 10− 05 1.38 × 10− 05

2.04 × 10− 07 1.02 × 10− 06 3.80 × 10− 06 1.04 × 10− 05 1.47 × 10− 05

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Table 3 The activation and regression value for different PVA blends with PVP concentration (from Arrhenius plot). PVA:PVP concentration

Activation energy (Ea)

Regression value

50:50 60:40 70:30 80:20 90:10

0.78 0.61 0.53 0.62 0.64

0.997 0.993 0.998 0.991 0.992

bonding within a PVA–PVP blend occurs between carbonyl groups on PVP and hydroxyl groups on PVA. The dielectric permittivity (ε*), and modulus (M*), are calculated from the ac impedance spectroscopy in the frequency range 42 Hz–1 MHz and the temperature range 308– 373 K. The maximum conductivity has been found to be 1.58 × 10 − 6 S cm − 1 at room temperature for 70PVA:30PVP concentration. The conductivity is increased to 5.49 × 10 − 5 S cm − 1 when the temperature is increased to 373 K. The values of ε′ and ε″ are very high at low frequency and high temperature but at high frequency these are constant with frequency. This is may be due to the interfacial effects within the bulk of the sample and the electrode effects. The activation energy of the all samples was calculated using the Arrhenius plot and it has been found to be 0.53 eV to 0.78 eV. References [1] C.S. Reddy, H. Xia, Z. Quan-yao, M. Li-Qianf, W. Chen, Microelectron. Eng. 83 (2006) 281–285. [2] K.M. Abraham, M. Alamgir, Electrochem Soc 137 (1990) 1657. [3] M. Alamgir, R.D. Moulton, K.M. Abraham, in: K.M. Abraham, M. Salomon (Eds.), Primary and Secondary Lithium Batteries, Electrochem Soc, Pennington, 1991, p. 131. [4] L.Z. Fan, X.L. Wang, F. Long, X. Wang, Solid State Ionics 179 (2008) 1772.

[5] K.M. Abraham, M. Alamgir, Chem. Mater. 3 (1991) 339. [6] K.M. Abraham, Applications of Electroactive Polymers, Chapter 3, in: B. Scorsati (Ed.), Chapman and Hall, London, 1993. [7] F. Croce, F. Bonino, S. Panero, B. Scrosati, Philos Mag B 59 (1989) 161. [8] A. Camposeo, E. Mele, L. Persano, D. Pisignano, R. Cingolani, Phys. Rev. B 73 (2006) 165201. [9] B.K. Choi, Y.W. Kim, H.K. Shin, Electrochemica Acta 45 (2000) 1371. [10] Nam-Soon Choi, Lee Young-Gi, Park Jung-Ki, Ko Yang-Myoun, Electrochim. acta 46 (2001) 1581. [11] S. Ramesh, A.H. Yahaya, A.K. Arof, Solid State Ionics 52–153 (2002) 291. [12] R. Baskaran, S. Selvasekarapandian, N. Kuwata, J. Kawamura, T. Hattori, Solid State Ionics 177 (2006) 2679–2682. [13] M. Sivakumar, R. Subadevi, S. Rajendran, H.C. Wu, N.L. Wu, Eur. Polym. J. 43 (2007) 4466–4473. [14] R.J. Hefford, Polymer 25 (1984) 979–986. [15] S. Navarro Cassu, M.I. Felisberti, Polymer 40 (1999) 4845–4851. [16] S. Gopal, S.A. Agnihotry, V.D. Gupta, Sol. Energy Mater. Sol. cells 44 (1996) 237–250. [17] S. Rajendran, M. Sivakumar, R. Subadevi, Matter. Lett. 58 (2004) 641. [18] H.M. Ragab, Physics B (2010), doi:10.1016/j. Physb.2010.11.030. [19] V. Grigoras, V. Barboiu, Revue Roumaine de chimie 53 (2) (2008) 127–131. [20] M. Abdelaziz, E.M. Abdelrazek, Physica B 390 (2007) 1. [21] C.M. Laot, E. Maramd, H.T. Oyama, Polymer 40 (1999) 1095. [22] X. Li, S.H. Goh, Y.H. Lai, A.T.A. Wee, Polymer 41 (2000) 6563. [23] E.M. Abdelraxek, I.S. Elashmawi, H.M. Ragab, Physica B 403 (2008) 3097. [24] K.H. Wu, Y.R. Wang, W.H. Hwu, Polym. Degrad. Stab. 79 (2003) 195. [25] A. Arvind, S.L. Agrawal, Solid State Ionics 178 (2007) 951. [26] B.A. Boukamp, Solid State Ionics 20 (1986) 301. [27] J.R. Macdonald, Impedance Spectroscopy, Johnwiley & sons, Newyork, 1987, pp. 12–23. [28] J. Kawamura, R. Sato, S. Mishna, M. Shimoji, Solid State Ionics 25 (1987) 155. [29] P.K.C. Pillai, P. Khurana, A. Tripattan, J. Mater. Sci. Lett. 5 (1986) 629–632. [30] R. Vijayalakshmi Rao, M.H. Sridhar, Mater. Lett. 55 (2002) 34–40. [31] P. Dutta, S. Biswas, D. Subodhkumar, Mater. Res. Bull. 37 (2002) 193–200. [32] Moon Gyu Han, Seung Soon Im, J. Appl. Poly. Sci. 83 (2001) 2760–2769. [33] L.V. Karabanova, G. Boiteux, O. Gain, G. Seytre, L.M. Sergeeva, E.D. Lutsyk, P.A. Bondaranko, J. Appl, Polym. Sci 90 (2003) 1191–1201. [34] M. Hema, S. Selvasekarapandian, G. Hirankumar, Ionics 13 (2007) 483–487. [35] Yu.Suzhu, P. Hing, Hu, Xiao, J. Appl. Phys. 88 (2000) 395–404. [36] S. Ramesh, A.K. Arof, Mater Sci.Eng. B 85 (2001) 11–15 2001. [37] R. Mishra, N. Baskaran, P.A. Ramakrishnan, K.J. Rao, Solid State Ionics 112 (1998) 261–273.