Electrochemical Preparation and Characterization of Polypyrrole-Polyethylene Glycol Conducting Polymer Composite Films Anuar Kassim, Ph.D. *, H.N.M. Ekarmul Mahmud, Ph.D., Lim Mei Yee, M.Sc., and Nurain Hanipah, B.Sc. Department of Chemistry, Faculty of Science, Universiti Putra Malaysia. 434000 Serdang, Selangor, Malaysia. * E-mail: anuar@fsas.upm.edu.my ABSTRACT The electrochemical preparation of polypyrrolepolyethylene glycol (PPy-PEG) conducting polymer composite films on an indium tin oxide (ITO) glass electrode from an aqueous solution containing pyrrole monomer, p-toluene sulfonate (p-ts) dopant and polyethylene glycol (PEG) insulating polymer is reported in this paper. The conductivity of the prepared composite films was found to vary with the increase in p-ts concentration in the pyrrole solution. The characterization by Fourier transform infrared spectroscopy (FT-IR) shows the successful incorporation of PEG into the polypyrrole structure forming PPy-PEG polymer composite films. The broad peaks in X-ray diffraction revealed that PPy-PEG composite films are amorphous. The optical microscopic results show the morphological changes of the prepared composite films. (Keywords: conducting polymer, polypyrrole, polyethylene glycol, p-toluene sulfonate.) INTRODUCTION Conducting polymers can exhibit significant levels of electrical conductivity suitable for use in electronic devices, batteries, functional electrodes, electrochromic devices, optical switching devices, sensors, and so on [1 5]. Research interest in the development of conducting polymers such as polyaniline, polypyrrole, polythiophene, polyphenylene, etc. has increased tremendously because of the versatility of their applications. Attempts have been made to produce composites or blends of conducting polymer films with some insulating polymer in order to overcome the drawbacks such as poor processability and the lack of essential mechanical properties exhibited by these polymers [6]. In this technique, a host of insulating polymers, namely, poly(vinylalcohol) [6,7], poly(styrenesulphonate) [8], polycarbonate [9], poly(methyl methacrylate) [10], rubber [11], polyimide [12], etc., have been combined with a number of conducting polymers such as polypyrrole, polyaniline, polythiophene, etc., in aqueous or organic medium to produce conducting polymer composites which will have the conducting properties of the conducting polymer with some of the superior mechanical properties of the host insulating polymer. Polypyrrole (PPy) is one of the most studied conducting polymers because of its rather straightforward preparation methods [13]. PPy materials are reasonably stable in air, present high conductivity, good electrochemical properties, and thermal stability and are easily generated both chemically and electrochemically [14]. Polypyrrole conducting polymers exhibit a wide range of surface conductivities (10 3 S cm 1 < σ < 100 S cm 1 ) depending on the functionality and substitution pattern of the monomer and the nature of the counter ion or dopant [15]. However, the principal problems with the practical utilization of conducting polymers like polypyrrole include its poor mechanical properties like brittleness and low processibility [16]. Blending insulating polymers is an attractive route to improve their mechanical properties without loosing their conductivity [17]. In this paper, the authors wish to report on the electrochemical preparation and characterizations of the composite films of PPy-PEG conducting polymer as there are no reports available on the PPy-PEG conducting polymer composite films in the literature. The Pacific Journal of Science and Technology 103
EXPERIMENTAL DETAILS The pyrrole monomer (Fluka) was first purified by distillation at 131 C and, thereafter, stored and refrigerated until use. Polymerization was then performed electrochemically in a threecompartment cell, using a potentiostat (Model PS 605, USA). A conductive indium-tin oxide (ITO) glass was used as the working electrode with a carbon rod as the counter electrode. All potentials were referred to a saturated calomel electrode (SCE). An aqueous solution containing 0.2 M pyrrole, 0.05 M 0.3 M p-toluene sulfonate and 0.2 % PEG was used to prepare PPy-PEG conducting polymer composite films. The composite films were grown potentiostatically at 1.2 V (versus SCE) for a fixed time of 2 hours. The composite films thus produced on the ITO glass surface as an insoluble film were rinsed thoroughly with distilled water and then peeled off from the electrode. It was then dried in the oven at 60 C for 24 hours. The electrochemically prepared PPy-PEG conducting composite films were characterized by conductivity measurement, FT-IR, X-ray diffraction and optical microscopy. The electrical conductivity of the PPy-PEG composite films was measured by four-point probe technique. The FT-IR absorption spectra of the composite films were recorded on Perkin Elmer FT-IR spectrophotometer. The X-ray diffractions of the composite films were analyzed by Philip PW-1390 diffractometer. The optical micrographs of the composite films were taken using an inverted trinocular microscope. RESULTS AND DISCUSSION Conductivity The electrical conductivity of the prepared polypyrrole-polyethylene glycol (PPy-PEG) conducting polymer composite films was measured at room temperature by four-point probe technique, taking the average value of several readings at various points of the composite films. The highest conductivity of PPy-PEG composite films measured at room temperature was found to be 61.3 S/cm for the film prepared from 0.2 M pyrrole with 0.2 % PEG and 0.1 M p-ts. The conductivity was found in the range of 61.3 S/cm to 23.6 S/cm with the different concentrations of p-ts used to prepare the composite films (Figure 1). Generally, the existence of dopant (p-ts) may cause the creation of positively charged polypyrrole, more electron holes available for longer polymer chain, and more co-planarity between interchains, which all are favorable for a higher conductivity performance. The existence of too much dopant (p-ts) can disturb the polymerization and cause low conductivity. Figure 1 shows the changes in conductivity of the composite films with the increase in p-ts concentration used to prepare the composite films. Conductivity-S/cm) 70 60 50 40 30 20 10 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 Concentration of p -TS (M) Figure 1: Variation of Electrical Conductivity of PPy-PEG Composite Films with the Concentration of p-ts (dopant) used to prepare the Films. FT-IR Study The infrared absorption spectrum of polypyrrolepolyethylene glycol (PPy-PEG) composite film is shown in Figure.2. The broad strong bands between 3440 3424 cm -1 corresponds to the stretching vibrations of the intra-molecular hydrogen bond (υ O-H ) of PEG and this frequency also shows the absorption of N H stretching of polypyrrole. The frequency at 2916 cm -1 refers to the stretching vibration of C H bond. The absorption at 1626 cm -1 was assigned to the C=C ring stretching of pyrrole. The band at 1380 cm -1 is due to C H vibrations. The Pacific Journal of Science and Technology 104
120 100 400 % Transmittance 80 60 40 20 0 3900 3400 2900 2400 1900 1400 Wavenumber, cm -1 900 400 Intensity a.u.) 300 200 100 Figure 2: FT-IR Spectrum of PPy-PEG Composite Film. The peak at 1136 cm -1 is due to C-C stretching. The peak at 1080 cm -1 corresponds to the inplane deformation of O-H group and C-O symmetric stretching of PEG. The band at 1020 cm -1 is due to in-plane deformation of C H bond and N H bond of pyrrole ring. X-RD Study From the X-RD analysis of the PPy-PEG composite film, it can be seen that the film exhibited broad scattering peaks at 2θ value around 25 and 10 respectively, which suggest that the PPy-PEG composite films are virtually amorphous. Previous X-ray scattering studies of polypyrrole films have been reported to be highly disordered and non-crystalline [18]. Figure 3 shows the X-RD diffractogram of PPy-PEG conducting polymer composite film. Optical Microscopic Study The morphological study on polypyrrolepolyethylene glycol (PPy-PEG) composite films shows globular morphology for the film facing the solution side (Figure 4). The electrode side of the film surface appeared much smoother compared to the solution side surface. This is due to the fact that the polymerization was initiated on the electrode side and proceeded towards the solution side with the reaction time making the polymer film thicker with rough globules on the surface of solution side. 0 0 5 10 15 20 25 30 35 Figure 3: X-ray Diffraction Pattern of PPy-PEG Composite Film Prepared from 0.2 M Pyrrole, 0.1 M p-ts and 0.2 % PEG. The surface morphology of the electrode side shows that the surface was smooth. There was no phase separation apparent either on the electrode side or on the solution side of the films and thus it supports the homogeneous film formation of polypyrrole with polyethylene glycol. CONCLUSION 2 theta The present communication shows that polypyrrole-polyethylene glycol (PPy-PEG) conducting polymer composite films with very good conductivity can be prepared electrochemically from an aqueous pyrrole solution containing p-toluene sulfonate dopant and polyethylene glycol. The electrical conductivity of the composite films is influenced by the concentration of dopant (ptoluene sulfonate). The FT-IR analysis shows the formation of PPy-PEG composite film. The broad peaks in X-ray diffraction revealed that PPy-PEG composite films are amorphous. The optical micrographs of the composite films exhibit the globular morphology for its solution sides while the electrode sides are rather much smoother. The Pacific Journal of Science and Technology 105
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interests falls in the field of conducting polymers and their applications. Nurain Hanipah, B.Sc. is a researcher at the University Putra Malaysia with research interests in conducting polymers. SUGGESTED CITATION Kassim, A., H.N.M. Ekarmul Mahumud, L.M. Yee, and N. Hanipah. 2006. Characterization of Polypyrrole-Polyethylene Glycol Conducting Polymer Composite Films.. Pacific Journal of Science and Technology. 7(2):103-107. Pacific Journal of Science and Technology The Pacific Journal of Science and Technology 107