Electric modulus and AC conductivity studies in conducting PPy composite films at low temperature
Introduction
In recent years, conducting polymer composites and blends have attracted the attention of material researchers, with increasing interest in obtaining properties that are intermediate between those of the homopolymers [1], [2], [3], [4], [5]. Investigation of the electrical properties of these materials is desirable, not only to predict the electrical properties but also to indirectly predict the dynamical behavior. To improve the structural and electrical properties of the composite materials, samples containing conducting polymers like polypyrrole (PPy) and non-conducting polymers like poly(vinyl chloride) [6] or poly(vinyl alcohol) [7] were synthesized.
The study of conductivity relaxation behavior in conducting polymer composite materials has become an interesting area of active research because of their potential applications in solid state devices [8], [9], [10]. A method of predicting the relaxation behavior of composites is the electric modulus theory. The electric modulus spectra, therefore, provide an opportunity to investigate conductivity and its associated relaxation in polymer composites [11], [12]. The purpose of the present work is to prepare and study composite materials containing PPy alloyed with non-conducting ethylene-vinyl alcohol copolymer (EVOH) by immersing EVOH films containing PPy monomer into the oxidant aqueous FeCl3 solution. The frequency-dependent dielectric properties of the conducting composites were investigated at several constant temperatures. By using the electric modulus functions, different effects could be observed.
Section snippets
Materials and preparation of composite films
Pyrrole (Py) monomer was provided by Biomedical ICN, USA. Poly(ethylene vinyl alcohol) (EVOH), (68% vinyl alcohol) was supplied by Poly. Sci. Inc., USA. Reagent grade ferric chloride, FeCl3, obtained from Reidel-de-Haen, AG, Germany, was used as an oxidizing agent for the chemical polymerization of pyrrole. EVOH films were prepared by the casting technique, in which the dissolved EVOH in dimethyl sulfoxide was cast in covered flat glass petri dishes and dried in an oven regulated at 338 K to
Permittivity formalism
The real ε′ and imaginary ε″ parts of dielectric permittivity for composites containing various PPy contents, have been measured at several temperatures between 180 and 300 K. The real ε′ and imaginary ε″ components show a simple frequency dispersion at all temperatures. Only the composite containing 10.8 wt% PPy displayed a relaxation loss as shown in Fig. 1. The relaxation is observed as a gradual decrease in ε′(f) and as a broad peak in ε″(f). This relaxation can also be
Conclusion
The present data show clearly the importance of the electric modulus model when dealing with conducting composites. The electric modulus provides a good qualitative description of the dielectric relaxation. The representation of the dielectric properties in terms of the electric modulus, is very sensitive and the features of relaxation peaks depend on the composite structure. The estimated conductivity relaxation time and energy for different temperatures are close to one another. The
Acknowledgements
The authors acknowledge the assistance of Prof. M.F. Mostafa, Physics Department, Faculty of Science, Cairo University, for the opportunity to carry out the AC measurements in her laboratory.
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