STUDIES OF THE ELECTRONIC AND DIELECTRIC PROPERTIES OF POLYMERS WITH SPECIAL REFERENCE TO CELLULOSE ACETATE

Abstract

The most traditional involvement of polymers in electrical application has been to Inhibit electrical conduction. Only, recently, their capabilities to perform as active elements have been recognised and they now show promises for various electrical and electronic devices. However, for utilizing the potential of these materials to meet the specific technological objectives, one demands an understanding of the electronic and di-electric properties of polymers. And this forms the topic of the present thesis. In polymers, the electrical phenomenon is found much complex and could not be explained on the basis of existing theories. A whole gamut of experimental and theoretical work is necessary to elucidate the basic conceptsinvolved. Increasing attention is now being devoted in this direction. The interest is also a conse-quence of the growing need for large area electronic devices, where the polymers have immense prospects. Low cost and easy fabrication are the advantages with polymers which also make theth important for ammercinl applications. The attempt through the investigations contained in this thesis has been to understand the electrical behaviour of polymers with special reference to cellulose acetate. However, no pretence towards the completeness of the presented work is made and the area is still open. A short account of the present studies is given below. As for the plan of the thesis, Chapter I develops the present concepts and trends needed to understand the Electronic and dielectric properties of polymers together with the current status of these materials. An outline of the scope of present work and motivation for carrying out the same is also included in this chapter. Chapter II contains the details of the sample preparation and the various measurement., techniques employed in the present studies. Design and development of experimental set-ups for the different studies are also briefly described. Besides, the results of X-ray investi-gations on pure and iodine doped cellulose acetate are also given in this chapter. Chapter III deals with the steady-state conduction current measurements performed on pure and iodine doped cellulose acetate films. The current-voltage characteris-tics have been studied as a function of dopant concentra-tion, thickness and temperature. Space-charge-limited current behaviour has been observed in these samples. The results of the measurements are discussed in view of optical and structural investigations and ,yield the quanti-tative and qualitative information about the charge. transport and trapping parameters. In Chapter TV, the step voltage transient current studies are analysed to identify the carrier migration process, in cellulose acetate films and the results are ii used to determine the carrier mobility. These information are also supplemented with the ac conductivity studies performed at different frequencies and temperatures. The information about the charge carrier transport and generation in cellulose acetate have been obtained from the polarity reversal method of space-charge-limited currents. These studies are the subject of Chapter V. Chapter VI illustrates the thermally stimulated and short-circuit discharge current investigations. These studies provide a diagnostic means for determining the trapping and conduction parameters in cellulose acetate. The studies of the surface potential decay charac-teristics of pure and iodine doped cellulose acetate films are included in Chapter VII. The results are analysed to probe the charge storage and charge transport properties of these samples. An improved theory of surface potential decay in dielectrics has also been presented in this chapter. Chapter VIII is devoted to the spontaneous currents observed in virgin cellulose acetate films. It has been found that the M1-CA:I2-M2 system has a good prospect in the formation of a dry cell.