Dielectric properties and a.c. electrical conductivity of aqueous solution grown pure and iodine doped poly (vinyl alcohol) films

摘要

Poly vinyl alcohol (PVA) films of uniform thicknesses 280, 120, 80, 50 and 25 microns, and also 50 micron PVA films doped with 4, 3, 2 and 1 wt percent iodine of PVA weight in aqueous solution have been prepared by solution grown technique. Ag-PVA-Ag sandwich structures of film capacitors have been fabricated for their dielectric characterization. The capacitance and dissipation factor of these capacitors are measured in the frequency range 100 Hz-100 kHz at 25 deg C. The dielectric permittivity epsilon', loss epsilon", and a.c. conductivity sigma, have been determined using the measured values of capacitance and dissipation factor. It is found that the value of epsilon' decreases with increase in frequency and increases with the film thickness while dielectric loss epsilon" shows marked variation with frequency. For iodine doped films, values of epsilon' and epsilon" vary anomalously with the increase in concentration of iodine. From the a.c. conduction studies, it is observed that the a.c. conductivity of pure PVA films increases with the film thickness and vary almost linearly with frequency in the range of 10~(-11) - 10~(-8) S cm~(-1). Further it is found that there is anomalous variation in conductivity of iodine doped PVA film with increase in iodine concentration. From these dielectric studies, it seems that an increase in epsilon' and epsilon" with the increase in PVA film thickness is due to the residual water or variation in degree of syndiotacticity of PVA chain. In case of iodine doped PVA films, the variations in crystalline and complex formation of PVA molecules with iodine are responsible to change the dielectric parameters.