DEPOLARIZATION CURRENT STUDIES OF VINYL CHLORIDE VINYL ACETATE COPOLYMER THIN-FILMS

Depolarization current characteristics of vinyl chloride-vinyl acetate (VC- VAc) copolymer thin films grown from solution by an isothermal immersion technique were studied as functions of the polarizing field (6.25 × 105-2.25×106 V m-, time (7.20 × 103-5.04×104 s), the temperature of polarization (305-425 K), the nature of the vacuum-evaporated electrode metals (gold, copper, silver and aluminium) used during polarization, the thickness of the copolymer fims (4000-10 000 Å) and the heating rates of depolarization (0.033-0.20 K s-1). Three relaxation processes at 340, 412 and 460 K were observed with activation energies of 0.59, 1.01 and 1.37 eV and relaxation times at 300 K of 3.66×103, 8.78×106 and 1.46×1010 s respectively. The peak at 340 K is associated with orientation of the dipoles of the main polymer chain; that at 412 K is attributed to ionic movements in the amorphous region of the VC-VAc copolymer film; and that at 460 K is attributed to release of charge which is the resultant of the charge already present and that due to the injected charge carriers. The peaks at 340 and 412 K shift towards higher temperatures and their activation energies increase with increases in the polarizing time and temperature. This is attributed to a distribution of the relaxation times and activation energies and suggests that these two peaks are complex in nature and cannot be represented by a discrete level of activation energy having a single relaxation time. © 1979.