Depolarization current studies of vinyl chloride-vinyl acetate copolymer thin films

Abstract

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 × 10 5−2.25×10 6 V m −, time (7.20 × 10 3−5.04×10 4 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 3.66×10 3, 8.78×10 6 and 1.46×10 10 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.