Molecular motion studies in VC:VAc copolymer thin films

Abstract

Abstract Depolarization current characteristics of vinyl chloride-vinyl acetate (VC:VAc) copolymer thin films were studied as a function of the polarizing field EP (96.25 × 105-2.25 × 106 V/m), time tp (7.20 × 103—5.04 × 104 sec), and the temperature of polarization Tp (305—425 K). Three relaxation processes at 340, 412, and 460 K were observed with activation energies U of 0.59, 1.01, and 1.37 eV, 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 the space charge polarization, the space charge being the resultant of injected charge carriers from the electrodes and the already present carriers. The peaks at 340 and 412 K shift toward higher temperatures and their U increase with increase of tp and Tp. This is attributed to a distribution of 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. The calculated values of dielectric loss ϵ” from the TSD spectra are in good agreement with those determined from the DC measurements.