Abstract
The temperature and the electric-field dependences of the dielectric relaxation have been investigated in amorphous poly(ethyl methacrylate) (PEMA) thin films by using the thermally stimulated discharge current (TSDC) and the thermal sampling (TS) techniques and AC dielectric measurements. All measurements were performed on cast thin films with thicknesses of 50 - 60 µm over a temperature range covering the glass transition region (α-relaxation). The nature of relaxation mechanisms in amorphous PEMA is discussed on the basis of the TSDC and dielectric results. Comparative studies of the dielectric properties obtained by using the TSDC indicated a strong resemblance between the two techniques. PEMA films are characterized by two TSDC relaxation peaks, revealing the presence of two major relaxation processes and termed as the α-peak, around 341 K, and the β-peak ranging from 385 K to the 403 K, associated with dipolar relaxation and space charge relaxation processes, respectively. The thermal sampling technique (TS) was used to resolve the complex TSDC behavior of the films to obtain the elementary peaks characterized by the Debye relaxation time. The dependence of the peak temperature Tm on the polarizing temperature Tp indicated a continuous distribution of relaxation times. The activation parameters characterizing the TS peaks, such as the activation energy (E), the pre-exponential factor (τ0) and the dipole-dipole interaction strength parameter (di), have been estimated by using a modified approach of the TSDC theory with the dipole-dipole interaction effect and two relaxation models, the Arrhenius (DDIAR) and the Vogel-Tamman-Fulcher (DDIVTF) relaxation models. Good results were obtained in comparison with other methods such as the initial rise method. A linear relationship between the activation enthalpy (ΔH) and activation entropy (ΔS) of the α-relaxations was obtained, confirming the validity of the compensation law. KCI Citation Count: 2