Journal of the Korean Physical Society

pISSN 0374-4884 eISSN 1976-8524
Qrcode

Article

J. Korean Phy. Soc. 2010; 57(2): 272-281

Published online August 13, 2010     https://doi.org/10.3938/jkps.57.272

Copyright © The Korean Physical Society.

Relaxational Study of Poly(Ethyl-mthacrylate) by Thermally Stimulated Depolarization Current, Thermal Sampling Spectroscopy: Modified Dipole-Dipole Interaction Theory

M T Ahmed

Abstract

The temperature and electric field dependence of dielectric relaxation has been investigated in amorphous poly(ethyl methacrylate) (PEMA) thin films using thermally stimulated discharge current (TSDC) as well as thermal sampling (TS) techniques and AC dielectric measurements. All measurements were performed on a cast thin film of thickness 50 -60 탆 over a temperature range cover the glass transition region (??-relaxation).The nature of relaxation mechanisms in amorphous PEMA is discussed on the basis of TSDC and dielectric results. The comparative studies of dielectric properties with TSDC indicated a strong resemblance between the two techniques. PEMA 쟣ilms are characterized by two TSDC relaxation peaks, reveal the presence of two major relaxation processes termed as 젰?peak around 341 K and ??-peak ranging from (385 K?to 403 K), associated with dipolar relaxation and space charge relaxation processes, respectively. Thermal sampling technique (TS) was used to resolve the complex TSDC behavior of films to obtain its elementary peaks characterized by a Debye relaxation time. The observed of the peak temperature Tm on polarizing temperature Tp, indicating a continuous distribution of relaxation times. The activation parameters characterizing the TS peaks such as activation energy (E), pre-exponential factor (??0) and dipole-dipole interaction strength parameter (di) have been estimated by using the modification approach of the TSDC theory with dipole-dipole interaction effect using two relaxation models, in Arrhenius (DDIAR) and in Vogel-Tamman-Fulcher (DDIVTF) relaxation models. Good results are obtained in comparison with other methods such as initial rise method. 잸 linear relationship between the activation enthalpy (?H) and activation entropy (?S) of the ??-relaxations is obtained, confirming the validity of the compensation law.

Keywords: Relaxation processes,, poly(ethyl methacrylate),, Dipolar relaxation,, Arrhenius (DDIAR) and in Vogel-Tammann-Fulcher (DDIVTF) relaxation models,, Compensation., Entropy,, Enthalpy,, , Thermally stimulated discharge current (TSDC),, Thermal sampling (TS),