Relaxation processes of polar molecules in some organic glasses

Abstract

Dielectric absorption studies of a variety of polar solutes containing rotatable groups and of some analogous rigid molecules dispersed in (i) an atactic polystyrene matrix, (ii) glassy o-terphenyl and polyphenyl ether have been carried out. Sample preparations and the dielectric measurements using General Radio 1615-A and 1621 capacitance bridges with appropriate temperature-controllable cells have been described. The glass transition temperature measurements using the Glass Transition Temperature Measurement Apparatus have also been described. The experimental data as a function of frequency at different temperatures were subject to analysis by a series of computer programmes written in APL language. The activation energy barriers opposing the dielectric relaxation processes were obtained by the application of the Eyring rate equation. Different types of polar rigid molecules have been studied mainly to provide sources of relaxation data and activation parameters in the three media for comparison with those of flexible molecules of analogous size. The results of these rigid molecules have been used to obtain a correlation between enthalpy and entropy of activation; enthalpy of activation and volume needed for the reorientation of the rigid molecules. The activation parameters for the rigid molecules were found to depend on the nature of the solvent.