Some dielectric studies of molecular and intramolecular motions

Abstract

Dielectric relaxation studies of a series of polar diaryl molecules and of some analogous rigid molecules dispersed in atactic polystyrene and poly(vinyltoluene) have been carried out. Preparation of both polymer matrices and the dielectric measurements using a General Radio 1615-A capacitance bridge and a Hewlett-Packard Q-meter with appropriate temperature-controllable cells have been described. The experimental data as a function of frequency at different temperatures were subjected to analysis by a series of computer programmes written in the APL language. The activation energy barriers for the dielectric relaxation processes were obtained by the application of the Eyring rate equation. A number of polar rigid molecules has been studied to provide a wide background knowledge of relaxation and activation parameters for comparison with those of flexible molecules of analogous size. Attempts have also been made to correlate the molecular relaxation absorptions by classification of the polar rigid molecules into three categories in terms of their dipole positions. It is apparent from the present study that the inclination of the molecular dipole to the principal axes may be a factor in determining the magnitude of the observed relaxation time and the activation parameters and this is in line with what was previously found by investigations in the liquid state. To this end. studies have been made of some disc-llke molecules such as 9-bromoanthracene and 9-bromophenanthrene. Comparison of their Eyring analysis results with the other elongated molecules showed that the molecules exhibited different contributions for rotation about the principal axes...