Molecular dynamics of a siloxane liquid-crystalline polymer as studied by dielectric relaxation spectroscopy

Abstract

A simple theory of the dielectric relaxation of dipolar mesogenic groups in a liquid-crystal environment is described. It shows that the four relaxation modes which are active in a dielectric relaxation experiment arise from combinations of certain time-correlation functions for the angular motions of the dipolar groups in the nematic potential. Experimental dielectric data for a nematic siloxane polymer are reported for wide ranges of frequency and temperature and for different macroscopic alignments of sample (homeotropic, planar). These data are analysed with the aid of the theory, and it is shown that the director order parameter S_d, the local order parameter S and the dipole moment ratio µ_l/µ_t may be determined using combinations of data for samples having different extents of macroscopic alignment.