Dielectric Relaxation Studies in the Solid Phase Nematic Crystal

Abstract

Dielectric measurements have been made in the stable and metastable solid modifications of p-(p-Ethoxyphenylazo)phenyl Hexanoate (EPPH) in the frequency range 0.5 to 100 KHz and in the temperature range 103 to 273° K. The dielectric dispersion was absent in the stable modification while in the metastable modification, obtained by rapid cooling, a clear Debye-type dispersion with symmetric distribution of relaxation times was obtained at temperatures above about 198° K. The plots of dielectric relaxation strength δε (=ε₀ - ε_∞) and distribution parameter a vs. reduced temperature (T/T _{dipale-freezing}) exhibit the similar behaviour as for EBBA [Mol. Cryst. Liq. Cryst., 45, 117 (1978)] which indicates that the dielectric dispersion observed in the present study is due to the hindered rotation of ethoxy groups which remain active (with an activation energy of 7 K. cal/mole) in the low temperature region.