Dielectric Behavior and Crystal Structure of Ethyl and Vinyl Stearate

Abstract

Measurements of the real (ε′) and imaginary (ε″) components of the complex dielectric constant have been made on ethyl and vinyl stearate and on mixtures of ethyl stearate in n-heneicosane at temperatures from +60° to —80°C and over a frequency range from 100 to 50 000 cps. A relaxation dispersion region, which was similar in shape and position for all samples, occurred below 0°C for the frequency range considered here. The magnitudes of the dispersions were found to be greater the more quickly the samples were frozen, and very much reduced for samples crystallized from acetone. Annealing of the solid samples at temperatures as low as 20 centigrade degrees below the freezing points resulted in a gradual decrease in polarization. Cooling curve data was obtained in order to supplement the above work. The results suggest that the molecular rotations involved in the observed solid state dispersions are associated with metastable crystal structures and that, in particular, the decrease in polarization with time is due to a gradual transformation in parts of the sample from a vertical to a tilted crystal structure.