Mechanical and Dielectric Relaxations in Paraffin Crystals

Abstract

Real and imaginary parts of longitudinal wave modulus at 1/3, 1, and 3 Mc/s and shear modulus at 1 Mc/s and 33 kc/s are measured for normal paraffin crystals of three different carbon numbers at temperatures from 20° to -60°C. Dielectric constant and loss in oxidized paraffins are measured in the same temperature range as a function of frequency (30 c/s–1 Mc/s). The crystalline dispersion is observed at temperatures several tens of degrees below the melting point. The activation energy is the same for mechanical and dielectric dispersions, which indicates that oxidation of paraffins gives essentially no influence upon the nature of molecular motion. The relaxation strength increases with increasing temperature for each sample. The mechanical relaxation strength increases with increasing carbon number when compared at the same temperature. The above behavior is quantitatively explained in terms of Okano's theory in which the crystalline dispersion is assumed to come from incoherent torsional vibrations of chain molecules in the crystal. The density of polar groups in oxidized paraffins estimated by the theory of the dielectric relaxation strength agrees in the order of magnitude with that determined from infrared absorption.