Electric Strength and Liquid Structure

Abstract

Recent work on the electric strength of pure hydrocarbon liquids has shown that the strength is probably determined by the amount of energy lost by conduction electrons exciting molecular vibrations by collisions while moving under the applied field through the liquid. The strength can then be determined in terms of a mean free path for the collisions involved. The present paper attempts to show that the liquid structure, i.e., the molecular arrangements in the liquid phase, is also influencing the strength, and this is illustrated by measurements of the temperature effect on the strength of some n-paraffins, the molecules of which are known to pack with their long axes parallel producing a degree of anisotropy. Distinct breaks in the electric strength vs temperature characteristics are found, even when density changes are accounted for, and these occur at temperatures which are in very good agreement with similar breaks in the characteristics of other properties such as density, viscosity, and heat capacity. These breaks have already been associated with changes in liquid structure from quasi-crystallinity to molecular libration (245°K) and from molecular libration to free rotation (288–353°K). If molecular orientation takes place in the applied field then the electron energy loss will be different in the three liquid ``phases'' and would account for the observed transitions in the breakdown characteristics.