Dielectric properties of electrolyte solutions. Lithium perchlorate solutions in tetrahydrofuran + benzene mixtures

Abstract

For electrolyte solutions in weakly polar solvents, the collective motion of ions can give rise to an ionic relaxation process in addition to the molecular one. The former is described by a model involving a Brownian linear motion of the ions between collisions. The corresponding part of the complex permittivity is given an analytical form characterized by an asymmetrical distribution of relaxation time. Measurements have been made, between 137 MHz and 34 GHz, on LiClO₄ solutions in tetrahydrofuran + benzene mixtures. The data have been analysed according to a new statistical procedure which leads to a straightforward separation between ionic and molecular relaxation. The former supports the above description of the dynamic state of the solute. In particular, the magnitude of the average time between collisions, derived from the dielectric data, compares well with the theoretical value calculated from the viscosity of the solution by means of the Stokes–Einstein formula.