Transport properties and the time evolution of electrolyte solutions in the Brownian dynamics approximation

Abstract

The method of the brownian dynamics is applied to a 1 M solution of a particular 2–2 electrolyte to generate time dependent configurations. The results are analysed phenomenologically in terms of ion pairs and triplets formation. From the radial distribution functions it is found that the formation of pairs of opposite signs plays a fundamental role in the structure of the solution. The time dependent radial distribution G _+- (r, t) shows that the persistence of this structure is about 10^-11 s. The transport properties (self-diffusion coefficients and electrical conductance) exhibit a small deviation from the Nernst-Einstein relationship which can also be interpreted tentatively in terms of cation-anion clusters. A more detailed analysis of the time evoluation of the different ionic clusters shows that a continuous exchange occurs between the free ions and the ionic clusters and that anion-cation couples have a life span not much longer than that of other types of pairs and triplets.