Nonlinear conductivity of aqueous electrolytes: beyond the first Wien effect

TL;DR

This paper investigates how high electric fields affect electrolyte conductivity, revealing that water molecule alignment suppresses the Wien effect in concentrated solutions, with theoretical and simulation results showing anisotropic water behavior impacts ionic transport.

Contribution

It introduces a model combining molecular dynamics and stochastic density field theory to explain nonlinear conductivity beyond the first Wien effect in aqueous electrolytes.

Findings

Water molecule alignment reduces the Wien effect in concentrated electrolytes.

Anisotropic permittivity of water influences ionic correlations.

Theoretical predictions qualitatively match simulation results.

Abstract

The conductivity of strong electrolytes increases under high electric fields, a nonlinear response known as the first Wien effect. Here, using molecular dynamics simulations we show that this increase is almost suppressed in moderately concentrated aqueous electrolytes due to the alignment of the water molecules by the electric field. As a consequence of this alignement, the permittivity of water decreases and becomes anisotropic, an effect which can be measured in simulations and reproduced by a model of water molecules as dipoles. We incorporate the resulting anisotropic interactions between the ions into a Stochastic Density Field Theory and calculate ionic correlations as well as corrections to the Nernst-Einstein conductivity, which are in qualitative agreement with the numerical simulations.