On analytical theories for conductivity and self-diffusion in concentrated electrolytes

TL;DR

This paper reviews and extends analytical theories, particularly Stochastic Density Field Theory, to better describe conductivity and self-diffusion in concentrated electrolytes, addressing technical challenges and comparing with existing approaches.

Contribution

It introduces improved approximations for electrolyte transport properties within SDFT and compares them to traditional theories, enhancing understanding of concentrated electrolyte behavior.

Findings

Short-range Coulomb interaction truncations impact property predictions.

Enhanced treatment of hydrodynamic effects improves SDFT accuracy.

Comparison guides future extensions of SDFT for electrolytes.

Abstract

Describing analytically the transport properties of electrolytes, such as their conductivity or the self-diffusion of the ions, has been a central challenge of chemical physics for almost a century. In recent years, this question has regained some interest in light of Stochastic Density Field Theory (SDFT) -- an analytical framework that allows the approximate determination of density correlations in fluctuating systems. In spite of the success of this theory to describe dilute electrolytes, its extension to concentrated solutions raises a number of technical difficulties, and requires simplified descriptions of the short-range repulsion between the ions. In this article, we discuss recent approximations that were proposed to compute the conductivity of electrolytes, in particular truncations of Coulomb interactions at short distances. We extend them to another observable (the self-diffusion coefficient of the ions) and compare them to earlier analytical approaches, such as the mean spherical approximation and mode-coupling theory. We show how the treatment of hydrodynamic effects in SDFT can be improved, that the choice of the modified Coulomb interactions significantly affects the determination of the properties of the electrolytes, and that comparison with other theories provides a guide to extend SDFT approaches in this context.