Reversible Ionic Aggregation Kinetics in Concentrated Electrolytes

TL;DR

This paper introduces a formalism for reversible ionic aggregation kinetics in concentrated electrolytes, linking equilibrium theories with dynamic rate equations and validating with molecular dynamics simulations.

Contribution

It develops a novel macroscopic rate equation framework based on the reversible Smoluchowski aggregation equation for electrolytes.

Findings

Qualitative agreement with molecular dynamics simulations

Identification of multiple timescales in ionic aggregation dynamics

Potential to explore non-Newtonian and confinement effects

Abstract

Here we develop a formalism for reversible ionic aggregation kinetics in an example concentrated electrolyte, building on previous equilibrium work of McEldrew and co-workers, and thermoreversible polymers and patchy particle systems. This is achieved through solving a macroscopic rate equation of open/occupied association sites, shown to be a solution of the reversible Smoluchowski aggregation equation, which predicts how ionic associations in electrolytes change subject to a step-change in conditions. We test the derived equations against atomistic molecular dynamics simulations of a salt-in-ionic liquid, where good qualitative agreement is obtained, but quantitative differences are found. This highlights the multiple time scales that exist in concentrated electrolytes, with a fast timescale preceding a longer timescale. We hope this formalism opens new avenues in understanding the dynamics and non-equilibrium behaviour in electrolytes. For example, the formalism can be developed further to investigate the non-Newtonian behaviour of concentrated electrolytes, double layer charging, and the slow dynamics of these electrolytes in confinement.