Correlated Ion Transport and the Gel Phase in Room Temperature Ionic Liquids

TL;DR

This paper develops a theory linking ion aggregation to gelation in room temperature ionic liquids and validates it with molecular dynamics simulations, revealing the potential for a gel phase in RTILs affecting ion transport.

Contribution

It introduces a new theoretical framework for ion aggregation and gelation in RTILs, validated by simulations, and explores the existence of a gel phase in these liquids.

Findings

Large ion clusters can form and percolate, creating a gel phase.

The theory accurately predicts cluster distributions across various RTILs and temperatures.

A gel phase in RTILs could significantly impact their ion transport properties.

Abstract

Here we present a theory of ion aggregation and gelation of room temperature ionic liquids (RTILs). Based on it, we investigate the effect of ion aggregation on correlated ion transport - ionic conductivity and transference numbers - obtaining closed-form expressions for these quantities.The theory depends on the maximum number of associations a cation and anion can form, and the strength of their association. To validate the presented theory, we perform molecular dynamics simulations on several RTILs, and a range of temperatures for one RTIL. The simulations indicate the formation of large clusters, even percolating through the system under certain circumstances, thus forming a gel, with the theory accurately describing the obtained cluster distributions in all cases. We discuss the possibility of observing a gel phase in neat RTILs, which has hitherto not been discussed in any detail.