Self-Consistent Description of Vapor-Liquid Interface in Ionic Fluids

TL;DR

This paper develops a theoretical framework to accurately describe the vapor-liquid interface in ionic fluids, accounting for ion correlations and asymmetry, with results matching simulation data and providing new insights into interfacial structures.

Contribution

It introduces a modified Gaussian renormalized fluctuation theory that captures both short-range and long-range ion correlations at interfaces, including asymmetric salts.

Findings

Quantitative agreement with simulation data for symmetric salt.

First theoretical prediction of interfacial structure for asymmetric salt.

Highlights importance of local charge separation in interfacial phenomena.

Abstract

Inhomogeneity of ion correlation widely exists in many physicochemical, soft matter, and biological systems. Here, we apply the modified Gaussian renormalized fluctuation theory to study the classic example of the vapor-liquid interface of ionic fluids. The ion correlation is decomposed into a short-range contribution associated with the local electrostatic environment and a long-range contribution accounting for the spatially varying ionic strength and dielectric permittivity. For symmetric salt, both the coexistence curve and the interfacial tension predicted by our theory are in quantitative agreement with simulation data reported in the literature. Furthermore, we provide the first theoretical prediction of interfacial structure for asymmetric salt, highlighting the importance of capturing local charge separation.