Field theory for size- and charge asymmetric primitive model of electrolytes. Mean-field stability analysis and pretransitional effects

TL;DR

This paper develops a field-theoretic framework to analyze the stability and phase behavior of size- and charge-asymmetric ionic models, revealing conditions for gas-liquid separation and periodic ordering.

Contribution

It introduces a comprehensive field-theoretic approach for the primitive model of electrolytes across all size and charge asymmetries, identifying key order parameters and phase instabilities.

Findings

Gas-liquid separation occurs for all size and charge asymmetries except when symmetric.

Instabilities towards periodic ionic ordering are also identified.

Two order parameters are related to physical quantities for various asymmetries.

Abstract

The primitive model of ionic systems is investigated within a field-theoretic description for the whole range of size-, \lambda, and charge, Z, ratios of the two ionic species. Two order parameters (OP) are identified, and their relations to physically relevant quantities are described for various values of \lambda and Z. Instabilities of the disordered phase associated with the two OP's are determined in the mean-field approximation. A gas-liquid separation occurs for any Z and \lambda different from 1. In addition, an instability with respect to various types of periodic ordering of the two kinds of ions is found.