Monte Carlo simulation of the nonadditive restricted primitive model of ionic fluids: Phase diagram and clustering

TL;DR

This study uses Monte Carlo simulations to explore how non-additive hard-sphere diameters affect the phase diagram and clustering in ionic fluids, revealing that non-additivity influences clustering behavior and phase transition points.

Contribution

It provides the first detailed Monte Carlo analysis of the phase diagram and clustering in non-additive restricted primitive models of ionic fluids, highlighting the effects of non-additivity.

Findings

Negative nonadditivity promotes neutral cluster formation.

Positive nonadditivity enhances like-ion pairing at high density.

Critical points shift with nonadditivity, affecting phase transition conditions.

Abstract

We report an accurate Monte Carlo calculation of the phase diagram and clustering properties of the restricted primitive model with non-additive hard-sphere diameters. At high density the positively non-additive fluid shows more clustering than the additive model and the negatively non-additive fluid shows less clustering than the additive model, at low density the reverse scenario appears. A negative nonadditivity tends to favor the formation of neutrally charged clusters starting from the dipole. A positive nonadditivity favors the pairing of like ions at high density. The critical point of the gas-liquid phase transition moves at higher temperatures and higher densities for a negative nonadditivity and at lower temperatures and lower densities for a positive nonadditivity. The law of corresponding states does not seem to hold strictly. Our results can be used to interpret recent experimental works on room temperature ionic liquids.