Ionic fluids: charge and density correlations near gas-liquid criticality

TL;DR

This paper investigates how charge and density correlations in ionic fluids behave near gas-liquid criticality, revealing the conditions under which the Stillinger-Lovett rule holds or breaks down.

Contribution

It provides explicit expressions for correlation functions near criticality and clarifies the validity of the Stillinger-Lovett rule in asymmetric ionic fluids.

Findings

SL rule holds away from critical point

SL rule is violated at critical point in asymmetric models

In symmetric models, SL rule holds even at criticality

Abstract

The correlation functions of an ionic fluid with charge and size asymmetry are studied within the framework of the random phase approximation. The results obtained for the charge-charge correlation function demonstrate that the second-moment Stillinger-Lovett (SL) rule is satisfied away from the gas-liquid critical point (CP) but not, in general, at the CP. However in the special case of a model without size assymetry the SL rules are satisfied even at the CP. The expressions for the density-density and charge-density correlation functions valid far and close to the CP are obtained explicitely.