Phase behavior of a fluid with competing attractive and repulsive interactions

TL;DR

This study investigates the complex phase behavior of fluids with competing attractive and repulsive interactions, revealing new phase transitions and structures through simulations and theoretical analysis.

Contribution

It provides a combined simulation and theoretical analysis of phase behavior in fluids with competing interactions, identifying new first-order transitions and phase structures.

Findings

Repulsive interactions replace the liquid-vapor critical point with two first-order transitions.

Discovery of a transition between vapor and a cluster fluid, and another between liquid and voids.

Percus-Yevick approximation captures key features of the new phase transitions.

Abstract

Fluids in which the interparticle potential has a hard core, is attractive at moderate separations, and repulsive at greater separations are known to exhibit novel phase behavior, including stable inhomogeneous phases. Here we report a joint simulation and theoretical study of such a fluid, focusing on the relationship between the liquid-vapor transition line and any new phases. The phase diagram is studied as a function of the amplitude of the attraction for a certain fixed amplitude of the long ranged repulsion. We find that the effect of the repulsion is to substitute the liquid-vapor critical point and a portion of the associated liquid-vapor transition line, by two first order transitions. One of these transitions separates the vapor from a fluid of spherical liquidlike clusters; the other separates the liquid from a fluid of spherical voids. At low temperature, the two transition lines intersect one another and a vapor-liquid transition line at a triple point. While most integral equation theories are unable to describe the new phase transitions, the Percus Yevick approximation does succeed in capturing the vapor-cluster transition, as well as aspects of the structure of the cluster fluid, in reasonable agreement with the simulation results.