Phase behaviour of attractive and repulsive ramp fluids: integral equation and computer simulation studies

TL;DR

This study combines simulations and integral equations to explore phase behaviors of ramp fluids, revealing liquid-liquid and fluid-solid transitions influenced by attractive and repulsive interactions, with complex phase diagram topologies.

Contribution

It provides new insights into phase transitions of ramp fluids using combined computational and theoretical methods, highlighting the effects of attraction and repulsion on phase topology.

Findings

Attractive ramp fluids exhibit liquid-liquid de-mixing and fluid-solid transitions.

Repulsive ramp fluids show similar solidification, preventing fluid-fluid separation.

Complex phase diagram topology arises from the interplay of interactions.

Abstract

Using computer simulations and a thermodynamically self consistent integral equation we investigate the phase behaviour and thermodynamic anomalies of a fluid composed of spherical particles interacting via a two-scale ramp potential (a hard core plus a repulsive and an attractive ramp) and the corresponding purely repulsive model. Both simulation and integral equation results predict a liquid-liquid de-mixing when attractive forces are present, in addition to a gas-liquid transition. Furthermore, a fluid-solid transition emerges in the neighbourhood of the liquid-liquid transition region, leading to a phase diagram with a somewhat complicated topology. This solidification at moderate densities is also present in the repulsive ramp fluid, thus preventing fluid-fluid separation.