Theory for the phase behaviour of a colloidal fluid with competing interactions

TL;DR

This paper develops a theoretical framework to understand the complex phase behavior of colloidal fluids with competing interactions, predicting both uniform and modulated phases and their transition types.

Contribution

It introduces an order parameter theory based on density functional theory to analyze phase transitions, including tricritical points, in colloidal fluids with complex pair potentials.

Findings

Prediction of first and second order phase transitions.

Identification of two tricritical points in the phase diagram.

Detailed analysis of modulated inhomogeneous phases.

Abstract

We study the phase behaviour of a fluid composed of particles which interact via a pair potential that is repulsive for large inter-particle distances, is attractive at intermediate distances and is strongly repulsive at short distances (the particles have a hard core). As well as exhibiting gas-liquid phase separation, this system also exhibits phase transitions from the uniform fluid phases to modulated inhomogeneous fluid phases. Starting from a microscopic density functional theory, we develop an order parameter theory for the phase transition in order to examine in detail the phase behaviour. The amplitude of the density modulations is the order parameter in our theory. The theory predicts that the phase transition from the uniform to the modulated fluid phase can be either first order or second order (continuous). The phase diagram exhibits two tricritical points, joined to one another by the line of second order transitions.