Simulation of a two-dimensional model for colloids in a uniaxial electric field

TL;DR

This study uses Monte Carlo simulations to model colloidal particles under an electric field, revealing cluster formation, percolation, and pressure anomalies without void phases, enhancing understanding of colloidal behavior in external fields.

Contribution

It introduces a simplified 2D model for colloids in an electric field, capturing chain formation, effective interactions, and phase behaviors not previously detailed.

Findings

Formation of cluster phases at low temperature and density

Percolation associated with pressure anomalies

Absence of void phases at low densities

Abstract

We perform Monte Carlo simulations of a simplified two-dimensional model for colloidal hard spheres in an external uniaxial AC electric field. Experimentally, the external field induces dipole moments in the colloidal particles, which in turn form chains. We therefore approximate the system as composed of well formed chains of dipolar hard spheres of a uniform length. The dipolar interaction between colloidal spheres gives rise to an effective interaction between the chains, which we treat as disks in a plane, that includes a short range attraction and long range repulsion. Hence, the system favors finite clustering over bulk phase separation and indeed we observe at low temperature and density that the system does form a cluster phase. As density increases, percolation is accompanied by a pressure anomaly. The percolated phase, despite being composed of connected, locally crystalline domains, does not bear the typical signatures of a hexatic phase. At very low densities, we find no indication of a "void phase" with a cellular structure seen recently in experiments.