Pattern formation in binary colloids

Abstract

An experimental and theoretical study of the formation of structures in a binary monolayer of dipolar particles is presented. We construct an experimental technique for an easy to control realization of a binary monolayer where the two components have oppositely oriented dipole moments constrained perpendicular to the plane of motion. The experimental set-up ensures that hydrodynamic effects do not play a crucial role in the structure formation, the particles move deterministically due to the dipole–dipole interaction. At low concentrations cluster–cluster aggregation occurs with chain-like morphologies, while at high concentration the particles self-assemble into various types of binary crystal lattices. We propose a simple theoretical framework to describe the observed structure formation. Based on molecular dynamics simulations and analytic calculations we show that the total concentration of the particles, the relative concentration and the relative dipole moment of the components determine the structure of the dipolar monolayer. The theoretical results are in satisfactory agreement with the experimental findings.