Three-dimensional Monte Carlo Simulations of Internal Aggregate Structures in a Colloidal Dispersion Composed of Rod-like Particles with Magnetic Moment Normal to the Particle Axis

Abstract

We have investigated aggregation phenomena of a colloidal dispersion composed of ferromagnetic rod-like particles with a magnetic moment normal to the particle axis, by means of three-dimensional cluster-moving Monte Carlo simulations. Concretely, we have treated a monodispersed model system in order to clarify the influences of the volumetric fraction of particles, magnetic interactions between particles, etc., on particle aggregation phenomena. Aggregate structures have been discussed qualitatively in terms of radial distribution, orientational pair correlation functions, etc. The main results obtained here are summarized as follows. Rod-like particles tend to aggregate to form raft-like clusters along the magnetic moment direction as magnetic particle-particle interactions increase. In such raft-like clusters, the direction of each particle axis has a tendency to align in parallel formation, but is not significantly parallel as expected. As the volumetric fraction increases, longer raft-like clusters are formed. However, such raft-like clusters do not aggregate further to form thicker clusters, which is in significantly contrast with dispersions of spherical or rod-like particles with a magnetic moment along the particle axis, where thicker chain-like clusters are observed under certain conditions.