Brownian Dynamics Simulations for Investigating Aggregate Structures in a Suspension Composed of Rod-Like Hematite Particles

Abstract

We have investigated aggregation phenomena in a suspension composed of rod-like hematite particles, which have a magnetic moment normal to the particle axis direction, by means of Brownian dynamics simulations. The present Brownian dynamics method takes into account the spin rotational Brownian motion around the particle axis in addition to the ordinary translational and rotational Brownian motion. First, the validity of the present simulation method has been clarified by comparing with results obtained by the fully-established Monte Carlo method. Then, from performing the simulations, we have investigated the influences of magnetic particle-field and particle-particle interactions, shear rate and volumetric fraction of particles on particle aggregation phenomena. Snapshots of aggregate structures are used for qualitative discussion and cluster size distribution, radial distribution function and orientational correlation functions of the direction of particle axis and magnetic moment are focused on for quantitative discussion. The main results obtained here are summarized as follows. The raft-like clusters are significantly formed at a magnetic particle-particle interaction much larger than that for a magnetic spherical particle suspension. This is because the rotational Brownian motion has a significant influence on the formation of clusters for a suspension composed of rod-like particles with large aspect ratio. An applied magnetic field enhances the formation of raft-like clusters. A shear flow does not have a significant influence on the internal structures of clusters, but influences the cluster size distribution of raft-like clusters. The volumetric fraction of particles has a significant effect on the growth of raft-like clusters and clear cluster formation appears from a volumetric fraction between 0.01 and 0.05 in the present simulation circumstances.