BROWNIAN DYNAMICS SIMULATIONS OF SEDIMENTATION PHENOMENA OF FERROMAGNETIC SPHERICAL PARTICLES IN A COLLOIDAL DISPERSION

摘要

We have investigated sedimentation phenomena of a colloidal dispersion composed of ferromagnetic spherical particles in the gravity field, by means of Brownian dynamics simulations. In concrete, we have attempted to clarify the influences of the magnetic field strength, magnetic interactions between particles and volumetric fraction of particles on sedimentation phenomena of such magnetic particles. In order to discuss quantitatively the sedimentation process and the internal structures of particle aggregates after the sedimentation, we have concentrated our attention on the local radial distribution function of each layer. The main results obtained here are summarized as follows. For the case of a weak magnetic field and a weak magnetic force between particles, layered structures are formed. As the magnetic field increases, clusters are formed in upright formation along the gravity or the magnetic field direction. As magnetic particle-particle interactions increase, particles combine with each other to form aggregate in other directions, and new types of clusters are formed in the bottom area. In this situation, therefore, the upright-standing clusters come to disappear. For a dilute case, relatively small clusters are formed apart from each other in almost equal space. As the volumetric fraction increases from such a situation, clusters with voids in the center area of the clusters come to be observed, but such formation disappears and layered structures are formed with further increasing the volumetric fraction.