Abstract
We have investigated the sedimentation phenomena of a colloidal dispersion composed of spherical ferromagnetic particles using Brownian dynamics simulations. We have attempted to clarify the conditions under which all particles subside and the thin film is formed, by varying the applied magnetic field, magnetic force between particles, mass density, and temperature of solution. The main results obtained are summarized as follows. As the mass density of the particles increases, the influence of gravity increases; hence, sedimentation velocity increases, which makes thin film formation easier. For strong magnetic force between particles, thin film formation is difficult, since the particles combined with each other to form clusters. However, if the applied magnetic field is strong and the magnetic moments of the particles are oriented in the direction of the magnetic field, the clusters disappear and thin film formation occurs, although the same magnetic force exists between the particles. Furthermore, the random force by Brownian motion is required for the cluster collapse and lead to thin film formation. However, if the influence of the random force is too large, the particles on the thin film will be unstable and there is a case where the particle moves upward.
