We have investigated the sedimentation phenomena of colloidal dispersions composed of spherical ferromagnetic particles using Brownian dynamics simulations. We have attempted to clarify the conditions causing all particles to subside and high surface density thin films to form under strong magnetic field conditions by varying the applied magnetic field, magnetic force between particles, mass density, and solution temperature. The main results obtained are summarized as follows. As the mass density of the particles increases and magnetic force between particles decreases, cluster formation is difficult and, therefore, thin films are more likely to form. In addition, cluster formation is difficult because a strong magnetic field constrains the magnetic moment of a particle in the direction of the magnetic field, allowing a thin film to be formed. A limitation exists, however, where the thin film formation condition does not increase when the magnetic field exceeds a certain level. Furthermore, when the temperature of the liquid is low and the magnetic force between particles has an intermediate value, a unique cluster formed by two particles oriented in the magnetic field direction appears. However, as the temperature of the liquid increases, the cluster collapses because of the Brownian force, causing the desired thin film to be formed.
2017 Japan Society for Simulation Technology