Brownian dynamics simulation of a dispersion composed of disk-like hematite particles regarding the orientational distribution and the magneto-rheological properties

Abstract

We have investigated the orientational distribution and magneto-rheological characteristics of a disk-like hematite particle dispersion by means of Brownian dynamics simulations. The present Brownian dynamics method takes into account the spin Brownian motion about the particle axis in addition to the ordinary translational and rotational Brownian motion. In order to clarify the validity of the present simulation results, they are compared with the corresponding results obtained by a theory based on the orientational distribution function. This comparison clearly shows that the present simulation results are in good agreement with the theoretical results. In the situation of a strong applied magnetic field, the particles can freely rotate about the magnetic moment direction whilst the magnetic moment is aligning in the magnetic field direction. If the shear flow becomes dominant, a single peak-type orientational distribution becomes significant. This is because column-like clusters tend to incline in the direction of the angular velocity vector of a simple shear flow in a strong shear flow situation. The viscosity due to the magnetic properties of the particles significantly increases with increasing magnetic field strength. An increase in the magnetic particle–particle interaction strength leads to a decrease in the viscosity. Unless the regime of aggregation structures changes, the viscosity monotonically decreases with increasing Peclet number.