Elucidation of the relationship between aggregate structures and magnetorheological properties of a magnetic cubic particle suspension by means of Brownian dynamics simulations

Abstract

We have developed a Brownian dynamics simulation technique for a cubic magnetic particle suspension in a simple shear flow in order to elucidate the relationship between the particle aggregates and the magnetorheological characteristics. A magnetic field is applied in the direction normal to the shearing plane. In a weak applied magnetic field, if the magnetic particle–particle interaction strength is sufficiently large, the particles aggregate to form closely-packed clusters even when subject to the influence of the shear flow. As the magnetic field strength is increased, the closely-packed aggregate structures are transformed into chain-like structures. The net viscosity is increased because the chain-like clusters give rise to a larger resistance to the flow field. As the magnetic field strength is further increased, the chain-like clusters grow into wall-like clusters aligned in the direction of the magnetic field. If the wall-like clusters are the predominant clusters, a magnetic force arises due to a characteristic of the particle arrangement in the wall-like clusters that tends to accelerate the flow field and, as a consequence, decrease the net viscosity. From these results, it may be suggested that under certain conditions a magnetic cubic particle suspension may exhibit a negative contribution to the magnetorheological characteristic. Highlights of the present study We have developed a Brownian dynamics (BD) simulation technique for a magnetic cubic particle suspension. BD simulations have been performed in order to investigate the relationship between particle aggregates and magnetorheological properties. The net viscosity exhibits a complex dependence on the regime of particle aggregates. It is suggested that under certain conditions a magnetic cubic particle suspension may exhibit a negative contribution to the magnetorheological characteristics. An increase in the shear rate causes instability in the face-to-face configuration and leads to the collapse of closely-packed clusters.