On the Negative Magneto-Rheological Effect of a Suspension Composed of Rod-Like Hematite Particles by Means of Brownian Dynamics Simulations with Spin Brownian Motion

Abstract

We have investigated the behaviors of rod-like hematite particles in a simple shear flow as well as in an applied magnetic field, in order to clarify the dependence of the negative magneto-rheological effect on particle aggregation and orientational distribution of particles. The present Brownian dynamics method has a significant advantage that it takes into account the spin rotational Brownian motion around the particle axis in addition to the ordinary translational and rotational Brownian motion. The net viscosity is decomposed into three components and discussed at a deeper level and in more detail: these three viscosity components arise from (a) the torque due to the magnetic particle-field interaction and (b) the torque and (c) the force due to the interaction between particles. In contrast to the ferromagnetic rod-like particle that exhibits a single-peak-type orientational distribution, the present hematite particle has a linear-peak-type distribution with a much more gentle profile. Hence, the orientational distribution does not change significantly. However, this slightly reformed distribution makes a significant influence on the negative magneto-rheological effect. In a dilute suspension, the effect of the magnetic field strength on this negative magneto-rheological effect is qualitatively and quantitatively in good agreement with that obtained by the previous theory and Brownian dynamics simulations without translational Brownian motion. In a relatively dense suspension, the viscosity components arising from an applied magnetic field and the interaction between particles come to change rapidly since certain strength of magnetic particle-particle interaction, which is due to the formation of raft-like clusters.