Relationship between aggregate regime and magneto-rheology of a ferromagnetic rod-like particle suspension by means of Brownian dynamics simulations

In the present study, we focus on a ferromagnetic rod-like particle suspension to discuss the dependence of the magneto-rheological properties on the regime of aggregates of the magnetic rod-like particles. To do so, we here adopted Brownian dynamics simulations in a simple shear flow situation, in order to investigate this dependence in various situations. The main results obtained here are summarized as follows. In a weak applied magnetic field, the particles tend to aggregate to form raft-like clusters if the magnetic particle-particle interaction is sufficiently larger than thermal motion. As the magnetic field is increased, these raft-like clusters change into chain-like clusters and finally grow into wall-like clusters along the magnetic field direction. These wall-like clusters give rise to much larger resistance to the flow field than single-moving particles (and also than chain-like clusters). Moreover, the wall-like and thick chain-like clusters become more resistant than raft-like clusters, which leads to larger values of the net viscosity. From the present results, we conclude that the viscosity due to magnetic properties of rod-like particles exhibits complex dependence on the regime of particle aggregate structures such as raft-like, chain-like and wall-like clusters, which is strongly influenced by the magnetic field strength, the magnetic particle-particle interaction strength and the shear rate.