Numerical analysis of the aggregate structure of ferrofluid under the uniform magnetic fields (Study on the mesoscopic system)

Ferrofluid has the property that responds to the change in the magnetic field. The aggregate structure of magnetic particles has an effect on the rheological properties. For example, the effective shear viscosity increases with the intensity of magnetic field. We are studying the aggregate structure of ferrofluids by the Stokesian dynamics simulation except for Brownian motions. In this paper, we discuss the aggregate structure of ferrofluids from the viewpoint of mesoscopic system that consists of some calculation cells, for the purpose of understanding the whole aggregation state. Results obtained are as follows. (1) The aggregation of magnetic particles is parallel to the direction of magnetic field. (2) The aggregation diameter increases with reduction of the magnetic moment. The aggregation is thin at a small magnetic moment. (3) The aggregation of magnetic particles forms the uniform hexagonal structure on the plane perpendicular to the direction of magnetic field at a large intensity of magnetic field and magnetic moment.