Development of effective stokesian dynamics method for ferromagnetic colloidal dispersions (cluster-based stokesian dynamics method)

We have developed a new Stokesian dynamics (SD) method for non-dilute colloidal dispersions, which enables us to reduce drastically the computation time. To verify the validity of the present method, which is called the cluster-based SD method, the simulations of a ferromagnetic colloidal dispersion have been carried out for a simple shear flow. The correlation function and the viscosity have been evaluated in order to compare the results obtained by the present method with those obtained by the ordinary SD method and the method of ignoring hydrodynamic interactions between particles. The results obtained here are summarized as follows. The transient properties from an initial state obtained by the present method agree well with those by the ordinary method, even if the radius γclstr, which defines the cluster formation, is taken as a small value such as γclstr=1.2d (d is the particle diameter). Also, concerning the equilibrium properties such as the pair correlation function and the viscosity, the present cluster-based method gives a satisfactory agreement with the ordinary SD method. Furthermore, the cluster-based method drastically reduces the computation time by about one fourteenth to one seventieth compared with the ordinary method. It is clear from these results that the cluster-based SD method is significantly superior to the ordinary SD method for ferromagnetic colloidal dispersions for which a large model system such as = 1 000 or 10 000 is indispensable in simulations.