Stokesian Dynamics Simulations of Ferromagnetic Colloidal Dispersions in a Simple Shear Flow.

We have investigated the behavior of clusters of ferromagnetic particles in a colloidal dispersion subjected to a simple shear flow. To do so, the Stokesian dynamics method has been used under the assumption that the effect of Brownian motion is negligible. For the case of no shear flow, the aggregate structures obtained by the Stokesian dynamics simulations agree well with Monte Carlo results qualitatively. We can, therefore, conclude that the Stokesian dynamics simulations can capture thick chainlike clusters without introducing a specific clustering algorithm, which is indispensable for Monte Carlo simulations. The behavior of the thick chainlike clusters in a simple shear flow is summarized as follows. The thick chainlike clusters decline in the shear flow direction as time advances. Since longer clusters experience larger shear forces, it is difficult for them to survive in such a situation. The thick chainlike clusters, therefore, dissociate into some short clusters. Such clusters are relatively stable in a shear flow, so that they do not decrease significantly any more. The viscosities have a strong relationship with the internal structures of the aggregates. The instantaneous viscosities, therefore, fluctuate significantly for the case of the thick chainlike clusters. Copyright 1998 Academic Press.