STOKESIAN DYNAMICS SIMULATIONS OF FERROMAGNETIC COLLOIDAL DISPERSIONSIN A SIMPLE SHEAR-FLOW

We have investigated the behavior of clusters of ferromagnetic particl es in a colloidal dispersion subjected to a simple shear flow. To do s o, the Stokesian dynamics method has been used under the assumption th at the effect of Brownian motion is negligible, For the case of no she ar flow, the aggregate structures obtained by the Stokesian dynamics s imulations agree well with Monte Carlo results qualitatively. We can, therefore, conclude that the Stokesian dynamics simulations can captur e thick chainlike clusters without introducing a specific clustering a lgorithm, which is indispensable for Monte Carlo simulations, The beha vior of the thick chainlike clusters in a simple shear flow is summari zed as follows. The thick chainlike clusters decline in the shear how direction as time advances, Since longer clusters experience larger sh ear forces, it is difficult for them to survive in such a situation.Th e thick chainlike clusters, therefore, dissociate into some short clus ters. Such clusters are relatively stable in a shear flow, so that the y do not decrease significantly any more. The viscosities have a stron g relationship with the internal structures of the aggregates. The ins tantaneous viscosities, therefore, fluctuate significantly for the cas e of the thick chainlike clusters, (C) 1998 Academic Press.