2007 Volume 15 Pages 67-71
We have developed a unique method for direct numerical simulations (DNS) of dense colloidal dispersions. This method enables us to compute the time evolutions of colloidal particles, ions, and host fluids simultaneously by solving Newton, advection-diffusion, and Navier-Stokes equations so that the electro-hydrodynamic couplings can be fully taken into account. The electrophoretic mobilities of charged spherical particles are calculated in several situations. The comparisons with approximation theories show quantitative agreements for dilute dispersions without any empirical parameters; however, our simulation predicts notable deviations in the case of dense dispersions. Recently, our DNS code was modified to take into account the effect of Brownian motions of the particles. The new code has been applied to several cases where coupling between hydrodynamic interaction and the thermal fluctuation becomes important. Striking examples include chain formations of likely charged particles due to the application of external electric fields and dynamics of chain conformations fluctuating in host fluids. We also observed clear tendency of the shear thickening behavior when we apply shear flow to dense colloidal dispersions. The origin of the thickening will be studied in future.