  The non-Newtonian behavior of a monodisperse concentrated dispersion of
spherical particles was investigated using a direct numerical simulation
method, that takes into account hydrodynamic interactions and thermal
fluctuations accurately. Simulations were performed under steady shear flow
with periodic boundary conditions in the three directions. The apparent shear
viscosity of the dispersions was calculated at volume fractions ranging from
0.31 to 0.56. Shear-thinning behavior was clearly observed at high volume
fractions. The low- and high-limiting viscosities were then estimated from the
apparent viscosity by fitting these data into a semi-empirical formula.
Furthermore, the short-time motions were examined for Brownian particles
fluctuating in concentrated dispersions, for which the fluid inertia plays an
important role. The mean square displacement was monitored in the vorticity
direction at several different Peclet numbers and volume fractions so that the
particle diffusion coefficient is determined from the long-time behavior of the
mean square displacement. Finally, the relationship between the non-Newtonian
viscosity of the dispersions and the structural relaxation of the dispersed
Brownian particles is examined.
