Viscosity and diffusion in hard-sphere-like colloidal suspensions

A large number of experimental data on the viscous and the diffusive behavior at short and long times in three classes of disordered hard-sphere-like colloidal suspensions with varying polydispersity is compared with theory. At low and intermediate concentrations (volume fraction φ<0.35) a hydrodynamic description obtains. An alternative molecular approach, which can be generalized to high concentrations, is also presented. At high concentrations (φ>0.35) the dominant contributions, however, come from direct interactions in cage diffusion, whose rapidly increasing difficulty with increasing concentration, leads to a singularity-dominated increase (decrease) of the viscosity (self- and collective diffusion coefficient).