A large number of experimental data on the viscous and the diffusive b
ehavior at short and long times in three classes of disordered hard-sp
here-like colloidal suspensions with varying polydispersity is compare
d with theory. At low and intermediate concentrations (volume fraction
phi < 0.35) a hydrodynamic description obtains. An alternative molecu
lar approach, which can be generalized to high concentrations, is also
presented. At high concentrations (phi > 0.35) the dominant contribut
ions, 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). (C) 1998 Elsevier Science B.V. All
rights reserved.