The nonlinear rheological properties of dense suspensions are discussed
within simplified models, suggested by a recent first principles approach to
the model of Brownian particles in a constant-velocity-gradient solvent flow.
Shear thinning of colloidal fluids and dynamical yielding of colloidal glasses
arise from a competition between a slowing down of structural relaxation,
because of particle interactions, and enhanced decorrelation of fluctuations,
caused by the shear advection of density fluctuations. A mode coupling approach
is developed to explore the shear-induced suppression of particle caging and
the resulting speed-up of the structural relaxation.Comment: 33 pages, 10 figures; accepted for publication in Faraday Disc. 123
(2002); small numerical correction
