DISORDER AND ORDER IN SHEARED COLLOIDAL SUSPENSIONS

We study colloidal suspensions in a linearly sheared solvent using sta ndard stochastic field equations, namely, a modified Navier-Stokes equ ation for the solvent's velocity, coupled with the continuity equation for the suspensions' number density. Unlike earlier approaches, activ e mixing is included, leading to distortions in the structure factor f or wave vectors perpendicular to the flow direction. Depending on the nature of the colloidal interactions, the density of the suspension, a nd the magnitude of the shear, spatial correlations can be either enha nced or reduced. Moreover, in strongly interacting systems, a spinodal line can be found, above which the system is unstable to the formatio n of layers perpendicular to the shear gradient. We discuss how our th eory may be used to understand shear thinning or shear thickening, and the transition to lamellar phase seen in simulations.