THE EFFECT OF SHEAR-FLOW ON CRITICAL CORRELATIONS IN COLLOIDAL SYSTEMS - MICROSTRUCTURE, TURBIDITY, AND DICHROISM

On the basis of the Smoluchowski equation, ''the Liouville equation fo r colloidal systems,'' shear flow distortion effects on the structure factor for temperatures and densities close to the spinodal, c.q. the critical point, are considered. The results are valid in the classical region where the equilibrium structure factor attains the Omstein-Zer nike form. From the structure factor distortion we derive scaling rela tions for the shear-rate dependent turbidity and flow dichroism for va rious flow geometries. The dimensionless group which expresses the eff ect of the shear flow is essentially lambda=Pe(0)(gamma)/(xi R(V))(4), with Pe(0)(gamma)=gamma R(v)(2)/2D(0) (gamma is the shear rate, R(v) the range of the pair-interaction potential, xi(-1) the correlation le ngth, D-0 is the Stokes-Einstein diffusion coefficient). As a conseque nce, very small shear rates (small values of Pe(0)) have very large ef fects close to the spinodal, c.q. the critical point, since then xi R( v) is a small number. mow dichroism can be many decades larger than fo r systems far into the stable region of the phase diagram. Relaxation of turbidity and flow dichroism as a shear flow is turned off is also considered. The temperature, density, shear rate, and time dependence of the relaxation is described by scaling functions depending on the t wo dimensionless groups lambda and gamma t (t is the time lapse after switching off the shear flow).