Microstructure of a near-critical colloidal dispersion under stationary shear flow

Microstructural order of near-critical suspensions of colloid-polymer mixtures under stationary shear flow is investigated by means of small-angle light scattering. The experiments reveal a significant, unexpected shear-induced distortion in directions perpendicular to the flow direction, the more so on closer approach to the gas-liquid critical point. Starting from the N-particle Smoluchowski equation, we derive an explicit expression for the shear-rate dependence of the static structure factor. The present theory improves on a previous treatment, by taking the shear-induced distortions of short-ranged correlations into account, which are indeed shown to be important on close approach to the critical point. The experiments are in quantitative accordance with this extended theory, for all wavevectors', shear rates, and distances from the gas-liquid critical point.