Light scattering measurements of a hard-sphere suspension under shear.

The device described measures a two-dimensional projection of the light scattered from a sheared, optically clear colloidal suspension and decomposes the pattern to identify quantitatively the effects of shear on the structure of the dispersion. The evolution of the nonequilibrium structure for a hard-sphere suspension is traced from low to high shear rates at moderate to dense concentrations and is related qualitatively to rheological properties. At high shear rates shear induces order in dense suspensions. Comparison of the measured nonequilibrium structure factor at low shear rates to theoretical predictions based on pairwise additive interactions confirms the importance of many-body hydrodynamics, as suggested by similar discrepancies between measurements of the steady shear viscosity and predictions from the same theory. Scalings that correlate the shear rate dependence of the viscosity appear to work for the microstructure as well. Measurements of a similar suspension with weak long-range repulsions demonstrates the sensitivity of the nonequilibrium microstructure to the form of the interparticle potential. [ABSTRACT FROM AUTHOR]