STRUCTURE OF A BINARY COLLOIDAL SUSPENSION UNDER SHEAR

Neutron scattering intensities from an aqueous mixture suspension of 91 nm polystyrene latex particles and 54 nm silica particles are reported in the range 0.02 < Q/nm-1 < 0.2, where Q is the momentum transfer. The suspension was dense at a mixture volume fraction of 0.15, and the polystyrene/silica particle ratio was ca.1.7:1. Results are given for the suspension at rest and under shear. The sheared data were obtained with a concentric cylinder shearing apparatus constructed and tested at the SANS facility of the National Institute of Standards and Technology and the pulsed neutron facility, LANSCE, of the Los Alamos National Laboratory. The design and operation of the cell is described. The shear-influenced behaviour of the mixture is compared with and contrasted to that of a pure polystyrene suspension that can form a crystal lattice in equilibrium, but which melts to a liquid-like structure under shear. A method is proposed to measure, by contrast matching or variation, the polystyrene and silica partial scattered intensities from the mixture suspension in H2O-D2O solvents of different scattering-length densities. Estimates of the partial structure factors are given.