Light scattering studies of dispersions under shear

The use of light scattering to study the structure of colloidal dispersions under shear is described. An apparatus has been constructed which can collect two-dimensional scattering data from a range of sample environments, including sheared samples. Shear cells, made of fused quartz, of both the disc/disc and Couette type can be used to collect scattering data from all three principal axes of a flowing dispersion. The shear cells can be driven continuously or in oscillatory motion. Results of scattering experiments on sterically stabilised polymethyl methacrylate latices in organic media will be described. These systems can be adjusted so that the refractive index difference between the particles and the dispersion medium is small (less than 0.01). This permits measurements on concentrated systems up to 50% volume fraction. Data showing the onset and extent of ordering under shear are presented. These results are discussed in terms of models of ‘hard-sphere’ fluids.