LIGHT-SCATTERING-STUDIES OF DISPERSIONS UNDER SHEAR

The use of light scattering to study the structure of colloidal disper sions under shear is described. An apparatus has been constructed whic h can collect two-dimensional scattering data from a range of sample e nvironments, including sheared samples. Shear cells, made of fused qua rtz, of both the disc/disc and Couette type can be used to collect sca ttering data from all three principal axes of a flowing dispersion. Th e shear cells can be driven continuously or in oscillatory motion. Res ults of scattering experiments on sterically stabilised polymethyl met hacrylate latices in organic media will be described. These systems ca n be adjusted so that the refractive index difference between the part icles and the dispersion medium is small (less than 0.01). This permit s measurements on concentrated systems up to 50% volume fraction. Data showing the onset and extent of ordering under shear are presented. T hese results are discussed in terms of models of 'hard-sphere' fluids.