EFFECT OF SHEAR-FLOW ON THE TURBIDITY OF A CRITICAL COLLOIDAL DISPERSION

Experiments concerning the effect of shear flow on the turbidity of a colloidal dispersion close to its gas-liquid critical point are described. Theory predicts that in the mean-field region, the turbidity of the sheared syst em relative to that of the quiescent dispersion is a function of a single dimensionless group lambda that is proportional to gamma xi(-4) (gamma is the shear rate and xi(-1) is the correlation length of the quiescent dispersion at the given temperature). Experiments are found to be in accordance with this scaling behavior. Moreover, the experiments confirm the theoretically predicted lambda dependence. As a model colloidal system, we used spherical silica particles coated with stearyl alcohol. When dissolved in benzene, these colloidal particles attract each other, due to the fact that benzene is a marginal solvent for the stearyl coating. These attractions give rise to a gas-liquid critical point.