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 system relative to that of the quiescent dispersion is a function of a single dimensionless group λ that is proportional to γ̇${\xi }^{\mathrm{-}4}$ (γ̇ is the shear rate and ${\xi }^{\mathrm{-}1}$ 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 λ 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.