SHEAR-FLOW-INDUCED MICROSTRUCTURAL DISTORTION NEAR THE CRITICAL-POINT

Shear-flow-induced microstructural distortion of suspensions close to the critical point is described in detail on the basis of the Smolucho wski equation, where hydrodynamic interaction is neglected. The soluti on of the Smoluchowski equation exhibits scaling behaviour, predicting that the combined shear rate and correlation length dependence is cha racterized by a single dimensionless number lambda similar to gamma xi (4) (With gamma the shear rate and xi the correlation length of the un sheared suspension). From the scaling relations for deformation of the structure factor, a scaling form for the turbidity is derived. Experi ments concerning these phenomena are presented, some of which are prel iminary. Two types of systems are used, bath of which exhibit a gas-li quid critical point: stearyl silica in benzene and stearyl silica in c yclohexane with polydimethylsiloxane. Although there is an overall agr eement with the theory, there remains a discrepancy in some of the qua ntitative comparisons, probably due to the neglect of hydrodynamic int eraction and the approximate nature of the closure relation that is us ed for the three-particle correlation function.