1 VISCOSITY OF CONCENTRATED SUSPENSIONS: INFLUENCE OF CLUSTER FORMATION

Dispersed particles can form clusters even at sufficiently low concentrations. Colloidal and hydrodynamic forces are responsible for this phenomenon and these forces determine both structure and size of clusters. We assume that viscosity of concentrated suspension is completely determined by cluster size distribution, no matter if clusters form under the action of colloidal, hydrodynamic interactions or shear rates. Based on this assumption an equation, which describes dependency of viscosity on a concentration of dispersed particles taking into account cluster formation, is deduced. Under special restrictions the deduced dependency coincides with the well-known Douherty-Krieger’s equation except for a clear physical meaning of entering parameters. Our consideration shows that Douherty-Krieger’s equation has deeper physical background than it has been supposed earlier. Experimental verification of the suggested model shows a good agreement with the theory predictions and proves a presence of clusters even at low concentrations of dispersed particles. Key words: cluster size distribution, viscosity, concentrated suspensions. ƒ To whom correspondence should be addresse