Flow Behavior of Concentrated Suspensions

Abstract

Concentrated suspensions of noninteracting particles show dilatancy at high shear rates, whereas flocculated suspensions are generally pseudoplastic over a wide range of shear rates. The effects of colloidal attraction between particles on the dilatant flow are examined for aqueous suspensions of zinc sulfide (ZnS). The particle-particle interactions are controlled by surface treatment of particles and addition of surfactant. The steady-flow properties were measured for suspensions at concentrations from 40 to 55% by volume and the degree of colloidal stability was evaluated by the particle concentration in the sediment. With decreasing particle concentration in the sediment, i.e., with increasing colloidal interactions, the dilatant behavior becomes less obvious. For the appearance of dilatant flow, the flocs must be broken down to primary particles in shear fields. The hydrodynamic forces required to break the flocs were calculated.