THE RHEOLOGY OF A CONCENTRATED COLLOIDAL SUSPENSION OF HARD-SPHERES

The rheology of a model hard-sphere suspension has been studied at high volume fraction. Particular emphasis was placed on observing the transition between liquid-like and solid-like behavior at the maximum packing volume fraction. Capillary viscometry has shown that the suspension viscosity at low concentration agrees well with theory and other experimental work on hard-sphere systems. At higher concentrations the rheological properties, measured using steady shear, oscillatory shear, and creep techniques, change rapidly from viscous Newtonian to shear-thinning viscoelastic. When the volume fraction is greater than the maximum packing volume fraction the behavior is like that of an elastic solid, and a yield stress can be measured using cone and plate instruments and the vane method. At high volume fractions the product of a characteristic shear rate (or Peclet number) and the low shear limiting viscosity is found to be almost independent of concentration. It is possible to superimpose all the steady shear data using a scaling based on the Cross equation. © 1991.