THE VISCOSITY OF SEMIDILUTE, BIDISPERSE SUSPENSIONS OF HARD-SPHERES

The viscosity of semidilute bimodal suspensions of sterically stabiliz ed silica particles was measured as a function of the total volume fra ction and the size ratio of the dispersed particles, and of the compos ition of the mixtures. The unimodal components of which the bimodal su spensions were composed showed hard sphere behavior. In the mixtures, a minimum in the viscosity was observed at small size ratios (a(l)/a(s )<2) when plotted against the composition. For larger size ratios a ma ximum was found. The origin of the viscosity maximum is uncertain but might be explained by depletion forces.