Rheological properties of suspensions of spheres in non-Newtonian media

Abstract

The results of an experimental investigation of the rheologioal properties of dilute suspensions of rigid spheres 100μm in diameter in non-Newtonian pseudoplastic liquids are reported. The shear flow properties of suspensions in a solution of polyisobutylene in tetralin, in aqueous solutions of polyacrylamide and sodium carboxymethylcellulose and in a Newtonian fluid have been investigated at solid concentrations up to 10% by volume. A concentric cylinder viscometer was used, results being corrected for end effects and variations in shear rate across the gap. Results for the Newtonian fluid were not inconsistent with published data. It was found that, within the range of variables investigated, for each of the non-Newtonian fluids the relative fluidity, comparing the suspension and the suspending fluid at the same shear stress, was a function of concentration only whereas the relative fluidity comparing the suspension and the fluid at the same shear rate depended on both concentration and shear rate. The fractional decrease in fluidity produced by a given concentration of spheres in polyisobutylene solution was about double that produced by the same concentration in any of the other fluids. In what are believed to be the first reported measurements of normal stress in suspensions, the first normal stress difference (p 11-p 22 for the fluids was derived from the normal force exerted on the cone of a Rheogoniometer during steady rotation. Over ranges of concentration and shear rate limited by experimental difficulties the ratio of shear rate to normal stress for the suspension divided by the corresponding quantity for the base solution appeared to be a function of concentration only when the liquids were compared at the same normal stress but not when compared at the same shear rate. However, this conclusion was less certain than the corresponding result for relative fluidity.