Rheology of non-Brownian particles suspended in concentrated colloidal dispersions at low particle Reynolds number

The shear flow of non-Brownian glass spheres suspended in a concentrated colloidal dispersion that exhibits non-Newtonian rheology is investigated. At low volume fractions, the addition of non-Brownian spherical particles to the colloidal dispersion leads to an increase in the shear viscosity as well as the dynamic moduli. The flow curves of these suspensions are qualitatively similar to the suspending colloidal dispersion medium, and as such, in this semidilute regime, the suspension data can be shifted on to that of the colloidal dispersion medium at constant shear stress with shift factors comparable to those for spherical particles in a Newtonian fluid. At higher volume fractions of non-Brownian spheres, the flow curves change qualitatively and the shear thickening power law exponent becomes an increasing function of particle volume fraction. This increase in the shear thickening power law exponent is shown to be consistent with the effects of confinement on the shear thickening colloidal dispersion and arises from the packing of the larger, non-Brownian particles.