Exploration of the volume fraction above which suspensions of spherical and weakly anisotropic colloid particles cannot flow

Abstract

In article II of this series, we describe experiments with dense suspensions of spherical and dumbbell shaped colloid particles (particle diameter ∼1.2 μm). The suspensions are sheared with dynamic and continuous stress. Dynamic stress sweeps are used to characterize a dynamic glass transition volume fraction (φg) and a dynamic yield stress (τy*). Both phenomena are understood in terms of activated naive mode coupling theory. The dynamic yield stress increases with volume fraction and scales with a reduced volume fraction φ* as τy* ∼ φ*4. Under continuous stress, suspensions discontinuously shear thicken at a critical stress (τt*), which is independent of particle shape and particle interaction. The volume fraction at the onset of thickening (φt) is higher for dumbbell particles compared to spheres. Our results suggest that there is a volume fraction where τy = τt, and this volume fraction occurs close to that of random close packing. For larger volume fractions, steady flow is only established through di...