Stress components and shear thickening of concentrated hard sphere suspensions

The elastic-like and viscous-like viscosity components of model, Brownian h ard sphere suspensions were determined. The elastic-like component, sometim es called the thermodynamic component, is due to Brownian motion while the viscous-like component, sometimes called the hydrodynamic component, is due to hydrodynamic interaction between and drag on the particles. The three v olume fractions tested were found to be above the glass transition volume f raction due to the absence of a zero shear viscosity. The hydrodynamic visc osity component was approximately independent of shear rate, yet the suspen sion demonstrated a large amount of shear thinning which was due to the ela stic like component. The measured stress components associated with shear t hickening were distinctly different in each sample. Continuous shear thicke ning was measured for the sample with 0.54 volume fraction while the sample s with volume fractions 0.59 and 0.63 showed discontinuous shear thickening . Shear thickening in these concentrated suspensions was related to the eff ect of particle clustering increasing the effective volume fraction above m aximum packing fraction. The type of shear thickening changed from being vi scous-like for the two lower volume fractions, indicating the formation of particle clusters, to elastic-like for the highest volume fraction. Stress decay after cessation of shear was found to follow a power law relation wit h time indicative of fractal-like microstructures.