(227w) Concentrated Mixtures of Colloidal and Non-Brownian Spheres

We study the steady shear flow behavior of concentrated suspensions consisting of mixtures of colloidal and non-Brownian spheres.  At a volume fraction of 0.40, the pure colloidal dispersion and pure non-Brownian suspension each exhibit shear thickening behavior, although the onset stress for shear thickening is three orders of magnitude larger for the colloidal dispersion.  These measurements provided insight into how the microstructure is affected by the addition of non-Brownian particles to the colloidal dispersion or vice versa. Furthermore, we propose methods by which to rescale the flow curves such that superposition is achieved.  These findings are of practical significance as many industrial processes involve suspensions consisting of both colloidal and non-Brownian particles.  Most interestingly perhaps is the mitigation and almost complete elimination of shear thickening that occurs with the addition of small amounts of colloidal particles to the concentrated non-Brownian suspension.  This phenomenon may be associated with a reduction in the stress due to frictional contacts between non-Brownian particles.