Condensed Matter Seminar Series

Shear Thickening in Concentrated Suspensions

Eric Brown

University of Chicago

Thursday April 14,  11:00 am,  Room 298,  Physics Building

Abstract:  Particulate fluids such as colloids, suspensions, foams, emulsions, and granular materials can exhibit a variety of mechanical properties.  One of the most dramatic of these properties is shear thickening in concentrated suspensions and colloids, in which the effective viscosity reversibly and discontinuously jumps by orders-of-magnitude as the shear rate is increased.   This phenomenon has not been explained based on traditional hydrodynamic rheology models.  Using rheometry and video microscopy measurements on suspensions, I will show this shear thickening is a response to expansion (dilatancy) of the particle packing under shear, a common feature of granular materials. The expansion strains the boundaries of the system, which respond with a confining stress, for example from the stiffness of the walls or surface tension.  The confining stress is transmitted through the packing along frictional contacts, causing the dramatically enhanced dissipation under shear which is observed as shear thickening.  I will also discuss connections with the mechanics of other particulate fluids, and the consequences for models of concentrated particulate fluids.