Interview for Faculty Position

Shear thickening in concentrated suspensions and a general stress equation for particulate fluids

Eric Brown

University of Chicago

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 rheology models that include viscous, inertial, and Brownian effects. Using rheometry and video microscopy measurements on suspensions, I will show this shear thickening is caused by expansion of the particle structures against a confining boundary during shear. The boundary responds with a restoring stress which is transmitted through the structure along frictional contacts which cause additional dissipation. These results suggest a more general approach to the rheology of particulate fluids with a stress equation that now includes such confinement effects and other particle interactions. With this new equation I will explain how differences in the rheology of different types of particulate fluids depend on particle parameters.