Shear Thickening in Concentrated Suspensions
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 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 that concentrated suspensions share many mechanical features of granular materials. I will also discuss other connections with the mechanics of particulate fluids, and new considerations that need to be made in models of concentrated particulate fluids.
Eric Brown received a B.S. in Physics from Harvey Mudd College (2002), and a Ph.D. in Physics from the University of California at Santa Barbara (2007) for his work on heat transport and the dynamics of large-scale flows in turbulent Rayleigh-Benard convection. He is currently a postdoctoral scholar in the James Franck Institute at The University of Chicago working with Dr. Heinrich Jaeger. His current research interests include rheology of complex fluids, mechanics of granular materials, and turbulent flows.