Kadanoff Prize: Granular Physics Meets Suspension Rheology

Concentrated (“dense”) suspensions of fine solid particles in a liquid are ubiquitous in our daily lives as well as industry and also geophysics. Crowding of particles induces multiscale interactions, ranging from local particle-level contact forces to macroscopic, system-spanning contact networks that dynamically evolve under applied shear. The result is a rich set of complex, shear-induced phenomena, including dramatic increases in apparent viscosity and a fully reversible transformation from viscous fluid all the way to brittle solid. Over the last decade and a half, a confluence of ideas from granular physics and rheology has led to a new level of understanding of many of these phenomena, much of it based on the realization that sufficiently strong shear can overcome particle lubrication and activate friction as surfaces come into close proximity. More recently, exploiting not only physical but also chemical contributions to an effective friction has led to new opportunities for designing the response to stress. This talk will discuss some of these results and show how dense suspensions, along the way, have become a model system for studying non-thermal, dynamical state transitions in soft matter physics.