Abstract

Concentrated suspensions of hard particles such as cornstarch in water exhibit shear thickening, a non-Newtonian fluid behavior in which an increasing shear rate causes the effective viscosity of the fluid to increase, and even support a load or crack like a solid.  Such suspensions can even be strong enough to support a person walking or running on the surface of the fluid.  These material properties are promising for applications such as rate-dependent dampers and impact protection. My group carries out experiments to obtain a constitutive relation between stress, strain, and strain rate that can describe the material properties, and to understand how it relates to the properties of the suspended particles and their many-body interactions.  At the microscopic scale, particles can interact through many forces, including contact friction, electrostatic interactions, and even surface tension at the boundary of the suspension.  As these flows consist of many hard particles in contact or near-contact, connections to granular flows abound; dilation plays a major role in the mechanics, and the jamming transition (where the particle concentration is just large enough that they form a system-spanning contact network) acts as a critical point that controls the strength of shear thickening.  The end goal of this research is to understand the materials well enough to design materials customized for different applications.