A Connection Between Shear Thickening and Jamming
A Connection Between Shear Thickening and Jamming
Friday, August 21, 2009
In Newtonian fluids the viscosity does not change with an applied shear rate, while non-Newtonian fluids usually show a decrease of viscosity when sheared faster; i.e., they shear thin. The opposite behavior, shear thickening, is less common but can be quite dramatic: beyond a certain shear rate the viscosity increases potentially by orders of magnitude. We used rheometry measurements to characterize the critical behavior in two model shear thickening suspensions: cornstarch in water and glass spheres in oil. The slope of the shear thickening part of the viscosity curve is found to increase dramatically with packing fraction and diverge at a critical packing fraction. The magnitude of the viscosity and the yield stress are also found to have scalings that diverge at that same critical packing fraction. We observe shear thickening as long as the yield stress is less than the stress at the viscosity maximum. Above this point the suspensions transition to purely shear thinning. Based on these data we developed a dynamic jamming phase diagram for suspensions and show that a limiting case of shear thickening corresponds to a jammed state.
•Eric Brown and Heinrich M. Jaeger, "Dynamic Jamming Point for Shear Thickening Suspensions ", Phys. Rev. Lett. 103, 086001 (2009). pdf