A dynamic jamming point for shear thickening suspensions

Densely packed suspensions can shear thicken, in which the viscosity increases with shear rate. We performed rheometry measurements on two model systems: corn starch in water and glass spheres in oils. In both systems we observed shear thickening up to a critical packing fraction $\phi_c$ ($=0.55$ for spherical grains) above which the flow abruptly transitions to shear thinning. The viscosity and yield stress diverge as power laws at $\phi_c$. Extrapolating the dynamic ranges of shear rate and stress in the shear thickening regime up to $\phi_c$ suggests a finite change in shear stress with zero change in shear rate. This is a dynamic analog to the jamming point with a yield stress at zero shear rate.