Shear flow of non-Brownian rod-sphere mixtures near jamming

Abstract: We use the discrete element method, taking particle contact and hydrodynamic lubrication into account, to unveil the shear rheology of suspensions of frictionless non-Brownian rods in the dense packing fraction regime. We find that, analogously to the random close packing volume fraction, the shear-driven jamming point of this system varies in a non-monotonic fashion as a function of the rod aspect ratio. The latter strongly influences how the addition of rod-like particles affects the rheological response of a suspension of frictionless non-Brownian spheres to an external shear flow. At fixed values of the total (rods plus spheres) packing fraction, the viscosity of the suspension is reduced by the addition of "short" ( $\leq 2$) rods but is instead increased by the addition of "long" ( $\geq2$) rods. A mechanistic interpretation is provided in terms of packing and excluded-volume arguments.