The non-Newtonian rheology of hydrodynamically interacting colloids via active, nonlinear microrheology

Abstract

The non-Newtonian rheology of a dilute suspension of hydrodynamically interacting colloids is studied theoretically via active, nonlinear microrheology. In this Stokes-flow regime, a Brownian probe is driven through the suspension by a fixed external force; its motion distorts the configuration of background bath particles, which in turn alters probe motion. This interplay was utilized in our recent article to obtain the normal elements of the suspension stress via the nonequilibrium statistical mechanics theory [Chu and Zia, J. Rheol. 60(4), 755–781 (2016)]. In the present article, we focus on the normal stress differences N1 and N2, osmotic pressure Π, and their evolution with the strength of the probe force and strength of hydrodynamic interactions. As hydrodynamic interactions grow from weak to strong, the influence of couplings between the stress and the entrained motion on N1 changes with the strength of flow. When flow is strong, hydrodynamic interactions suppress the magnitude of N1, owing to coll...