Unsteady shear flows of colloidal hard-sphere suspensions by dynamic simulation

Abstract

The rheology during the start-up and cessation of simple shear flow has been investigated for near hard-sphere colloidal suspensions. Simulations augmented by theoretical analysis are used to determine how the non-Newtonian stress development and relaxation depend on the microstructure. Accelerated Stokesian dynamics (ASD) and Brownian dynamics (BD) simulations are used for 0.05 ≤ Pe ≤ 500 in concentrated freely flowing suspensions; the Peclet number defining the ratio of shear to thermal motion is P e = 3 π η γ a 3 / k T with η the suspending fluid viscosity, γ the shear rate, and kT the thermal energy. Theoretical predictions based on the Smoluchowski equation for dilute suspensions are made, and these are primarily used for comparison with results from BD simulations in which hydrodynamic interactions are neglected. For suspensions with hydrodynamics, simulations by ASD are used to probe start-up and flow cessation over a large range of Pe; these studies focus on solid volume fraction ϕ = 0.4, with...