Rheology and dynamics of sheared arrays of colloidal particles

Concentrated suspensions of colloidal particles undergo dynamical microstructural transitions under shear. During the transition from oscillating face-centered cubic twin structures to sliding layer structures, the system can exhibit hysteretic and discontinuous rheology as the shear rate is varied. We capture this behavior with a dynamic simulation of a sheared lattice of non-Brownian spherical particles with screened electrostatic interactions and hydrodynamic interactions determined using the Stokesian dynamics approximation. Rheological data are determined for a range of volume fractions, electrostatic screening lengths and shear rates or shear stresses. In controlled stress simulations, static yield stresses are observed. In controlled shear rate simulations of certain lattice orientations, plateau viscosities are observed at high and low shear rates with a high to low shear rate plateau viscosity ratio ranging from 1.4 to 2.2. Large viscosity transitions with hysteretic-like rheology are observed only in controlled shear rate simulations of face-centered cubic (111) layers sheared parallel to the (211) direction with full representation of the hydrodynamic particle interactions. Rheological curves collapse when stresses are scaled by the elastic modulus and shear rates by the elastic modulus divided by the high-shear-rate limiting viscosity. The magnitude of the hysteretic viscosity jump and the scaled critical stresses match experimental values.