Brownian dynamics of colloidal-aggregate rotation and dissociation in shear flow

To simulate a system of spherical colloidal particles in shear flow, a Brownian-dynamics scheme has been developed which includes the perturbing effect of the shear field on the hydrodynamic interactions between the particles. Flocculated doublets of DLVO-type particles have been simulated in simple shear, and aggregate lifetimes have been determined as a function of shear rate, secondary-minimum well depth and doublet orientation with respect to the flow. Trajectory analysis shows that a pair may dissociate temporarily by Brownian motion only to be brought together again by the action of the field. It is found that particles with secondary-minimum well depths of several kT may rotate many revolutions before dissociating. With simulated flocs of four non-Brownian DLVO-type particles, the critical shear rate for disruption is found to be linear in the well depth.