The motion of colloidal clusters made of spherical particles in the presence of complex flow fields has not been thoroughly investigated thus far. Nevertheless, processing of colloidal dispersions under the conditions where coagulation is induced, leading to formation of complex fractal clusters, and their aggregation kinetics is strongly influenced by their interactions with the flow field. In order to better understand the nature of these interactions, we have used Stokesian Dynamics simulations to derive rigid body equations for clusters of spherical particles under both sheared and non-sheared flow conditions. To estimate the rigid body resistance matrix the grand resistance matrix obtained from the Stokesian dynamics approximation, including many-body interactions and lubrication forces, is used. The dependence of the aggregate motion related coefficients on cluster structure, defined by the fractal geometry and number of primary particles are established and scaling laws are derived.

The derived equations are first used to study the motion of aggregate under gravity. It was found that aggregates always tend to align themselves in the orientation with the least drag. The developed model is further utilized to simulate the motion of aggregates under sheared conditions.

Keywords:

Aggregates, rigid body, Stokesian dynamics