(170b) Restructuring of Colloidal Aggregates in Simple Shear

Authors: 
Harshe, Y. M., ETH Zurich
Morbidelli, M., Institute of Chemical and Bioengineering, ETH Zurich


Abstract:

The industrial processing of colloidal particles often includes a coagulation step to separate the solid material from the liquid phase. During coagulation, which is typically performed under strong shear flows, clusters of particles are continuously formed, broken, and restructured by the effect of fluid flow. Restructuring, i.e. densification of clusters due to the interactions with the fluid, is a ubiquitous phenomenon, which is still poorly understood, but plays a fundamental role in determining the structure of the final products. In order to better understand the physics of this phenomenon, we have used Stokesian Dynamics simulations to model the fluid-effect on clusters of equal sized spherical particles. First of all, the equations of motion for a rigid colloidal cluster are derived to account for the motion of aggregate of particles in a linear shear flow field. Various colloidal aggregate structures, characterized by different fractal dimensions have been considered. The aggregates are treated as rigid bodies and force distribution over the entire aggregates is found. The hydrodynamic forces acting on each particle in the aggregate are estimated and the particles experiencing hydrodynamic forces greater than the particle-particle adhesive forces are allowed for relative motion with respect to the rest of the aggregate. The effect of shear rate on the restructuring of the aggregates is examined.

Keywords:

Stokesian dynamics, colloidal aggregates, rigid body, shear flow