Collision efficiency and colloidal stability of unequal size spherical particles moving through quiescent viscous liquid.

Abstract

Collision efficiencies have been computed for unequal-size spherical particles settling in quiescent viscous liquids, taking into account the hydrodynamic interaction, interparticle attraction and electrostatic repulsion. The results are closely related to the mechanism of coagulation of colloidal particles in a sedimentation field. If the interparticle attraction and electrostatic repulsion are both negligibly small as comparedto viscous drag, the collision efficiency r\ is very small, i.e. about 0.003. However, a relatively large Van der Waals force makes tj greater than unity. As the ratio of the radii of the two particles (smaller divided by larger) decreases the collision efficiency also decreases. The repulsive force between particles determines whether the collision efficiency is zero or larger than zero, but it does not affect the magnitude of the collision efficiency. By including the effect of electrostatic repulsion wewere able to develop criteria which determine the stability (or flocculation) of colloidal particles.