HYDRODYNAMIC INTERACTIONS BETWEEN 2 SPHERES NEAR A SOLID PLANE

Hydrodynamic interactions between particles deposited on a solid wall and those free to move in a simple shear or a stagnation point flow were studied by the boundary element method. There are two effects which can play an important role during deposition, namely: (i) disturbance of the particle trajectories by the deposited particles; and (ii) an extra hydrodynamic force on a deposited particle during a two-body encounter. The first effect slows down the deposition rate on the collector surface (blocking), while the second effect can increase particle removal from the surface. We have shown that hydrodynamic effects cannot explain the large blocking effects commonly observed; these must be due to colloidal interactions, not included in this paper. However, the force exerted on a deposited particle can be changed considerably when a second particle collides with it under purely hydrodynamic conditions. This effect is likely to be responsible for the removal of weakly-bound particles