Collision efficiency of equal spherical particles in a shear flow. The influence of London-van der Waals forces

Abstract

A theoretical and experimental approach to the investigation of the influence of London-Van der Waals forces on orthokinetic flocculation is described. The theoretical treatment evaluates the effect of these forces on the interaction of two spherical particles in a laminar shear flow, to give a value of the collision efficiency (stability ratio). The experimental measurements on the flocculation of monodisperse polystyrene beads in a laminar shear flow reported provide a test of the theory. By making use of the theoretical approach described in this paper the London-Hamaker constant for polystyrene in aqueous suspension can be calculated from measurements of orthokinetic flocculation : the values obtained are in good agreement with those derived by other methods. The method additionally provides a means of measuring the “characteristic wavelength” of these forces.