ROLE OF DEPLETION AND SURFACE-INDUCED STRUCTURAL FORCES IN BIDISPERSESUSPENSIONS

Depletion and structural interactions between dilute, large, nearly ha rd-sphere colloidal particles in a fluid dispersion containing much sm aller nearly hard spheres were investigated as a function of small-par ticle concentration in sedimentation experiments. It shows that low co ncentrations of fine particles can destabilize larger particles due to the attractive depletion forces, while at higher concentrations of sm all particles, the surface-induced structural forces prevent large-siz e particles from approaching each other and thereby stabilize the larg e-particle suspension. A theoretical model based on the Ornstein-Zerni ke method was used to calculate the interparticle interactions in a bi dispersed colloidal system in which small particles are polydispersed. The theoretical results explain the experimental observations.