Depletion and structural forces between two macrosurfaces immersed in a bidisperse colloidal suspension

Recent experiments on the thinning of liquid films formed from colloidal su spensions carried out in our laboratory [Nikolov, A., and Wasan, D. T., J. Colloid Interface Sci. 133, 1 (1989); Langmuir 8, 2985 (1992)] have reveale d the pronounced effect of the presence of bidisperse-sized particles on th e film stability. To shed more light on the role of the size bidispersity o n the film properties, we performed a statistical mechanics study of a mode l system that consists of a binary hard-sphere mixture with a size ratio of 1: 10 between two planar surfaces. The variations of the particle local de nsities, excess surface coverage, film disjoining pressure, and film intera ction energy per unit area with separation between the surfaces in the pres ence of monodisperse and bidisperse particles have been investigated. A rep ulsive depletion interaction (depletion stabilization) between the surfaces in the case of a bidisperse suspension has been observed at separations of about one layer of the larger particles. (C) 2001 Academic Press.