Interaction between a macrosphere and a flat wall mediated by a hard-sphere colloidal suspension.

The interaction between the macrosphere and the flat wall immersed in a binary fluid comprising small and large (size ratio around 1:10) hard spheres has been investigated. We find that the presence of the highly size-asymmetric particles qualitatively modifies the induced excluded-volume interaction between the macrosphere and the flat wall compared to that observed in a single-component suspending fluid comprised of only large or only small species. The role in the interaction between a macrosphere and a flat wall played by species of the fine component that usually is approximated by a continuum medium (primitive description of a bidisperse fluid) is emphasized. Particularly, we show that taking into account the smaller component of a bidisperse suspending fluid modifies significantly the macrosphere-wall depletion attraction that is predicted when only large particles are taken into account. The depletion attraction force created by the presence of small fluid particles enhances the adsorption of large particles and their structuring on the wall.