Effective interaction between large colloidal particles immersed in a bidisperse suspension of short-ranged attractive colloids

The effective force between two large hard spheres mimicking lyophobic colloids (solute) immersed in an asymmetric two-component mixture of smaller particles (solvents), interacting via Baxter's sticky hard sphere (SHS) potential, was studied using integral equation theory and Monte Carlo simulation. The theoretical predictions were calculated from the analytic solution of the Percus-Yevick/Ornstein-Zernike integral equation for spatial correlations in a three-component mixture at vanishing solute concentration, while the simulation results were obtained by applying a special simulation technique developed for sampling the hard-sphere collision force. Due to layering of the solvent molecules, the effective force between the particles of the solute oscillates with periods equal to the molecular diameters of both solvent components. The attractive force between the solute particles in the SHS mixture comprising strongly attractive molecules of either component decays slower than that in the mixture with weaker interparticle attraction. Similar features are also observed when inspecting the separate contributions of individual components to the total solute-solute force. At sufficient strength of the interparticle stickiness, these oscillations disappear, the force becoming long ranged and attractive at all separations.