Interaction between large spheres immersed in small spheres: remarkable effects due to a trace amount of medium-sized spheres

The interaction induced between a pair of large hard spheres immersed in a binary hard-sphere mixture is analyzed using integral equation theories. The mixture consists of dense small spheres containing a trace amount of medium-sized spheres that are smaller than the large ones but much larger than the small ones. With a sufficiently high (but still very low) concentration of the medium-sized spheres, a strongly attractive interaction reaching about two diameters of the medium-sized spheres arises, which makes the interaction range much longer than in a single-component system of the small spheres.