GEOMETRIC INTERACTIONS IN BINARY COLLOIDAL DISPERSIONS

Small-angle neutron scattering experiments were performed on concentrated binary dispersions of sterically-stabilized poly(methyl methacrylate) particles of size ratio approximately 0.31 dispersed in a mixture of cis-decalin-h18 and octane-d18. Using a contrast match technique, we have, for the first time, studied the local structure of small spheres in a simple (hard-sphere) colloidal mixture. In particular, our experiments demonstrate that the small spheres show evidence of particle clustering. We show that this observation is in accord with a long-ranged attractive force between the small spheres resulting from the depletion of larger particles from between the surfaces of the small spheres.