8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Wed 711:10-14:00P5.79Effective forces in mixtures of short-ranged attractivecolloids: theory and simulationAndrej Jamnik 11 Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5,1000, Ljubljana, SloveniaThe effective force between a pair of large colloidal (solute) particles immersed in an asymmetrictwo-component mixture of smaller particles (solvents), interacting via Baxter’s sticky hard sphere(SHS) potential [1], has been studied using integral equation theory and Monte Carlo simulation[2]. The theoretical predictions have been calculated from the analytic solution of the Percus-Yevick/Ornstein-Zernike integral equation for spatial correlations in a three-component mixtureat vanishing solute concentration, while the simulation results have been obtained by applying aspecial simulation technique developed for sampling the hard-sphere collision force [3]. Due tolayering of the solvent molecules, the effective force between the particles of the solute oscillateswith periods equal to the molecular diameters of both solvent components. The attractive forcebetween the solute particles in the SHS mixture comprising strongly attractive molecules of eithercomponent decays slower than that in the mixture with weaker inter-particle attraction. Similarfeatures are also observed when inspecting the separate contributions of individual components tothe total solute-solute force. At sufficient strength of the inter-particle stickiness, these oscillationsdisappear, the force becoming long-ranged and attractive at all separations. In addition, the bigsmallinteractions are modeled also as hard core pair potentials with attractive or repulsive Yukawatail leading to the accumulation repulsion and depletion attraction between the two colloids, respectively.[1] R. J. Baxter, J. Chem. Phys. 49, 2770 (1968).[2] A. Jamnik, J. Chem. Phys. 128, 234504 (2008).[3] J. Z. Wu, D. Bratko, H. W. Blanch, J. M. Prausnitz, J. Chem. Phys. 111, 7084 (1999).79