Berlin 2008 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 18: Soft matter

DY 18.3: Talk

Wednesday, February 27, 2008, 14:45–15:00, MA 001

Effective Interactions in Like-Charged Colloidal Mixtures and Cluster Formation — •A. V. Anil Kumar¹ and Juergen Horbach² — ¹Institut für Physik, Universität Mainz, Staudinger Weg 7, 55099 Mainz — ²Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt, 51170 Köln

We consider binary mixtures of like-charged colloidal particles of large size disparity. Using molecular dynamics simulations, the depletion interaction between the big colloidal particles mediated by a fluid of small particles is calulated. Attention is given to the region in parameter space where there is an effective attractive interaction between the large spheres. Our results indicate that indeed there exists an attractive force between two large spheres when the interaction between the large and small spheres are non-additive and highly repulsive. This attractive interaction is due to the overlap of depletion regions around two big spheres formed due to the high repulsion between large and small spheres. The strength of this effective attraction depends on the strength of large-small repulsion and also on the number ratio between the large and small particles. In this attractive region, we simulated a bulk system, where we observed cluster formation among the big particles. The cluster size distribution decays exponentially with cluster size, which is in agreement with experimental observations. At higher volume fractions, the cluster size distribution develops a two peak structure. This may be seen as a precursor to phase separation. The detailed results of molecular dynamics simulations and their connection with experimental observations will be discussed.