Fluctuation-induced interactions in colloidal suspensions

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Based on previous and current work in our group, in this project we want to develop a simulation method for many-particle systems interacting through fluctuation-induced critical Casimir forces. In contrast to previous theoretical work, the critical Casimir forces are modeled quasi "ab initio", as the fluctuating medium inducing these forces is exactly taken into account using appropriate statistical methods. Hence the origin of the fluctuation-induced forces is included in the method without any approximations. The cluster Monte Carlo algorithm developed in a current master thesis shall be used to model colloidal suspensions within critical binary liquid mixtures, which show a great variety of effects in experiments. Especially we want to study the influence of the particles on the critical medium and how the phase transition in the medium is modified.Fluctuation-induced interactions such as critical Casimir forces are generally non-additive and therefore can only approximately be described as sum of two-body interactions. Using the proposed method we want to analyze the accuracy of this approximation and the importance of higher order contributions such as three-body terms.At the beginning of the project the cluster Monte Carlo algorithm shall be enhanced in several ways (e.g. extension to three space dimensions, inclusion of varying surface couplings). Then the critical behavior of both the particle system and the fluctuating medium shall be characterized. Furthermore, many-particle effects shall be investigated resulting from the non-additivity of the fluctuation-induced forces which are important near the critical point of the medium. Finally the studies shall be extended to polydisperse systems and to Janus particles, where a rich behavior is expected.