Self-Assembly of surfactants in nanopores: a dissipative particle dynamics study

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In recent years dissipative particle dynamics (DPD) has been established as a powerful and versatile computer simulation technique by which dynamical processes in macromolecular self-assembling systems can be studied. We plan to apply DPD to investigate the dynamics of micelle formation in water-surfactant mixtures near solid surfaces or in idealized mesoporous media like MCM-41-type of materials. In order to access the relevant length and time scales of about 100 nm and 1 µs, respectively, both surfactant and water molecules are described on the basis of coarse-grained models; conservative forces between the resulting "effective particles" are then supplemented by stochastic and dissipative forces reflecting the presence of rapidly varying internal degrees of freedom. The focal point of the present project is to understand single-particle and collective dynamics in the vicinity of the critical surface aggregation concentration (CSAC) of strong amphiphiles at solid surfaces and in nanopores. Experimentally, the sharp increase of the adsorption excess for concentrations slightly above the CSAC is ascribed to surface-induced micelle formation. Shape and size of these aggregates are suspected to strongly depend not only on the architecture of the surfactant itself, but also on the degree of hydrophility and (particularly in narrow pores) on the curvature of the pore walls. By means of DPD computer simulations the dynamics of the micelle formation and its interplay with properties of the confining substrate are investigated. Thermodynamic and structural features are explored in the experimental (Findenegg) and theoretical (Gubbins) projects of this application package.