Recent AFM images demonstrated that a monolayer of cationic surfactants covering a negatively charged surface undergo restructuring in water and form an inhomogeneous charged domain structure, composed of bilayer patches and surfactant-free surface areas. This observation strongly supports the suggestion that long-ranged attraction between two such surfaces is induced by an electrostatic attraction between charged domains. To understand the molecular details of the restructuring process and the domain structure formation, we studied three model systems, each representing a different level of a molecular resolution. The atomistic resolution model was studied by performing a molecular dynamics simulation.  For this model we observed that after around of a hundred of nanoseconds the monolayer got transformed into a spherical micelle floating on the surface. We also performed a simulation using a simple coarse-grained model to study the process dynamics over longer times and larger length scales. This study demonstrated that the surfactant monolayer undergoes restructuring to micelles and then micelles transformed into a bilayer during microseconds of the simulation time. Contrary to experiments, however, we did not observe the formation of positively and negatively charged domains, perhaps due to a short time scale in our simulations compared to the actual time scale in experiments. To overcome the limitations of the coarse-grained simulations, we also developed a simple lattice model consistent with our high-resolution model, and investigated the equilibrium properties of our system.

Computational study of the restructuring process of surfactant-coated surfaces in water

243rd National Meeting (2012)

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