Molecular simulation of a dichain surfactant water carbon dioxide system. 2. Self-assembly and aggregation dynamics

We report on the aggregation dynamics of the dichain surfactant [(C7F15)(C7 H15)CHSO4-Na+] + water + carbon dioxide (solvent) system described in our p receding paper. Our results indicate that the aggregation process follows a two-step mechanism: hydration of anionic headgroups and Na+ counterions fo llowed by aggregation of hydrated surfactant molecules. The kinetics of agg regation is consistent with the Smolouchowski theory of diffusion-limited a ggregation, though on a much faster time scale compared to aggregation obse rved in aqueous surfactant systems. This is attributed to the fact that the intermolecular interactions responsible for aggregation in the system unde r investigation are electrostatic in nature and the carbon dioxide permits faster diffusion of surfactant molecules than water. The surfactant tails f orming the corona of the aggregates provide steric stabilization of the agg regates thereby reducing the rate of aggregation.