| Abstract
| - Using an atom based force field, molecular dynamics (MD) simulations of 54 dodecylphosphocholine (DPC)surfactant molecules in water at two different concentrations above the critical micelle concentration havebeen performed. Starting from a random distribution of surfactants, we observed the spontaneous aggregationof the surfactants into a single micelle. At the higher DPC concentration (0.46 M) the surfactants aggregatedinto a worm-like micelle within 1 ns, whereas at lower concentration (0.12 M) they aggregated on a slowertime scale (∼12 ns) into a spherical micelle. The difference in the final aggregate is a direct consequence ofthe system achieving the lowest free energy configuration for a given quantity of surfactant within the periodicboundary conditions. The simulation at low surfactant concentration was repeated three times in order toobtain statistics on the rate of aggregation. It was found that the aggregation occurs at a (virtually) constantrate with a rate constant of k = 1 × 10-4 ps-1. This is an unexpected result. On the basis of Monte Carlosimulations of a stochastic description of the system, using diffusion rates and cluster radii as determined byseparate MD simulations of single DPC clusters, a lower rate constant which diminishes in the course of theaggregation process had been predicted. Neglect of hydrodynamic interactions, of long-range hydrophobicinteractions, or of spatial correlations in the stochastic approach might account for the descrepancies with themore accurate MD simulations.
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