Simulation of sodium octanoate micelles in aqueous solution

Molecular dynamics calculations have been used to probe the structure of a small sodium octanoate micelle in aqueous solution. The simulation system consisted of 15 octanoate ions, 15 sodium ions and 718 water molecules in a periodically replicated box. Electrostatic interactions were treated with a Ewald method. Two simulations were performed with slightly different models for the water, namely: SPC and SPC/E. Over the course of the roughly 400 ps trajectories, the micelle remained intact with the hydrocarbon chains on the inside and the carboxylate groups on the outer perimeter. The counterion distribution has been examined and compared for the two models. The micelle displayed significant fluctions in shape and had an average radius of about 9 Å. Relatively little water penetrates beyond the head-group region. The average chain conformation in the micelle interior has been compared with that of an isolated monomer in solution.