Simulation of a sodium dodecylsulfate micelle in aqueous solution

Molecular dynamics calculations have been used to probe the structure of a small sodium dodecylsulfate micelle in aqueous solution. The simulation system consisted of 42 dodecylsulfate ions, 42 sodium ions, and 1901 deuterated water molecules in a periodically replicated box. Electrostatic interactions were treated with an Ewald method. Over the course of a 182 ps trajectory, the micelle remained compact and roughly spherical with the hydrocarbon chains on the inside and the sulfate groups on the outer perimeter. The micelle displayed only small fluctuations in shape and had an average radius of about 15 Å. Relatively little water penetrated beyond the head-group region and the inner core (9 Å in radius) was devoid of water. On average each chain was found to have about three gauche defects. The average chain conformation in the micelle interior has been contrasted with that of an isolated monomer in solution. The counter ion distribution has been examined and compared with results from a previous simulation of a sodium octanoate micelle.