Effect of water on the local electric potential of simulated ionic micelles.

Ionic micelles in an aqueous solution containing single-charged counter-ions have been simulated by molecular dynamics. For both cationic and anionic micelles, it has been demonstrated that explicit description of solvent has strong effect on the micelle's electric field. The sign of the local charge alters in the immediate vicinity of the micellar crown and the electric potential varies nonmonotonically. Two micelle models have been examined: the hybrid model with a rigid hydrocarbon core and the atomistic model. For three molecular models of water (Simple Point Charge model (SPC), Transferable Intermolecular Potential 5- Points (TIP5P) and two-centered S2), the results have been compared with those for the continuum solvent model. The orientational ordering of solvent molecules has strong effect on the local electric field surprisingly far from the micelle surface.

Principal role of the stepwise aggregation mechanism in ionic surfactant solutions near the critical micelle concentration. Molecular dynamics study.

The validity of the assumption on the predominant contribution of the stepwise processes to the ionic micelle formation/destruction in the vicinity of critical micelle concentration was investigated by molecular dynamics simulation. A coarse-grained model was used to describe the surfactant/water mixture. The cluster size distribution was estimated directly from molecular dynamics simulations or obtained from a reduced set of kinetic equations. The good agreement between two approaches shows that the neglect of the terms responsible for cluster fusion/fission is fully justified and that such processes are less important than stepwise aggregation.