Molecular dynamics simulations of a sodium octanoate micelle in aqueous solution

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Abstract
Molecular dynamics simulations of a sodium octanoate micelle in aqueous solution are reported. Simple analytical expressions have been used for the interatomic interactions, including a Lennard‐Jones term and a Coulombic interaction betwen partial charges on each site. Two different interaction potentials have been investigated, and amphiphilic aggregation is shown to depend strongly on the electrostatic properties of the water model. For both potentials the micelle shows a broad transition region between the aqueous and hydrocarbon regions. The hydration of different carbon atoms in the chain is largest for the carboxylic atom, then decreases along the chain, reaching a minimum and then increases again at the end of the chain. The micellar translational and rotational diffusion are too fast, probably due to deficiencies in the water model. The rotational diffusion of the entire micelle is found to be an order of magnitude slower than that of the monomers. Reorientational time correlation functions and order parameters for C–H vectors in the chains are reported and agree qualitatively with a recently proposed two‐step model for NMR relaxation in micelles. The dynamics of water molecules close to the micellar surface is found to be similar to bulk water.