Fluid bilayer phase in aqueous mixtures of fatty alcohol and cationic surfactant

Lamellar gel networks are creamy formulations extensively used in cosmetics and pharmaceutics. The basic units of these networks are lipid bilayers assembled from mixtures of fatty alcohols, surfactants, and water. Despite being an essential step for the preparation of the dispersions, the nature of the mixtures at high temperature has defied understanding. Here we show, by atomistic molecular dynamics simulations, that aqueous mixtures of cetyl (C_{16}OH) and stearyl (C_{18}OH) alcohols, and cetyl-trimethylammonium chloride (CTAC), lead to fluid bilayers, which are the units of the lamellar L_{α} phase. By providing a consistent numerical simulation model able to describe the structure and properties of fatty alcohol lamellae stabilized by a surfactant, our work paves the way for the elucidation of the forces regulating this family of industrially important gels.