Model for bulk phases in mixtures of amphiphilic molecules and water

We present a one parameter spin model for mixtures of amphiphilic molecules and water which is distinct from earlier models for the phase behavior of these systems. We show that the model on a two-dimensional square lattice supports ‘‘lamellar,’’ ‘‘cubic,’’ and ‘‘micellar’’phases somewhat like those observed experimentally. We present Monte Carlo data on the lamellar-isotropic line in the phase diagram in the temperature-chemical potential plane. We summarize the features of the phase diagrams which we have found for the two cases in which the directionality of the amphiphilic molecules in the model are represented by two component (xy-like) and three component (Heisenberg-like) spins, respectively.