MICROEMULSION AND LAMELLAR PHASES OF A VECTOR LATTICE MODEL

We examine a three-dimensional vector lattice model for water, oil, and amphiphile mixtures, using the mean-field and Bethe approximations as well as Monte Carlo methods. The Monte Carlo results exhibit three-phase coexistence between water-rich, oil-rich, and microemulsion phases, where the microemulsion has low amphiphile concentration (15%) in agreement with experiment. Also present is a floating incommensurate lamellar phase which coexists with the microemulsion at slightly higher amphiphile concentration, similar to lamellar phases observed experimentally. These features are absent in the two mean-field-like approximations and we conclude that, in general, these types of approximations are inappropriate for describing mixtures containing efficient amphiphiles. © 1995 The American Physical Society.