Phase behavior of a model surfactant–solvent system at intermediate and high densities

The phase behavior of a binary mixture containing a model surfactant and solvent was determined from lattice Monte Carlo simulations in the grand canonical ensemble using parallel tempering techniques. First and second derivatives of the free energy with respect to the chemical potential (in particular, the density and the isothermal compressibility) were calculated from the combined simulation results through histogram reweighting. Maximums in the isothermal compressibility and heat capacity are observed and it is possible to determine the order–disorder transition temperature; however, they cannot be used to indicate the formation of a hexagonal liquid crystal phase as surfactant concentration increases at constant temperature.