The effect of temperature on the phase equilibria and the types of dispersions of the ternary system composed of water, cyclohexane, and nonionic surfactant

Abstract The phase diagrams of water-cyclohexane systems containing 3 and 7 wt. % of polyoxyethylene (9.7) nonylphenylether have been determined as a function of temperature. In addition to solubilized regions in aqueous and in nonaqueous solutions, the importance of the three-phase realm (water, hydrocarbon, and surfactant phases) has been emphasized. The characteristic temperature at which the mutual solubility of oil and water increases markedly by the aid of nonionic surfactant is closely related to the phase inversion temperature in emulsions. The marked increase in mutual solubility may result from the sandwich-like structure of surfactant, water, and oil layers. The dispersion types of the system have been determined over a wide temperature range. Besides the usual W O type and O W type, W D , D W , D O , O D , and (W+O) D types have been observed, where D represents the surfactant phase. Except for the extreme volume fraction range, the water phase is continuous at low temperature, the oil phase is continuous at high temperature, and the surfactant phase is continuous at a medium temperature near the phase inversion temperature.