Phase behavior of oil/water/nonionic surfactant systems

The phase behavior of oil/water/nonionic surfactant systems under the effect of temperature is usually only measured at an oil-to-water ratio of 1 : 1 (alpha = 0.5). It was found that with increasing oil-chain length and increasing hydrophilicity of the surfactant (Triton X-114 to Triton X-100), the three-phase region widens toward higher temperatures. The clear inclination of the "fishes" at constant oil-to-water ratios shows that the surfactant becomes more hydrophobic with increasing temperature. It was observed that the phase behavior of systems changes with the amount and kinds of added salts. The description of the experiments by the modified Landau-type model is satisfactory.