Phase Behavior of Oil + Water + Nonionic Surfactant Systems for Various Oil-to-Water Ratios and the Representation by a Landau-Type Model

The phase behavior of oil + water + nonionic surfactant systems under the influence of the temperature is usually only measured at an oil-to-water ratio of 1:1 (α = 0.5). In this work, experimental phase equilibrium data at atmospheric pressure are presented for the systems nonane + water + 2-butoxyethanol at oil-to-water ratios of α = 0.126, 0.354, 0.568, 0.747, and 0.918, decane + water + 2-butoxyethanol at oil-to-water ratios of α = 0.134 and 0.923, and nonane + water + 2-(2-butoxyethoxy)ethanol at an oil-to-water ratio of α = 0.114. A Landau-type approach, which was developed by Kleinert, , is further extended and used to fit the data at an oil-to-water ratio of α = 0.568 for the system nonane + water + 2-butoxyethanol, at α = 0.134 for the system decane + water + 2-butoxyethanol, and at α = 0.114 for the system nonane + water + 2-(2-butoxyethoxy)ethanol. The fitted parameters are used for the prediction of the phase behavior at other oil-to-water ratios. The predictions by the modified model are in good agreement with the experimental data.