PHASE-BEHAVIOR OF OIL PLUS WATER PLUS NONIONIC SURFACTANT SYSTEMS FORVARIOUS 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 (alpha = 0.5). In this work, experimental phase eq uilibrium data at atmospheric pressure are presented for the systems n onane + water + 2-butoxyethanol at oil-to-water ratios of alpha = 0.12 6, 0.354, 0.568, 0.747, and 0.918, decane + water + 2-butoxyethanol at oil-to-water ratios of alpha = 0.134 and 0.923, and nonane + water 2-(2-butoxyethoxy)ethanol at an oil-to-water ratio of alpha = 0.114. A Landau-type approach, which was developed by Kleinert,(1,2) is furthe r extended and used to fit the data at an oil-to-water ratio of alpha = 0.568 for the system nonane + water + 2-butoxyethanol, at alpha = 0. 134 for the system decane + water + 2-butoxyethanol, and at alpha = 0. 114 for the system nonane + water + 2-(2-butoxyethoxy)ethanol. The fit ted parameters are used for the prediction of the phase behavior at ot her oil-to-water ratios. The predictions by the modified model are in good agreement with the experimental data.