6533b82cfe1ef96bd128e9df

RESEARCH PRODUCT

Thermodynamic properties of alcohols in a micellar phase. Binding constants and partial molar volumes of pentanol in sodium dodecylsulfate micelles at 15, 25, and 35°C

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Densities of the ternary system water-sodium dodecylsulfate (NaDS)-pentanol and of the binary systems butanol-octane and pentanol-octane were measured at 15, 25, and 35 °C. The apparent molar volume of pentanol in the ternary system was analyzed using a mass-action model for the alcohol distribution in micellar solutions. The partial molar volume of alcohol bound to the micelles and the ratio between the binding constant and the aggregation number of the surfactant are calculated. The partial molar volume binding constant, is discussed in terms of solubilization sites of the alcohol in the micelles whereas the binding constant is compared with that derived from the Nernstian partition constant previously obtained calorimetrically. From the binding constant and Poisson statistics the distribution function of the number of alcohol molecules per micelle, as a function of the concentration of alcohol and of surfactant, are calculated. The derived distribution functions show that a large amount of alcohol can be solubilized in the micelles so that alcoholic mixed micelles can be predicted when the concentration of pentanol is greater than that of NaDS.