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RESEARCH PRODUCT

Thermodynamics of Solubilization of Pentanol in Sodium Dodecyl Sulfate-Dodecyldimethylamine Oxide Mixed Micelles

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Abstract Heat capacity and density measurements of pentanol (PeOH)-sodium dodecyl sulfate (NaDS)-dodecyldimethylamine oxide-water mixtures were carried out at 0.03 m PeOH as a function of the total surfactants concentration (mc) at different ratios (XNaDS). From experimental data, the apparent molar volumes (VΦ,R) and heat capacities (CΦ,R) of PeOH in the surfactants mixture solutions were calculated. As a general feature, at a given mixture composition, VΦ,R increases monotonically with mt as observed in pure surfactants. In the cases of XNaDS = 0.1 and 0.3, VΦ,R drops at about 0.1 and 0.15 mt respectively. The decreasing CΦ,R VS mt curve shows peculiarities which were ascribed to the presence of a liquid crystalline phase for XNaDS = 0.1 and 0.3 and of a structural micellar transition for XNaDs = 0.6 and 0.9. At a given XNaDS, the dependence of the apparent molar property of PeOH on mt was rationalized in terms of the distribution constant of alcohol between the aqueous and the micellar phases (K) and its partial molar property in the aqueous and the micellar phases. The standard free energy, calculated from the K values, and the partial molar properties of PeOH in the surfactant-surfactant micelles change linearly with XNaDS according to the ideal behavior.