6533b873fe1ef96bd12d4abb

RESEARCH PRODUCT

Enthalpies of solution and dilution of butanol and pentanol in dodecyltrimethylammonium bromide micellar solutions

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The enthalpies of solution and of dilution of 1-butanol and 1-pentanol were measured in micellar solutions of dodecyltrimethylammonium bromide by systematically changing the concentration of alcohols and surfactant. The enthalpies of solution at infinite dilution of alcohols at each surfactant concentration were evaluated from a linear plot. This quantity increases with surfactant concentration (up to 0.8m) with a curvature which depends on the alcohol alkyl chain length. The difficulties arising for a quantitative treatment of both the enthalpies of dilution and of solution at finite alcohol concentrations are discussed. The dependence on the surfactant concentration of the standard enthalpies of solution and the enthalpies of dilution for m→0 are rationalized. From the resulting equations the distribution constant, standard enthalpy of transfer, standard enthalpy of solution, and the alcohol-alcohol interaction parameter in the micellar phase are evaluated. The enthalpies of transfer obtained using this technique agree well with those previously reported from enthalpies of mixing. The distribution constants also agree with those reported in the literature from several approaches: mixing enthalpies, partial molar volumes, and the dependence of the cmc on added alcohol.