6533b7d5fe1ef96bd1263b47

RESEARCH PRODUCT

Energetics of sodium dodecylsulfate-dodecyldimethylamine oxide mixed micelle formation

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Enthalpies of dilution and osmotic coefficients of the sodium dodecyl-sulfate (NaDS)-dodecyldimethylamine oxide (DDAO) mixtures in water have been measured at 25 and 37°C, respectively. From the enthalpies of dilution the apparent molar relative enthalpies LΦ were calculated. The change of the LΦ vs. total molality mt profiles with the mole fraction reflects the variation of the ionic character of the mixed micelles. From the osmotic coefficients the nonideal free energy G2ni were calculated. By combining G2ni with the partial molar relative enthalpies, the nonideal entropies TS2ni were determined. At a given mole fraction, G2ni and TS2ni values are decreasing and increasing respectively, tending to become constant at high mt. The excess properties for the mixed micelle formation were evaluated as a function of the mixture composition at some mt. The profiles are compared with those obtained from thermodynamics of binary liquid mixtures and the regular solution theory.