ENERGETIC OF SODIUM DODECYLSULFATEDODECYLDIMETHYLAMINE OXIDE MIXED MICELLE FORMATION

Enthalpies of dilution and osmotic coefficients of the sodium dodecylsulfate (NaDS)-dodecyldimethylamine oxide (DDAO) mixtures in water have been measured at 25 and 37-degrees-C, respectively. From the enthalpies of dilution the apparent molar relative enthalpies L(phi) were calculated. The change of the L(phi) vs. total molality m(t) 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 m(t). The excess properties for the mixed micelle formation were evaluated as a function of the mixture composition at some m(t). The profiles are compared with those obtained from thermodynamics of binary liquid mixtures and the regular solution theory.