Thermodynamics of precipitation from mixed micellar solutions

The equilibrium of the precipitate with mixed micellar solutions of the fol lowing types, (1) two ionic surfactants with the same hydrophobic chain but different counterions and (2) anionic + semipolar surfactants, are conside red. Simple thermodynamic models that yield the composition dependence of t he dissolution temperature in the ternary system (at fixed overall surfacta nt content) are discussed. The description is performed in terms of composi tion variables of aqueous pseudo phase (solubility product approach) or mic ellar pseudo phase. The latter approach has appeared efficient for predicti on of solubility diagrams in concentrated ternary systems with the use of d ata for aqueous solutions of pure surfactants. Results of calculations are compared with experimentally studied solubility diagrams for mixed aqueous systems of (1) dodecylsulfates of sodium and magnesium and (2) sodium dodec ylsulfate + dodecylamine oxide. The mixtures are studied at overall surfact ant contents significantly higher than the CMC. (C) 1999 Elsevier Science B .V. All rights reserved.