Binary phase equilibria and structure of the two alpha-methyl-substituted surfactants sodium (R)-2-methyldecanoate and racemic sodium 2-methyldecanoate

In this study, we present the binary phase diagrams for the aqueous systems of the alkyldecanoic salts racemic sodium 2-methyldecanoate and sodium (R) -2-methyldecanoate, respectively. Both systems form a micellar solution pha se, as well as a normal hexagonal, a cubic, and a lamellar liquid crystalli ne phase. They also form a very narrow intermediate phase, situated between the hexagonal and cubic liquid crystalline phases. The methods used for ch aracterization were crossed polaroids, polarizing optical microscope and H- 2 NMR quadrupolar splittings combined with SAXS studies. The cubic phase ga ve a well-resolved SAXS diffraction pattern, with eight peaks present, whic h establishes the bicontinuous cubic structure as Ia3d. A significant diffe rence in these two phase diagrams, compared to those of unsubstituted alkan oates with the same chain length, is the very low Krafft boundary.