Cubic Phase Prepared in an Anionic/Amphoteric Surfactant/Oleic Acid/Decane/Water System and the Relationship with the Neighboring Phase

The formation, properties, and structure of discontinuous cubic phase in the pseudo-ternary system consisting of N‘-carboxyethyl N‘-hydroxyethyl N-aminoethyl dodecylamide (imidazoriniumbetain), sodium and triethanol amine salt of polyoxyethylene (1.5 mol) myristyl ether sulfate, oleic acid, decane, and water at a constant surfactant/water ratio of 4/6 were studied by means of small-angle X-ray scattering, freeze-fracture transmission electron microscopy, static light scattering, and dynamic rheology to gain an insight in its origin and interrelation with neighboring phases. It was found that the cubic phase occupied a rather wide region in a constructed ternary phase diagram, including from 25 to 45% of decane. Its properties and structural parameters varied with changing the oil content. The decane addition caused the swelling of spherical micellar aggregates. This resulted in an increase of their diameter up to 35 nm, which was ca. nine times larger than that of the initial micelles, and micellar volume...