Microscopy, SAXD, and NMR studies of phase behavior of the monoolein-diolein-water system

The phase behavior of the ternary monoolein (MO)-diolein (DO)-water ((H2O)- H-2) system is presented. The experimental phase behavior and microstructur e are studied by a combination of polarizing microscopy, small-angle X-ray diffraction, and NMR methods. Monoolein forms extensive reversed bicontinuo us cubic liquid crystalline phases (C) that are in equilibrium with a lamel lar liquid crystalline phase (L-alpha) on the water-poor side and with exce ss water on the other side. The presence of small amounts of DO in the MO-w ater system is sufficient to destabilize the C and L-alpha liquid crystalli ne phases. Formation of a reversed hexagonal (HII) phase from the cubic pha se occurs at a lower transition temperature than that reported for the MO-w ater system. Within the cubic region, the diamond cubic phase, CD, is less stable than the gyroid type, C-G. The solubility of DO increases within thi s phase when the MO content increases, and the phase reaches its maximum st ability at 4 wt % DO. The large HII-phase formed in the ternary system is i n equilibrium with water, and it solubilizes about 30 wt % DO within its st ability range. A stable dispersion is formed at even higher DO concentratio ns. An ideal swelling of the HII-phase with increasing polar volume fractio n is observed, whereas the length of the hydrocarbon chains along the hexag onal faces is constant. We measure a slight change of the average area per molecule in the H-II-phase with DO concentration. The formation and stabili ty of the liquid crystalline phases can be qualitatively understood from th e self-aggregation model, using the geometrical packing parameter of the li pids.