Characterization of the liquid-crystalline phases in the glycerol monooleate/diglycerol monooleate/water system

The ternary phase diagram of two nonionic polar lipids, glycerol monooleate (GMO) and diglycerol monooleate (DGMO), in water has been characterized through NMR, polarizing optical microscopy, SAXS, and rheological measurements. GMO in water forms a lamellar and two types of bicontinuous cubic phases. The diamond type exists in equilibrium with water. DGMO, with its bulky polar group, forms only lamellar structures that also coexist with water. In the ternary GMO/DGMO/water system, the regions of lamellar and cubic phases are significantly enlarged, and a swollen cubic phase of the gyroid type exists in equilibrium with water. Measurement of the viscoelastic properties revealed that the cubic phases are elastic, independent of the sample composition. The cubic phases become softer (the G' storage modulus decreases) with increasing water and DGMO content. A discontinuity is observed in the G' versus water content graph at the transition between the gyroid and the diamond cubic phases.