Microemulsions and liquid crystalline formulated with triacylglycerols: Effect of ethanol and oil unsaturation

Pseudo-ternary phase diagrams were constructed in order to evaluate the effect of the prevailing oil unsaturation and cosurfactant concentration on the phase behavior of systems prepared with sunflower oil or high oleic sunflower oil (HOSO), water, Tween 80 and ethanol. The phase diagrams showed small areas of one single translucid phase with production of water-in-oil (L2) and oil-in-water (L1) microemulsions. A higher cosurfactant concentration increased microemulsion area and allowed solubilize more water using lower surfactant content. Moreover, small angle X-ray scattering (SAXS) measurements showed that depending of the composition the surfactant self-assembly led to lamellar (Lα) or hexagonal (H1) structures. Microemulsions showed Newtonian behavior, while Lα and H1 showed shear-thinning behavior, viscoelasticity and thixotropy. This more complex rheological behavior was accentuated at lower cosurfactant concentration and with the less unsaturated oil, showing that both oil unsaturation and ethanol content exerted influence on systems properties. However, the higher concentration ethanol masked the effect of oil unsaturation.