Dispersions of liquid crystalline phases of the monoolein/oleic acid/pluronic F127 system

Aqueous dispersions of lyotropic liquid crystalline phases (cubosomes and hexosomes) were prepared using lipid mixtures, monoolein (MO) and oleic acid (OA), and emulsifier Pluronic F127 by changing their composition. The size and internal structure of the prepared particles were characterized by dynamic light scattering and small-angle X-ray scattering, respectively. At the weight ratio of MO:OA = 5:5 and 8 wt % F127 to the total lipid mixtures, particles with a diameter of ca. 140 nm and including an inverted hexagonal (H_II) phase were formed. With an increase in the F127 concentration, the particle size decreased, but the internal structure (lattice constant) did not change, suggesting that F127 absorbs at the particle surface with little incorporation in the H_II phase. The lipid ratios and solvent pH strongly affected the morphology of the internal structure of the particles. By increasing the weight fraction of OA in the lipid mixtures, the internal structure transformed in the order of bicontinuous cubic-inverted hexagonal-inverted cubic. In addition, transformation from the cubosome to the hexosome was observed by decreasing the pH, suggesting that the interior of the nanoparticles is responsive to the outer environment.