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 (HII) 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 HII 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.

We report the nanostructures in a novel microemulsion system of silicone oil, water and a surfactant mixture of an anionic and a nonionic surfactant. The phase diagram of the investigated system exhibits two isotropic single-phase channels for constant temperature. The upper channel, that is the channel with the higher mass fraction of nonionic surfactant, starts with an L 3 -phase at the water side, and passes through a minimum continuously to the oil side. The channel with the lower mass fraction of nonionic surfactant starts with an L 1 -phase at the water side, and passes with increasing oil content and increasing mass fraction of nonionic surfactant to the middle of the phase diagram and ends there. No connection between the two channels was detected at a surfactant concentration of 15%. The two channels are separated by a single L a -phase and multiphase regions. In contrast to the results from microemulsions with nonionic surfactants, cryo-TEM micrographs on this system show that the upper phase channel has a bicontinuous structure from zero to only about 35% of oil. At higher oil content the channel contains water droplets in a continuous oil phase. At a water/oil ratio of 1 : 1, the structure looks like a polyhedral foam structure or a high internal phase emulsion (HIPE) structure, and not like the usual bicontinuous structure, as generally assumed. Nevertheless, the dimensions of the imaged bicontinuous and water-in-oil-structures were consistent with the theoretical consideration for nanostructures in microemulsions. The lower channel with its o/w-structure could not well be imaged with the cryo-TEM method. Instead of small droplets, small vesicles were imaged, that obviously were formed by the loss of oil in the thin film during the specimen preparation process for cryo-TEM.

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