Phase behaviour of microemulsion systems containing lecithin and lysolecithin as surfactants

Phase diagrams were constructed at 25 degrees C to investigate the phase behaviour of systems containing water, isopropyl myristate, commercially-available soybean lecithin and lysolecithin at different mixing ratios, as surfactant mixture, and alcohol, as cosurfactant. Lysolecithin was obtained by enzymatic hydrolysis from soybean lecithin. The lysolecithin:lecithin mixing ratios were 0.7:1, 1.4:1 and 2.1:1, for the systems containing 1-butanol, and 1.4:1, for the systems containing 1-propanol or ethanol. The surfactant/cosurfactant mixing ratios (Km) were 1/2, 1/1 and 2/1 for 1-butanol, 1/1 and 1/2 for 1-propanol and ethanol. A liquid crystalline region was observed only in systems containing 1-butanol at Km 2/1. The stability range of microemulsions containing lecithin was greatly increased by adding lysolecithin. The extension of the microemulsion domain was very dependent upon the nature of the cosurfactant and on the lysolecithin:lecithin and surfactant/cosurfactant mixing ratios. Infinitely dilutable microemulsions were obtained using 1-propanol or ethanol.