PHASE-BEHAVIOR OF MICROEMULSION SYSTEMS CONTAINING LECITHIN AND LYSOLECITHIN AS SURFACTANTS

Phase diagrams were constructed at 25 degrees C to investigate the pha se behaviour of systems containing water, isopropyl myristate, commerc ially-available soybean lecithin and lysolecithin at different mixing ratios, as surfactant mixture, and alcohol, as cosurfactant. Lysolecit hin was obtained by enzymatic hydrolysis from soybean lecithin. The ly solecithin: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) w ere 1/2, 1/1 and 2/1 for 1-butanol, 1/1 and 1/2 for 1-propanol and eth anol. A liquid crystalline region was observed only in systems contain ing 1-butanol at Km 2/1. The stability range of microemulsions contain ing lecithin was greatly increased by adding lysolecithin. The extensi on of the microemulsion domain was very dependent upon the nature of t he cosurfactant and on the lysolecithin:lecithin and surfactant/cosurf actant mixing ratios. Infinitely dilutable microemulsions were obtaine d using 1-propanol or ethanol.