INVESTIGATIONS INTO THE FORMATION AND CHARACTERIZATION OF PHOSPHOLIPID MICROEMULSIONS .4. PSEUDO-TERNARY PHASE-DIAGRAMS OF SYSTEMS CONTAINING WATER-LECITHIN-ALCOHOL AND OIL - THE INFLUENCE OF OIL

Phase studies have been performed for quaternary systems composed of egg lecithin, cosurfactant, water and oil. The lecithin used was the commercially available egg lecithin Ovothin 200 (which comprises greater than or equal to 92% phosphatidylcholine). The cosurfactants employed were propanol and butanol, and these were used at lecithin/cosurfactant mixing ratios (K-m) of 1:1 and 1.94:1 (weight basis). Six polar oils were investigated, including the alkanoic acids, octanoic and oleic, their corresponding ethyl esters and the medium and long chain triglycerides, Miglyol 812 and soybean oil. All oils, irrespective of the alcohol and the K-m used, gave rise to systems that produced a stable isotropic region along the surfactant/oil axis (designated as a reverse microemulsion system). In addition, the systems incorporating propanol at both K-m and butanol at a K-m of 1.94:1, generally gave rise to a liquid crystalline region and, in some cases, a second isotropic non-birefingent area (designated as a normal microemulsion system). The phase behaviour observed was largely dependent upon the alcohol and K-m used and the size and the polarity of the oil present.