INVESTIGATIONS INTO THE FORMATION AND CHARACTERIZATION OF PHOSPHOLIPID MICROEMULSIONS .3. PSEUDO-TERNARY PHASE-DIAGRAMS OF SYSTEMS CONTAINING WATER-LECITHIN-ISOPROPYL MYRISTATE AND EITHER AN ALKANOIC ACID, AMINE, ALKANEDIOL, POLYETHYLENE-GLYCOL ALKYL ETHER OR ALCOHOL AS COSURFACTANT

The phase behaviour of quaternary systems composed of lecithin/isopropyl myristate/water/cosurfactant, at a lecithin: cosurfactant mixing ratio (K-m) of 1:1 (on a weight basis) have been investigated by the construction of phase diagrams. The lecithin used in this study was the commercially available soybean lecithin, Epikuron 200 (purity greater than 94% phosphatidylcholine) and the cosurfactants examined were either short (alkyl chain length 4-6) straight-chain alkanoic acids, amines, alkanediols, diethylene glycol alkyl ethers or alcohols. With the exception of the amines which appeared to react with lecithin, all the systems showed the area of existence of a stable isotropic region along the surfactant/oil axis (i.e., reverse microemulsion area; L(2)). In no case was a second isotropic region (i.e., normal microemulsion area; L(1)) observed, although in certain systems a single clear isotropic region covered virtually the whole of the phase diagram and may have included an L(1) region. A liquid crystalline (LC) region was observed only in systems containing either an alkanediol or polyethylene glycol alkyl ether as cosurfactant. It was concluded that the area of existence of the various phase regions was very dependent upon the nature of the cosurfactant used.