Formation of lecithin-based microemulsions containing n-alkanol phosphocholines

The formation of microemulsion phases was studied at 25°C for systems containing soybean phosphatidylcholine (lecithin), medium-chain-triacylglycerol (MCT) or isopropyl myristate (IPM), water, alcohol and n-alkanol phosphocholines (Cn), with chain length between 6 and 12 carbon atoms, as second hydrophilic surfactant. The lecithin/Cn mixing ratio was 1:1, while the surfactant/alcohol mixing ratios were 1:1 and 2:1 for the systems containing MCT, and 1:1 for the systems containing IPM. Alcohols used were ethanol, 1-propanol and 1-butanol. The maximum extension of the region of existence of the microemulsion systems containing MCT was found with butanol, while in the presence of IPM it was found with propanol. Except for the system containing IPM and butanol, the size of the microemulsion phase increased on increasing the length of the Cn chain, and moved towards the aqueous corner of the phase diagram. The use of a second hydrophilic amphiphile to adjust the spontaneous packing properties of the lecithin-alcohol system, or to increase the fluidity of the surfactant film, provided an increase in the region of existence of the microemulsion systems. Copyright (C) 1998 Elsevier Science B.V.