Effect of Adding Isopropyl Myristate to Microemulsions Based on Soybean Phosphatidylcholine and Triglycerides

Abstract

The effect on the phase behavior and microstructure of pharmaceutically interesting microemulsions which is produced by adding isopropyl myristate (IPM) to the systems is described. The microemulsions are based on water, 1-propanol, soybean phosphatidylcholine (SbPC), and two different triglycerides; a medium-chain triglyceride (C8−C10) and a long-chain triglyceride (soybean oil). When IPM was added to the triglyceride oil phase, the spontaneous curvature of the surfactant film decreased and the flexibility of the surfactant monolayer increased. The change in spontaneous curvature was manifested by a gradual change in the microstructure of the microemulsion, as revealed by NMR self-diffusion data, from an oil-in-water type of structure at low concentrations of IPM to an oil continuous structure at higher IPM concentrations. At intermediate IPM concentrations, the microstructure was found to be of a bicontinuous nature. By optimizing the amount of IPM and the 1-propanol concentration, one-phase microemulsions containing equal amounts of water and oil can be obtained at lower surfactant concentrations and lower 1-propanol concentrations, compared with those for a system with only the triglyceride as the nonpolar phase.