Influence of interfacial properties on perfluorocarbon/aqueous emulsion stability

Abstract

Perfluorocarbon liquid emulsion systems were prepared containing lecithin, mixtures of synthetic phospholipids, cholesterol, cholesterol oleate and Pluronic F68 as emulsifiers. Attempts were made to correlate the stability of the various emulsion systems with their interfacial tension and charge properties. Due to batch to batch variability in the composition of natural egg yolk lecithin, a standard phospholipid mixture was formulated to represent lecithin in these studies. This standard mixture was composed of synthetic analogs of the major molecular species present in lecithin (dioleoyl phosphatidylcholine, dipalmitoyl phosphatidylcholine and dipalmitoyl phosphatidylethanolamine). Egg yolk lecithin and Pluronic F68 were studied for comparison with the standard phospholipid mixture. Analogs of the minor phospholipid species present in lecithin and other surfactant systems were investigated as additives to the standard phospholipid mixture as follows: phosphatidic acid, phosphatidylinositol, phosphatidylserine lysophosphatidylcholine, lysophosphatidylethanolamine, cholesterol, cholesterol oleate and Pluronic F68. Dynamic interfacial tension was determined using a Teflon Wilhelmy plate method (these data were reported in a previous publication). Interfacial charge was determined by microelectrophoresis of the emulsion droplets. Emulsions were prepared using an ultrasonic probe. Emulsion stability was determined by droplet size analysis as a function of time using photon correlation spectroscopy and Coulter analysis. Both thermal stability kinetic studies and sterilization stability studies were conducted. A novel method of assessment of emulsion stability is reported, involving the assignment of points to each emulsion system based on various droplet size parameters.