The colloidal properties of fluorocarbon emulsions

Some of the colloidal aspects of perfluorochemical emulsions have been investigated. Particular attention was given to the influence of the nature of the oil phase on emulsion stability. Bulk emulsion stability was measured by an electron micrographic technique. Interfacial and single droplet rest-time data were also collected. A range of surfactants and perfluorochemicals were investigated. It was found that emulsion stability depends on the chemical nature of the oil phase and the emulsifier. The differences in stability could be rationalized in terms of the intermolecular forces between oil molecules, and oil and surfactant molecules. The effect on stability of a small amount of an additive incorporated into the oil phase was also investigated. It is postulated that although coalescence is the main mechanism by which fluorocarbon emulsions coarsen, molecular diffusion (Ostwald Ripening), in the more stable systems, is also important. Most stable emulsions were obtained by utilizing an emulsifier system comprising a small and a large molecular weight emulsifier. Accelerated stability testing and optimum storage conditions were also investigated. About 40C was found to be the optimum storage temperature. The problem of the fluoride ion production during emulsification could be minimised by sonicating in a carbon dioxide atmosphere. The oxygen uptake and release by fluorocarbon emulsions was rapid, reaching equilibrium within half a second. The in-vitro phagocytosis experiments showed that the phagocytosis rate of fluorocarbon emulsions was dependent on the droplet diameter and its surface characteristics. Investigation of methods to sterilize the fluorocarbon emulsions showed that filtration of constituents before emulsification coupled with autoclaving had the minimum effect on stability. A qualitative correlation between single droplet stability and bulk emulsion stability was found and it is concluded that the method could be a useful screening procedure to find an optimum system