Interfacial properties and emulsion stability in fluorinated oil—non-fluorinated oil—surfactant(s) systems

The formation of interfaces and emulsions in systems comprising perfluoromethyldecalin (PFMD) and non-fluorinated oils with different polarities was investigated. The measured interfacial tension between the pure liquids was quantitatively interpreted in the framework of the Fowkes' model. The interfacial activity of several kinds of non-fluorinated, perfluorinated, ionic and non-ionic surfactants was explored. The perfluorinated non-ionic compound perfluoroalkyi-polyoxyethylene (PFPE) proved to be most effective as a surfactant in these systems. The critical micelle concentration and the areas per molecule at interfaces with non-fluorinated oils were determined for this substance. In some cases where fluorinated alcohols were used as co-surfactants, ultra-low interfacial tension and microemulsion formation were observed. The stability of the emulsion using PFPE as a surfactant was also investigated. It was shown that the higher polarity of the non-fluorinated oils led to higher emulsion stability. The addition of fluorinated alcohols decreased the stability and reversed the macroemulsion type. The observed effects are discussed from the viewpoint of the chemical structure of the compounds.