Multiple Emulsions

Multiple emulsions are termed emulsions of emulsions, the droplets of the dispersed phase themselves containing even smaller dispersed droplets. More than seventy years ago, William Seifriz reported on the formation of multiple emulsions during an inversion of an O/W emulsion into a W/O emulsion. At present, the common terminology refers to two types of multiple emulsions: W/O/W emulsions, in which the external continuous phase is aqueous, or O/W/O emulsions, in which the external continuous phase is an oil. This chapter describes the various possibilities of preparing multiple emulsions and gives the reader the basic tools with which to form and evaluate the resulting multiple emulsions. It is possible to obtain multiple emulsions by inversion of either O/W to W/O emulsions or W/O to O/W emulsions by using an emulsifier with an hydrophil-lipophil balance value that does not particularly favor a certain type of emulsion, such as sorbitan monopalmitate.