ABSTRACT
This chapter discusses different types of physical instability of pharmaceutical emulsions. It describes the strategies that may be utilized to stabilize emulsions. The surface-free energy of an emulsion is evident as the interfacial tension between the two phases. Addition of a surfactant to an emulsion leads to preferential translocation of the surfactant molecules to the interface of the two liquid phases since a surfactant is amphiphilic and molecules in both phases form attractive interactions with the surfactant molecule. An optimum amount of mixing shear and time are determined based on the rate of change of the size distribution of the dispersed phase with mixing. The resulting emulsion can then be packaged and/or dispensed. Multiple emulsions are emulsions whose dispersed phase contains droplets of another emulsion. Both water-in-oil-in-water (w/o/w) and oil-in-water-in-oil (o/w/o) multiple emulsions are of interest as delayed- and/or sustained-action drug delivery systems.
