Breakdown Processes of Multiple Emulsions

It should be noted that type A multiple emulsions are not encountered much in practice, while type C is difficult to prepare as a large number of small water internal droplets (which are produced in the primary emulsification process) results in a large increase in viscosity. Thus, the most common multiple emulsions used in practice are those represented by type B. 

Florence and Whitehill [1] identified several types of breakdown process. The external oil drops may coalesce with other oil drops (which may or may not contain internal aqueous droplets) alternatively, the internal aqueous droplets may be individually expelled, more than one may be expelled, or they may be less frequently expelled in one step. The internal droplets may coalesce before being 

All of the above processes are influenced by the nature of the two emulsifiers used to prepare the multiple emulsion. Most reports on multiple emulsions are based on conventional nonionic surfactants, but unfortunately most of these surfactant systems produce multiple emulsions with Hmited shelf-Uves, particularly if the system is subjected to large temperature variations. During the past few years, multiple emulsions have been formulated using polymeric surfactants for both the primary and multiple emulsion preparation. These polymeric surfactants proved to be superior over conventional nonionic surfactants in maintaining the physical stability of the multiple emulsion, such that today they may be applied successfully to the formulation of agrochemical multiple emulsions. The results obtained using these polymeric surfactants offer several potential applications in formulations. The key in the latter cases is to use polymeric surfactants that are approved by the FDA for pharmacy and food, by the CTA for cosmetics, and by the EPA for agrochemicals. 

One of the main instabihties of multiple emulsions is the osmotic flow of water from the internal to the external phase, or vice versa, which leads to shrinkage or sweUing of the internal water droplets, respectively. This process assumes the oil layer to act as a semi-permeable membrane (permeable to water, but not to solute). 

The volume flow of water, may be equated with the change of droplet volume 

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