Double emulsions: formulations, scope and vehicular systems.

Multiple emulsions are complex and metastable systems. The droplets of the dispersed phasecontain even smaller dispersed droplets themselves.Each dispersed globule in the double emulsion forms avesicular structure with single or multiple aqueouscompartments separated from the aqueous phase by alayer of oil phase compartments. They could bepotentially applied to several usages so aspharmaceutical drug delivery, foods and cosmetics.W/O/W emulsions present many interestingpossibilities for the controlled release of drugs andcosmetics. They can entrap substances in the inneraqueous phase, protect them from degradation andmodulate their release rate to improve product efficacy. It has been shown that this release depends on variousmechanisms. The composition of the multipleemulsions is significant importance since the differentsurfactants, along with the nature and concentration ofthe oil phase, will affect thestability of the doubleemulsion. Several works has been done on the nature ofoils in relation to the selected emulsifiers and theirinfluence on the manufacturing conditions, as well ason the stability of the double emulsion. The emulsifiers have been found to migrate from one interface to theother and alter the interfacial emulsifier organization. It seems that the stability could be improved byincreasing the lipophilic surfactant concentration,which could strengthen the interfacial film.