Modulation of the release from a w/o/w multiple emulsion by controlling the viscoelastic properties of the two interfaces

This paper describes the main results that we obtained in the study of two different lipophilic surfactants, Dow Corning Emulsifier 10 and Abil EM90, and the influence of their interfacial properties on the fragmentation and release from w/o/w multiple emulsions. Fluid w/o/w multiple emulsions were formulated with an original thermoresponsive polymer. The sol–gel transition at the application temperature of these two different preparations was investigated mainly by rheology. The emulsions were then sheared at 30 °C in order to simulate the release conditions that could be encountered during topical application. Although we obtained similar bulk rheological properties and fragmentation results for both multiple emulsions, the release rates after shear were very different, as we had disappointing results with Abil EM90. In order to explain this phenomenon, rheological properties of the interfacial films formed by the lipophilic surfactant alone, and by the lipophilic surfactant in combination with the thermogelling polymer, were determined and compared. Two release mechanisms were identified and found to be strongly correlated with the viscoelastic properties of the two interfaces.