le 13 septembre 2019 à l'IPR, salle 6 du bâtiment 11A
Oil is often added to foam to destabilise it. In this case the oil acts as an antifoam promoting bubble coalescence. However, well-stabilised oil drops can be harmless to foam stability, and at high concentrations drops can considerably increase foam lifetimes. We encounter mixtures of oil drops and gas bubbles daily in food or cosmetic products, where they collectively give structure and texture to the materials. Despite the number of applications many questions remain on the properties of these multiphasic mixtures.
An image of such a foamed emulsion taken with a fluorescence microscope is shown below. We have explored the influence of oil in water emulsions on the stability and rheology of foams. Foamed emulsions destabilise in time as the oil, gas and water demix. We have followed the drainage of emulsions inside foam. Emulsions can slows down or even arrest drainage leading to very stable foams, before in some cases causing rapid foam collapse.
The addition of drops to bubbles gives increased opportunities to modulate the mechanical properties of the materials. We have explored the interaction between concentrated emulsions and bubbles and the rheological properties of the resulting materials. Our results can help create foamy materials with controlled stability and properties.