Time evolution of Foams made from Emulsions

2011 
Mixtures of foams and emulsions are found in many industrial products, where either they are purposefully created for reasons of function and texture or they are an unwanted side product due to the foaming of an emulsion during preparation or use. Interestingly, depending on the volume fractions of the components, type of surfactant and oil used emulsions can strongly increase the stability of foams or can act as anti-foams. Although some research has been conducted on emulsions as anti-foams[1], their use as stabilising agents for foaming has so far been much less explored[2]. In either case both the foam and the emulsion evolve with time, the bubble (drop) size increases and the fluids eventually phase separate. In mixtures the ageing of the emulsion will have an effect on the ageing of the foam and vice versa. We have studied a model foam-emulsion system using a single surfactant to stabilise both phases, thus changing from very unstable to long-lived foams. The time evolution of the systems has been followed using light scattering techniques, with particular emphasis on the highly stable foams. In such stable foams the emulsion droplets can get jammed inside the porous structure of the foam, thus making them interesting systems with which to study the effects of confinement on complex fluids.
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