Foamed emulsions with large volume fraction of the disperse phase

Foamed Emulsions with Large Volume Fraction of the Disperse Phase 

Foamed emulsions are disperse systems with two disperse phases (gas and liquid) in the disperse medium (surfactant solution). Water foamed emulsions are formed when foams or aqueous surfactant solutions are used to clean up oil deteriorated surfaces, in the process of oil flotation of waste waters, in firefighting when the foam contacts various organic liquids and in the processes of chemical defoaming (foam destruction by antifoams). Individual foamed emulsions can have practical importance e.g. a foamed emulsion of bitumen is used in road coating foamed emulsions from liquid fuels are used as explosives. 

In such concentrated disperse systems three types of liquid films form foam films (G/L/G), water-emulsion films (O/W/O) and non-symmetric films (O/W/G). The kinetics of thinning of these films, their permeability as well as the energy barrier impeding the film rupture determine the stability of these systems. They might be subjected to internal collapse, i.e. coalescence of bubbles or droplets and increase in their average size, or to destruction as a whole, i.e. separation into their initial phases - gas, oil and water. 

Since the densities of gas and oil are quite different, foamed emulsions can separate into concentrated emulsions and a polyhedral foam in which no oil (or very little) is present. The ability to control such instability proves to be the determining factor in the practical application of such systems. In that respect the only study known to the authors is [126]. 

It is known that the three film types are thermodynamically unstable. Long-living films can be obtained when suitable surfactants are employed, creating an energy barrier to film thinning, due either to the repulsion of the diffuse electric layers or the steric interaction of the adsorption surfactant layers. Since the minimum surfactant concentration that provides stable 

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