Foam breaking film rupture mechanisms

Schramm [257] considers it a big problem that foams are sensitive to the contact with oil under porous medium in oil recovery. While proposing a several foam breaking mechanisms under reservoir conditions, the author believes the emulsification process of oil in water is the most important step. In emulsification, the contact area of pseudo-emulsion films increases with the oil contents. In case the pseudo-emulsion films are stable, the foam stability and thus the process efficiency increases. Thinning of pseudo-emulsion films leads to its rupture when gas is continuously injected into the media, flooded with a surfactant solution at residual oil... 

Hydrophobic antifoams, the second group, attract surfactant from the foam bubbles and lead to film, rupture dispersion of hydrophobed silica particles in silicone oil is believed to occur following this mechanism [49]. Another hypothetical mechanism for a silicone defoamer is proposed by Dippenaar [50], Garrett [51], and Berg [52], in which the hydrophobic particles bridge the foam lamella, dewetting occurs at the surface of the particle, and, consequently, the foam breaks. 

Silicas are the most widely used active particles in defoamer formulations. Precipitated silicas are used almost exclusively. To be effective, the silica must be reacted with an agent, typically polydimethylsUoxane, to render the surface hydrophobic. The mechanism of bubble breaking is the dewetting of the silica particle by the foam lamella, which creates a defect in the film that leads to its rupture. The criterion for dewetting is a three-phase contact angle of 90° or more (the three phases are the aqueous foam lamella, the silica particle, and the carrier oil in which the particle is dispersed). Patterson has identified the properties of silica that optimize performance in... 

The mechanism oifilm rupture by nucleation of pores has been proposed by Deqaguin and Gutop (99) to explain the breaking of very fliin films, built up from two attached monolayers of amphiphilic molecules. Such are the secondary foam and emulsion films and the bilayer lipid membranes. This mechanism was further developed by Deijaguin and Prokhorov (3, 100, 101), Kashchiev and Exerowa(102—104), Chizmadzhev and coworkers (105— 107), and Kabalnov and Wennerstrom (108). The formation... 

In what follows we explain why particles are usually surface active at liquid interfaces. We also discuss mechanisms by which particles can rupture thin films in foams and emulsions. Because antifoam formulations are frequently dispersions of particle-containing oil droplets in an aqueous phase, we also allude to the way in which oil droplets can break foam films and to the synergy that exists between the oil and particles in this process. Finally, we illustrate some of our own work on the behavior of particle monolayers at (mainly) oil/water interfaces. Particularly important is the observation that very long range electrical repulsion between charge-bearing particles can occur through nonpolar oils at the oil/water interface. 

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