Foam breaking stability

In the case where foam instability is desirable, it is essential to choose surfactants that weaken the Gibbs-Marangoni effect. A more surface-active material such as a poly(alkyl) siloxane is added to destabilize the foam. The siloxane surfactant adsorbs preferentially at the air/liquid interface, thus displacing the original surfactant that stabilizes the foam. In many cases, the siloxane surfactant is produced as an emulsion which also contains hydrophobic silica particles. This combination produces a synergetic effect for foam breaking. 

It is necessary to bear in mind that although Eqs. (4.9) and (4.10) are rigorously fulfilled at any hydrostatically equilibrium state of the foam, the capillary pressure exerts a strong influence on the drainage and foam stability. At a certain value of the capillary pressure, depending of foam dispersity and the foam film type, the foam lifetime becomes very short and the foam breaks down instantaneously. 

The soapy foam in which bubbles are stabilized by surface-adsorbed components. These foams cover a wide range of system factors. Sometimes chemical foam-breaking additives are used. 

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... 

Phenomena at Liquid Interfaces. The area of contact between two phases is called the interface three phases can have only aline of contact, and only a point of mutual contact is possible between four or more phases. Combinations of phases encountered in surfactant systems are L—G, L—L—G, L—S—G, L—S—S—G, L—L, L—L—L, L—S—S, L—L—S—S—G, L—S, L—L—S, and L—L—S—G, where G = gas, L = liquid, and S = solid. An example of an L—L—S—G system is an aqueous surfactant solution containing an emulsified oil, suspended soHd, and entrained air (see Emulsions Foams). This embodies several conditions common to practical surfactant systems. First, because the surface area of a phase iacreases as particle size decreases, the emulsion, suspension, and entrained gas each have large areas of contact with the surfactant solution. Next, because iaterfaces can only exist between two phases, analysis of phenomena ia the L—L—S—G system breaks down iato a series of analyses, ie, surfactant solution to the emulsion, soHd, and gas. It is also apparent that the surfactant must be stabilizing the system by preventing contact between the emulsified oil and dispersed soHd. FiaaHy, the dispersed phases are ia equiUbrium with each other through their common equiUbrium with the surfactant solution. 

Since we want the texture of products like shaving cream to stay stable, and since shampoo advertisers like to pretend that unnecessary extra lather is an important selling point, foam stabilizers are helpful in preventing foams from breaking down. 

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