Criteria of Foam Stability

As it is known, if one blows air bubbles in pure water, no foam is formed. On the other hand, if a detergent or protein (amphiphile) is present in the system, adsorbed surfactant molecules at the interface give rise to foam or soap bubble formation. Foam can be characterized as a coarse dispersion of a gas in a liquid, where gas is the major phase volume. The foam, or the lamina of liquid, will tend to contract due to its surface tension, and a low surface tension would thus be expected to be a necessary requirement for a good foam-forming property. Furthermore, in order to be able 

Although the surface potential, g, the electrical potential due to the charge on the monolayers, will clearly affect the actual pressure required to thin the lamella to any given thickness, we shall assume for the purpose of a simple illustration that Mk, the mean Debye Huckel thickness of the ionic double layer, will influence the ultimate thickness when the liquid film is under a relatively low pressure. Let us also assume that each ionic atmosphere extends only to a distance 3/k into the liquid when the film is under a relatively low excess pressure from the gas in the bubbles this value corresponds to a repulsion potential of only a few millivolts. Thus at about 1 atm pressure. 

On the other hand, antifoam agents are not desirable in some of these systans, as for instance in food products. Further, antifoam agents deteriorate gas dispersion due to increased coalescence of bubbles. It has been long time that foams are stabilized by proteins, and that these are dependent on pH and electrolyte. 

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