2. Stages in the life of a foam and associated phenomena

2.1 General conditions for obtaining foam

To form a foam, you first need to intimately mix a gas and a liquid; you also need a third component, because pure liquids don't foam, as the bubbles formed tend to break as soon as they come into contact with other bubbles or the free surface of the liquid.

The presence of a substance capable of stabilizing the films during the first moments of the foam's life is essential to allow the bubbles to accumulate to form the gas-liquid dispersion. These substances are generally surfactants. In this article, we will confine ourselves to these foaming agents, although it is known that molecular aggregates, polymers or solid nanoparticles can play a similar role, particularly for non-aqueous foams.