How is the bubble formed?

For bubbles, the basic structure is shown below, which is equivalent to a "surfactant-water-surfactant" sandwich, separating the air on both sides. Bubbles are in an unstable state in thermodynamics, and tend to become thinner, rupture and return to liquid state.

However, substances with surface activity are adsorbed on the gas-liquid interface of bubbles to form a single layer, which can prevent the local film from becoming too thin and breaking, but the whole film becomes evenly thin, so the bubbles will eventually break. This property is called film elasticity.

As one of the most traditional surfactants, soap has better foaming performance than most surfactants. Too much bubble is not necessarily a good thing. Too much foam is completely inelastic, giving people a loose feeling, and the amount of foam is not the only criterion for evaluating the quality of a facial cleanser.

Extended data:

Principle of foam cleaning:

First of all, bubbles appear because there are surfactants in these detergents, which are also the main substances that can be cleaned. Common surfactants are composed of two parts, one of which is hydrophilic (oleophobic) head group.

The other part is lipophilic (hydrophobic) carbon chain. When cleaning the surface, the lipophilic carbon chain is combined with grease, and then the hydrophilic head group is combined with water under the washing of water, and the stain is washed away. The basic principle is as shown above.

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