Bubble coalescence, Foams and Thin Surfactant Films

Bubble Coalescence, Foams and Thin Surfactant Films 

Thin-liquid-film stability. The effect of surfactants on film and foam stability. Surface elasticity. Froth flotation. The Langmuir trough and monolayer deposition. Laboratory project on the flotation of powdered silica. 

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BUBBLE COALESCENCE, FOAMS AND THIN SURFACTANT FILMS... 

In pure liquids, gas bubbles will rise up and separate, more or less according to Stokes law. When two or more bubbles come together coalescence occurs very rapidly, without detectable flattening of the interface between them, i.e., there is no thin-film persistence. It is the adsorption of surfactant, at the gas-liquid interface, that promotes thin-film stability between the bubbles and lends a certain persistence to the foam structure. Here, when two bubbles of gas approach, the liquid film thins down to a persistent lamella instead of rupturing at the point of closest approach. In carefully controlled environments, it has been possible to make surfactant-stabilized, static, bubbles, and films with lifetimes on the order of months to years [45],... 

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