Abstract and Keywords
This article focuses on foams, which consist of gas bubbles surrounded by liquid and closely packed together so that they are in contact with each other. As a mixture of two fluids, a foam is paradoxically a solid, at least under a small enough stress — surface tension and gas pressure maintain it in equilibrium when deformed. The corresponding mixture of two liquids is an emulsion, rendered stiff by surface tension under low stress. After explaining what a foam is, this article discusses various applications of foams. It then considers the statics and dynamics of foams, the simple rules that govern local equilibrium, and the structure of foams. It also examines the key properties of foams, such as coarsening due to diffusion, coalescence, drainage, foamability, rheology and rheometry, shear localization, conductivity, and light scattering. Finally, it describes the role of surfactants in foam stability and evaluates analogous systems such as emulsions.
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