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Relaxation in Aqueous Foams

Published online by Cambridge University Press:  29 November 2013

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Aqueous foams are macroscopically homogeneous complex fluids composed of co-existing gas and liquid phases. A hierarchy of structure and self-organization at progressively smaller length scales is ultimately responsible for the unique material properties of foams, and is shown schematically in Figure 1. A key feature of this microstructure is the continuous random network of liquid which typically occupies 1–10 vol% and separates the tightly packed gas bubbles. As shown by the photographs in Figure 2, the average bubble diameter can vary widely from about 10 μm to 1 cm, while the average bubble shape can vary from nearly spherical to nearly polyhedral, depending on the liquid volume fraction. At the smallest structural scale, surface active molecules are preferentially adsorbed at the gas/liquid interfaces and give rise to several physical-chemical effects that deter the coalescence of neighboring bubbles and thereby lend stability to the foam. However, the delicate structure formed by gas bubbles packed in a continuous liquid phase is not truly stable with either time or applied forces. This article reviews recent progress in understanding the structural response of aqueous foams to temporal and mechanical perturbations.

Type
Engineered Porous Materials
Copyright
Copyright © Materials Research Society 1994

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References

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