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The secret lives of bubbles

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Movie of a collapsing soap bubble cluster, shown with thin-film interference and computed using a multiscale model of membrane rearrangement, drainage and rupture.
[Video courtesy of Saye & Sethian, UC Berkeley/LBNL]

A froth of soap suds, a handful of shaving cream or the mass of bubbles that sits on top of a freshly-poured soda—all of these things are foams or foam-like materials. They all have complex dynamics too, since the individual bubbles that make them up are constantly growing, popping and shape-shifting.

In the past, modeling the movements of foams has been very difficult because the clustering and bursting of bubbles, one-by-one, takes place in different places at different times. But, now, Robert Saye and James Sethian have broken down the various processes that allow foams to move around and evolve. The researchers then linked all of those processes back together in order to create a detailed model of foams, in general.

Saye and Sethian point out three separate phases of foam movement: the "rearrangement" of bubbles, the "drainage" of liquid through the bubbles and the eventual "bursting" of those bubbles. But, they also had to account for surface tension and gravity in their model.

Finally, the researchers tested their new foam formula on different-sized clusters of soap bubbles and proved that it does accurately predict the movement of such foamy materials.