Two new papers explore the complicated physics behind bubbles and foams


Enlarge / The complex physics of bubbles and foams have fascinated scientists for centuries. (credit: Ian Kington/AFP/Getty Images)

Human beings derive intense pleasure from bubbles and all kinds of foamy products, and scientists have long found them equally fascinating, given the complicated underlying physics. Most recently, a group of Japanese researchers published a paper in Scientific Reports describing two distinct mechanisms by which simple foams collapse. And in a new paper in the Proceedings of the National Academy of Sciences, physicists at MIT and Princeton University demonstrated how to develop spherical bubbles uniformly by confining them in a narrow tube.

Individual bubbles typically form a sphere, because that’s the shape with the minimum surface area for any volume and hence is the most energy efficient. Back in the 19th century, Lord Kelvin proposed a bizarre soccer-ball shape called a tetrakaidecahedron (Greek for “fourteen faces” and sometimes translated “tetradecahedron”), with six square and eight hexagonal faces, to describe a bubble’s natural geometry. It’s known as “Lord Kelvin’s cell,” and while it was a valiant effort, that exact structure has yet to be observed in real-world bubbles, although physicists from Trinity College Dublin proposed a better solution to the conundrum in a 1993 paper.

Foams are ubiquitous in everyday life, found in foods (whipped cream), beverages (beer, cappuccino), shaving cream and hair-styling mousse, packing peanuts, building insulation, flame-retardant materials, and so forth. All foams are the result of air being beaten into a liquid formula that contains some kind of surfactant (active surface agent), usually fats or proteins in edible foams, or chemical additives in non-edible products. That surfactant strengthens the liquid film walls of the bubbles to keep them from collapsing.

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