June 10, 2010
Scientists “˜Pop’ Bubble Mystery
Scientists reported on Wednesday that bubbles do not just disappear when they pop, but actually deflate in a rapid cascade of bubbles.
The physics behind this bursting effect seems to hold true whether the liquid is as thin as water or as thick as heavy oil, suggesting a universal theory of how bubbles behave when they break.
According to the study published in the British journal Nature, a host of practical applications could follow in areas ranging from health care to climate to glass manufacturing.
The study may also prove valuable for controlling processes in which bubble formation can be detrimental.
According to lead researcher James Brid, a graduate student at the Harvard School of Engineering and Applied Sciences, there was an element of serendipity in the discovery.
The team was working late one night investigating ways to spread bubbles on different surfaces when they noticed the rings that form when one bursts.
"After that, any time I was just walking around during a rainy day I'd look at the bubbles popping on puddles," Bird told AFP news.
"When I went swimming in the ocean I'd watch the bubbles on the surface... And I soon realized that it was everywhere."
He said in order to minimize surface area, a bubble forms an almost perfect hemisphere when it is in contact with a solid or liquid surface. When it pops, it creates a ring of smaller bubbles.
The entire process of this was not understood, until now.
In the first of the two-step process, the forces acting on the bubble cause the film to fold in on itself as it retracts, trapping a pocket of air in the shape of a donut.
He said that during the second stage, surface tension breaks this donut of air into a ring of smaller bubbles in the same way that surface tension transforms a thin stream of water flowing from a faucet into individual droplets.
The cascade effect is very short lived and could not be seen with the naked eye.
The team filmed the collapse with high-speed cameras and then used the video to construct a mathematical model to test and replicate their experimental hypothesis.
Bird said he was anxious to study similar popping effects in more exotics materials like molten glass, lava and mud.
"What I love about this study is that the overall effect can be seen by anyone in their kitchen," he said.
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