Physicists burst bubble mystery

By Victoria Gill
Science reporter, BBC News


With the help of high speed video, scientists have discovered that there is far more to bursting bubbles than meets the eye.

Under the right conditions, a bursting bubble on a liquid surface does not simply vanish, but creates a perfect ring of tiny "daughter bubbles".

This occurs as the ruptured bubble retracts into the liquid, forming a doughnut shape of trapped air.

image captionYou may see a ring of "daughter bubbles" while washing up

The scientists reported their discovery in the journal Nature.

In the paper, the team described a "bubble-bursting cascade".

"When one of these daughter bubbles ruptures, a ring of even smaller bubbles forms," the researchers wrote.

Eventually, the daughter bubbles are sufficiently tiny that they rupture to form sharp "jets" that propel small aerosol droplets into the atmosphere.

James Bird from Harvard University, who led the research, explained that his main interest was in the fundamental physics of how bubbles behave. But his discovery could eventually help to fine-tune many manufacturing processes.

"Where small bubbles are detrimental, such as in glass manufacturing, our results provide insight into how the parameters might be tuned to reduce the daughter bubbles," Dr Bird explained.

'Pop science'

He said that he happened upon the popping phenomenon accidentally while "playing around in the lab late one night".

"My colleague Laurent and I were trying to see if bubbles behaved like drops when they contacted a surface," he told BBC News.

"Our intended goal failed completely, but instead we were staring at popping hemispherical soap bubbles [and] we noticed this ring of daughter bubbles that neither of us could explain."

image captionHigh speed footage captured the bursting "cascade"

The scientists pointed that the finding could even have implications for health research - aerosol droplets from bursting bubbles have been implicated in the transmission of diseases in swimming pools and hot tubs.

They are also thought to be involved in the exchange of material and heat between the ocean and the atmosphere, so these results could help shed light on those processes.

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