Scientists create 'antibubbles' in Belgian beer

Physicists from the University of Liège in Belgium have succeeded in creating antibubbles (the exact opposite of bubbles) in one of Belgium's most famous exports ­ beer.



Research to be published in the New Journal of Physics (NJP) shows for the first time how antibubbles form and move through a liquid. Antibubbles are the exact opposite of bubbles and move down instead of up. Whereas a bubble is a thin film of liquid in air and which encloses a pocket of air, an antibubble is a thin film of air made inside a liquid, enclosing a pocket of that liquid. Scientists have known about them for almost a century but why and how they form has been a mystery until now.

Dr Stéphane Dorbolo and colleagues at the University of Liège in Belgium and also at the Collège de France have proposed a mechanism which accurately describes how antibubbles are made and also how they move through a liquid. They observed antibubbles in a variety of liquids in the laboratory and made timed digital films of them; observing how they are created, how they move and also how they adie' when they burst. Antibubbles can be created by pouring a liquid containing a asurfactant' (eg the soapy water you wash dishes with) onto an identical liquid. They form because a thin film of air is sometimes pulled down along with the liquid itself. This air film then separates two liquids with the same composition and so is called an antibubble, since a real bubble is a liquid film separating two regions of air. This research appears online today in the New Journal of Physics, published jointly by the Institute of Physics and Deutsche Physikalische Gesellschaft (DPG).

Out of curiosity, the researchers also attempted to create antibubbles in Belgium's most famous export ­ beer. They did not think it would be possible because you cannot create antibubbles (or bubbles) in pure water, alcohol or oil.

However, they found that you can make antibubbles in beer. This is because beer contains protein which makes it a surfactant just like dishwashing liquid.

Dr Stéphane Dorbolo said: "Antibubbles are mysterious phenomena but we now understand them much better. We have come up with a good model describing how they form and move and have also learnt more about the type of liquids you can create them in. We tried to create them in beer for fun, and didn't think it would be possible, but were amazed when we managed to create giant antibubbles which lasted for almost two minutes and that moved around a glass of beer before bursting.“

He continued: "You can't create antibubbles in pure water, alcohol or oil. But beer is a special case because it is very similar to dishwashing liquid and contains what we call surfactants which is what you need to be able to produce antibubbles.“

www.iop.org or www.dpg-physik.de

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