The opposite of a bubble is an antibubble, a blob of liquid encased in a thin layer of air. Antibubbles usually pop a few minutes after they are made, but scientists have figured out how to make them last for 13 hours. Long-lasting antibubbles could be used for transporting chemicals or drugs in liquids.
Antibubbles were first observed in 1932, but they haven鈥檛 been widely used in practical devices or engineering processes because they are usually short-lived. Now, at the University of Liege in Belgium and his collaborators have used foam made of regular bubbles to boost the lifetime of antibubbles.
They placed a layer of conventional bubbles in a Plexiglas container. Next, they created antibubbles between the regular ones by adding droplets of a water and detergent mixture with a syringe. The antibubbles were trapped but still prone to popping quickly. However, when the team vibrated the mixture by shaking the whole container, the antibubbles lasted almost 400 times as long.
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鈥�13 hours is the maximum [lifetime] we observed, but compared to 120 seconds, to an antibubble this is like an infinity,鈥� Dorbolo says.
An antibubble pops because the air that forms its outer membrane starts to leak around the bottom, he says. As this part of the air membrane thins, the antibubble is reduced to a cap of air on top of a more and more rapidly swirling liquid before it finally disappears.
Shaking the antibubbles stopped the air membrane from breaking. A model of the system that Dorbolo devised showed that certain shaking frequencies and amplitudes extended antibubble lifetimes the most. These shaking protocols produced just the right amount of force and pressure to maintain air shells of even thickness.
In past experiments, other researchers have made long-lived antibubbles by adding special particles to the liquid they were made from 鈥� they armoured antibubbles with particles that prevented them from popping 鈥� but the new method directly counteracts the mechanics of antibubble death.
鈥淭his is an elegant way to stabilise antibubbles,鈥� says at Eindhoven University of Technology in the Netherlands. 鈥淚t could lead to new tools for [chemical] reaction engineering.鈥�
For instance, antibubbles containing a chemical required for a reaction could be added to a container with another chemical. Shaking the container would prevent the antibubbles from bursting until they are evenly mixed in, says Poortinga, at which point researchers could stop the shaking so that the antibubbles pop, jump-starting a reaction throughout the container. 鈥淪uch a homogeneous reaction is currently difficult to achieve and could lead to a much better control over the properties of the reaction,鈥� he says.
Dorbolo, however, says that such a practical application will require future work, like making the antibubbles smaller. Currently, he and his team are working with antibubbles one centimetre in size, while microscopic bubbles would be more useful for chemical engineering.
Reference: , in press
