What’s the right mix of materials to blow big bubbles that stretch without popping? Physicists have turned up the solution.
Justin Burton’s fascination with soap bubbles began in Barcelona, Spain, six summers ago. “It was hot and humid, and there were guys on the street making these huge bubbles,” he says. “I thought it was the coolest thing.” When he returned home, his sister gave him a giant bubble wand. It included a recipe for a bubble-making solution. Burton began to blow. Now he’s improved the recipe and is ready to share it.
By the way, Burton is hardly your typical bubble-blower. As a physicist at Emory University in Atlanta, Ga., he studies forces in nature. Those forces include effects on fluids that flow. The more he thought about bubbles, the more he wanted to know just how they were made.
“What is it about bubble solutions that makes them [stretch] without ripping — and for such a long time?” he asks. Now, he’s found out. And he and his team reported the results of their scientific investigation on August 1 at arXiv.org.
Big bubbles exist at just the right balance of natural forces, they found. The bubble has to be stretchy, but not so much that it rips. And the wet soapy mixture has to flow evenly to form the bubble, resisting a tendency to pop. It also has to stay together, even as gravity pulls it down and some of the water evaporates.
Explainer: What are polymers?
In their new study, Burton and his coworkers identified the secret ingredient behind these traits: a polymer. It’s what holds the bubble together but lets it flow, too.
Polymers are long chains of identical molecules. In Burton’s case, he recommends one called guar. It’s made from natural fibers. Those fibers help form long-chain polymers when dissolved in water. That’s why guar is used as a thickener in many foods, including ice cream and puddings.
Adding polymers like guar to bubble recipes can produce colossal results. The official largest free-floating bubble was blown in 2015 in Cleveland, Ohio. It had a volume of 96.27 cubic meters (almost 3,400 cubic feet). That’s about the same volume as about 13,545 basketballs. It’s also about the size as a large classroom (although not in the same shape, of course.)
Perhaps most surprisingly, that record-setting bubble probably included only about 300 milliliters, or just over a cup, of bubble solution. Burton says that in such big bubbles, the soap film thins across the ballooning structure to just about one micrometer (also called a micron) thick. That’s a millionth of a meter (0.0004 inch).
“It’s just amazing that you can have a micron-thick film that extends to these dimensions,” Burton says.
