Scientists Rethink How Bubbles Form

Bubbles add fizz to champagne and spring to foam mattresses, but the details about how they form have been murky.

A new computer simulation now challenges a theory about bubble formation that has been around since the 1920s and suggests they might form more simply, and faster, than was previously thought.

The finding, detailed online in the journal Physical Review Letters, could lead to a more precise understanding of the "phase transition" that takes place when bubbles form and could have implications for industries that rely on bubbles to make their products.

Bubbles and mountain passes

Scientists had thought bubbles form when jostling liquid molecules create pockets of low density in the liquid containing relatively fewer molecules than surrounding regions. Most of the time, other molecules will just rush in to fill in these air pockets. However, an exodus of molecules can also occur, causing the pockets, or bubbles, to grow.

David Corti, a chemical engineer at Purdue University in Indiana, compares the process to scaling a mountain. A pocket of air begins at the bottom of one side of the mountain (the liquid phase) and must climb the mountain and reach a destination on the other side (the vapor phase) to become a bubble.

"A small bubble needs to climb up one side of the mountain, cross through a reasonably well-defined mountain pass before it rolls down the other side of the mountain towards forming very large bubbles," Corti explained.

According to the conventional view, once the bubble makes it over the pass, it tumbles down the other side of the mountain like a snowball, picking up more molecules and growing bigger.

The new computer simulation suggests there "is no other side of the mountain," Corti told LiveScience. "Once it gets over the pass, we have found that the mountain just disappears, in a sense."

Rather than having to descend another slope, the bubble just plummets directly into the vapor phase. As a result, bubble formation might occur more rapidly than previously thought, Corti said.

Broader pathways

The new research also suggests the metaphorical mountain pass is actually more broad and flat than previously thought, allowing for several possible pathways from the liquid to the vapor phase.

"In the traditional view … there are only a few pathways that go through the pass," Corti said. "From our work, we have shown that it is in fact quite broad, so that there are a large number of pathways that will lead over the mountain top."

The findings could have implications for how scientists predict the rate of bubble formation, and could help improve safety for industries that rely on bubbles, the researchers say.

"We are still working out the full implications of this ourselves," Corti said.

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