Tiny bubbles break each other up

Rice University News & Media

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A video shot at more than 30,000 frames per second shows how bubbles generated in a microfluidic device “pinch” one another as they create a foam. Rice University engineers made the devices to generate foam with bubbles in two or three distinct sizes. Courtesy of the Biswal Lab

Rice University engineers demonstrate mechanics of making foam with bubbles in distinct sizes
HOUSTON – (Dec. 6, 2018) – It’s easy to make bubbles, but try making hundreds of thousands of them a minute – all the same size.
Rice University engineers can do that and much more. Rice chemical and biomolecular engineer Sibani Lisa Biswal and lead author and graduate student Daniel Vecchiolla have created a microfluidic device that pumps out more than 15,000 microscopic bubbles a second and can be tuned to make them in one, two or three distinct sizes.
A sequence shows the progression of bidisperse foam generation in a microfluidic device created at Rice University. When bubbles enter, they pinch the preceding bubble into two before becoming a wall against which the next bubble will be pinched. Courtesy of the Biswal Lab
The work featured on the cover of the Royal Society of Chemistry journal Soft Matter enables customizable, “wet” foams in small amounts for applications that include chemical and biological studies.
The best part is that the bubbles themselves do the hard part.
A movie that demonstrates the mechanism shows elongated bubbles shooting through a tube into an input channel. Each arrow-like bubble moves with enough force to split the bubble ahead of it, but the arrow remains intact. It takes its place between the new “daughter” bubbles and becomes a “wall” that holds the next bubble in place for splitting. In that way, only every other bubble entering the expansion splits from the inter-bubble forces.
A foam with bubbles in two distinct sizes is contained in a microfluidic device …

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