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These High-Speed Snapshots of Water Droplets Are Nature's Kaleidoscope

Oh, and a breakthrough for scientific research.
Photos via Cornell

If you could take a snapshot of a drop of water in motion after it splashes onto a surface, and deconstruct it into a series of intricate geometric patterns, the effect would be quite remarkable—like peering into a kaleidoscope.

How do we know? Because scientists at Cornell University have done just that. Researchers used a high-speed camera to capture images of 37 different forms a droplet can take.

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The high-speed imaging makes it possible to see drops in motion in a way that wasn’t viewable before, so scientists can better understand and predict their behavior.

Researchers created an imaging platform called Omniview that has multiple mirrors to capture simultaneous top, left, and right views of a drop in motion. By changing up the nature of the drop—the density of the fluid, the angle of contact, the surface tension, or the speed of the drip—scientists looked at a variety of frequencies, each producing a different shape and size image.

You can compare it to a violin string, lead researcher Susan Daniel explained in an email. When it’s plucked, the frequencies are heard as sounds and harmonics. Different kinds of plucks make different frequencies, which create different sounds. Now imagine if you could deconstruct that vibrating motion into a snapshot photo. That’s what researchers are doing with oscillating droplets, but instead of “sound,” the photographs capture the harmonics of the motion of the drop, and the different frequencies correspond to deformed shapes and sizes.

“One can hear the beauty of music without knowing about notes, harmonics or scales, much like one can see the beauty of drop motions without knowing about the fundamental modes and their frequencies,” wrote Daniel. “On the other hand, one can now ‘make music with drops,’ designing new and better processes and deconstructing observations that we make.”

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The Omniview imager works as such: Light is shone through a metal mesh with tiny holes that’s affixed under the clear glass surface. As the light is refracted by the surface of the droplet, it’s seen as a deformation of the mesh, creating a visualization of the unique patterns of troughs and peaks that are captured on camera.

The result is a series of striking images. Researchers compiled the photos into an album, organized like a table of characteristics, arranged to make it easier for the human eye to properly identify the modes, shapes and patterns.

Being able to peer inside the chemistry of something as simple as a drop of water is cool, and useful too. For one, NASA, one of the supporters of the study, is interested in understanding how droplets on surfaces move in low gravity. To develop things like life support machines and heat exchangers for space travel, scientists have to understand the way liquid drops interact with gases in a zero or low-gravity environment.

The new research could also help improve high-resolution printing, since the way an ink droplet spreads when it touches a surface influences the image resolution. “When the drop is jetted onto the surface, essentially smacks into it, it oscillates and can spread and retract during this oscillation. So understanding the interplay of the drop dynamics and surface interactions are incredibly important for creating the most high resolution images possible,” Daniel said. The study will be published in Physical Review E on August 9.

Scientists have had fun with droplets before. Last month physicists at Aalto University and Paris Tech studied water droplets containing magnetic nanoparticles, that seemed to "dance" when placed on a superhydrophobic surface. When magnetized, the droplets divided and morphed into various structures and geometric patterns. When the magnet was taken away, they went back to the original form.

“I think high speed imaging has also allowed us to learn a lot about biological processes and materials,” said Daniel. “By being able to record and slow down the video later, one can see and study various changes, deformations, responses that give new insight into nature and man-made materials.” Physics never looked so good.