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Search results for: “droplet”

  • Shaped Splashes

    Shaped Splashes

    When a raindrop hits a leaf, it spreads out into a rimmed sheet that breaks up into droplets. These tiny drops can carry dust, spores, and even pathogens as they fly off. But many leaves aren’t smooth-edged; instead they have serrations or teeth. How does that affect a splash? That’s the question at the heart of today’s study.

    A water drop hits a star-shaped pillar and breaks up.
    A water drop hits a star-shaped pillar and breaks up.

    To simplify from a leaf’s shape, the team studied water dropping onto star-shaped pillars. As seen above and below, the pillar’s edge shaped the splash sheet, with the sheet extending further in the edge’s troughs. This asymmetry extends into the rim also, concentrating the liquid — and the subsequent spray of droplets — along lines that extend from the edge’s troughs and peaks.

    A viscous water-glycerol drop hits a star-shaped pillar, spreads, and breaks into droplets.
    A viscous water-glycerol drop hits a star-shaped pillar, spreads, and breaks into droplets.

    The team found that, in addition to sending drops along a preferred direction, the shaped edge made the droplets larger and faster than a smooth edge did. (Image and research credit: T. Bauer and T. Gilet)

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    “Starlit”

    In “Starlit,” filmmaker Roman de Giuli leverages paint, ink, water, and oil to create astronomical views. Colorful droplets spin past like neon exoplanets. Shards of glitter form comets. Satellite droplets become moons about their larger sibling. (Video and image credit: R. de Giuli)

  • Hole Punch Clouds

    Hole Punch Clouds

    At times altocumulus cloud cover is pierced by circular or elongated holes, filled only with the wispiest of virga. These odd holes are known by many names: cavum, fallstreak holes, and hole punch clouds. Long-running debates about these clouds’ origins were put to rest some 14 years ago, after scientists showed they were triggered by airplanes passing through layers of supercooled droplets.

    When supercooled, water droplets hang in the air without freezing, even though they are colder than the freezing point. This typically happens when the water is too pure to provide the specks of dust or biomass needed to form the nucleus of an ice crystal. But when an airplane passes through, the air accelerated over its wings gets even colder, dropping the temperature another 20 degrees Celsius. That is cold enough that, even without a nucleus, water drops will freeze. More and more ice crystals will form, until they grow heavy enough to fall, leaving behind a clear hole or wisps of falling precipitation.

    In the satellite image above, flights moving in and out of Miami International Airport have left a variety of holes in the cloud cover each of them large enough to see from space! (Image credit: M. Garrison; research credit: A. Heymsfield et al. 2010 and A. Heymsfield et al. 2011; via NASA Earth Observatory)

  • Making a Splash

    Making a Splash

    Since Harold Edgerton’s experiments with stroboscopic photographs in the 1930s, we’ve been fascinated by the shape of splashes. These days students and artists can take advantage of programmable external flashes to capture this split-second moment of impact. Here, a pink-dyed drop of ethanol strikes a jet rising from a pool of glycerin, milk, and food coloring. The resulting splash is umbrella-like, with a thickened rim that shows tiny ligaments of fluid — an early sign of the instability that will ultimately detach droplets from the splash. This image was taken by students in a course that connects art and fluid mechanics. (Image credit: L. Sharpe et al.; via Physics Today)

  • Making Reconfigurable Liquid Circuits

    Making Reconfigurable Liquid Circuits

    Microfluidic circuits are key to “labs on a chip” used in medical diagnostics, inkjet printing, and basic research. Typically, channels in these circuits are printed or etched onto solid surfaces, making it difficult to reconfigure them. A group in China developed an alternative design, inspired by reconfigurable toys like Lego blocks. Their set-up, shown above, uses a pillared surface immersed in oil. To create the channels, they pipette water — one droplet at a time — into the space between pillars. The combination of oil and pillars traps the drop. With multiple drops linked together, they get channels, like the ones above that mix two fluids. When the time comes to reconfigure the channels, they just pipette the water out and cut the channel with a sheet of coated paper. (Image and research credit: Y. Zeng et al.; via Physics Today)

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    Making Magnetic Crystals From Ferrofluids

    Ferrofluids are a great platform for exploring liquids and magnetism. Here, researchers trap ferrofluid droplets along an oil-water meniscus and then apply a magnetic field that makes the drops repel one another. The results are crystalline patterns formed from magnetic droplets. For a given patch of drops, increasing the magnetic field’s strength pushes drops further apart. But changing the drops’ size and levels of self-attraction also shifts the patterns. Check out the video to see the crystals in action. (Video and image credit: H. Khattak et al.)

  • Why Inkjet Paper Curls

    Why Inkjet Paper Curls

    Printed pages from inkjet printers tends to curl up over time. Researchers found that this long-term curl correlates with the migration of glycerol — one of the solvents used in inkjet ink — through the paper’s fiber layers toward the unprinted side. The glycerol migration makes the cellulose fibers in the paper swell up, causing the curl. Changing the solvent used in inkjet inks could stop the curl but would likely lead to printing issues, since the glycerol helps the tiny droplets wind up in the right place on the page. Another solution? Print on both sides of the page! (Image credit: Lunghammer – TU Graz; research credit: A. Maass and U. Hirn; via Physics World)

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    Sharpshooters

    The sharpshooter‘s superpower is pee flinging. These insects consume nutrient-poor plant sap, so to get the calories they need, they have to drink 300 times their body weight each day. All that extra liquid has to go somewhere, so the sharpshooter evolved to be an expert excretor. Each drop gathers on their anal stylus, then gets launched with an energy-efficient flick. During that move, the sharpshooter compresses the droplet, adding a little extra energy that helps speed up the drop’s flight once launched. (Video and image credit: Deep Look)

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    Serpents and Ouroboros

    Beads of condensation on a cooling, oil-slicked surface have a dance all their own in this video. Large droplets gobble up their fellows as they follow serpentine paths; each new droplet donates its interfacial energy to feed the larger drop’s kinetic energy. Eventually, the big drops switch to a circular path, like an ouroboros, the tail-eating serpent of mythology. This transition happens due to the oil shifted by the dancing droplets. You can recreate the effect at home by rubbing a thin layer of oil over glass and setting it atop a hot mug of your favorite beverage. (Video and image credit: M. Lin et al.; research credit: M. Lin et al.)

  • Skittering Drops

    Skittering Drops

    Drip some ethanol on a hot surface, and you’d expect it to spread into a thin layer and evaporate. But that doesn’t always happen, and a recent study looks at why.

    Ethanol is what’s known as a volatile liquid, meaning that it evaporates easily at room temperatures, well below its boiling point. When dropped on a uniformly heated surface above 45 degrees Celsius, the drop contracted into a hemisphere and then began to wander randomly across the surface. Researchers trained an infrared camera on the drop from below (above image), and found an unsteady, roiling motion inside the drop. These asymmetric flows, they concluded, drive the drop’s erratic self-propulsion. They suspect the mechanism may explain why some ink droplets wind up in the wrong place on a page during ink-jet printing. (Image and research credit: P. Kant et al.; via APS Physics)

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