FYFD

Tag: science

  • Spreading By Island

    Spreading By Island

    How does a droplet sinking through an immiscible liquid settle onto a surface? Conventional wisdom suggests that the settling drop will slowly squeeze the ambient fluid film out of the way, form a liquid bridge to the solid beneath, and spread onto the surface. But for some droplets, that’s not how it goes.

    While watching a glycerol droplet settle through silicone oil, researchers discovered a new mechanism for wetting. Initially, the silicone oil drained from beneath the drop, as expected. But then the thinning of the film stalled. Tiny bright spots (above) appeared beneath the light and dark interference fringes of the parent drop. These are spots of glycerol, formed when material from the main drop dissolved into the oil and then nucleated onto the solid surface below. Over time, the island-like spots of glycerol grew. Eventually one grew large enough to coalesce with its parent drop (below), causing the glycerol to quickly spread over the solid surface!

    Islands nucleate and grow beneath a droplet until they're able to coalesce with the parent droplet above.
    Islands of liquid (darker rings) grow beneath a parent drop (brighter rings) until reaching a size where they coalesce, causing the interference fringes to disappear.

    The key to this phenomenon seems to be that immiscibility isn’t perfect. Even trace amounts of solubility between the drop and surrounding fluid are enough to allow these islands to form. And once formed, the islands will grow as long as the drop fluid and the solid surface are chemically attractive. (Image, research, and submission credit: S. Borkar and A. Ramachandran; see also Nature Behind the Paper)

  • Ice and Dunes

    Ice and Dunes

    Although dunes are usually associated with scorching climates, they can form in any desert, including in the frozen steppes of western Mongolia. This sunrise photo, taken by an astronaut aboard the ISS, shows Ulaagchinii Khar Nuur. The ice-covered Khar Nuur Lake surrounds two islands, Big and Small Avgash, and cold dunes form textured streaks on either side. The low sun angle accentuates the dunes, making every rippling crest clear. (Image credit: NASA; via NASA Earth Observatory)

  • Yosemite in Winter

    Yosemite in Winter

    Waterfalls, fog, and snow wreathe Yosemite in these beautiful winter landscapes by photographer Michael Shainblum. I love how the tendrils of water and mist give you a real sense of the flow, even in still photos. Check out more of Shainblum’s photography on his Instagram and go behind-the-scenes on his Yosemite trip with this video. (Image credit: M. Shainblum; via Colossal)

  • Falling Pancake Drops

    Falling Pancake Drops

    Despite their round appearance, the droplets you see here are actually shaped like little pancakes. They’re sandwiched inside a Hele-Shaw cell, essentially two plates with a viscous fluid between them. As these droplets fall through the cell, some remain steady and rounded (Image 1), while others experience instabilities (Images 2 and 3). By varying the ratio of the ambient fluid’s viscosity relative to the drop, the authors found two different kinds of breakup. In the first type (Image 2), droplet breakup occurred due to perturbations inside the drop itself. In the second type (Image 3), the viscosity of the ambient fluid is closer to that of the drop and intrusions of the ambient fluid into the drop break it apart. (Image and research credit: C. Toupoint et al.)

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    Ink-Based Propulsion

    In this video, Steve Mould explores an interesting phenomenon: propulsion via ballpoint pen ink. Placing ink on one side of a leaf or piece of paper turns it into a boat with a dramatic dye-filled wake. It’s not 100% clear what’s happening here, though I agree with Steve that there are likely several effects contributing.

    Firstly, there’s the Marangoni effect, the flow that happens from an area of low surface tension to high surface tension. This is what propels a soap boat as well as many water-walking insects. I think this is a big one here, and not just because the ink has surfactants. As any component of the ballpoint ink spreads, its varying concentration is going to trigger this effect.

    Secondly, there’s a rocket effect. Rockets operate on a fairly simple principle: throw mass out the back in order to go forward. These dye boats are also doing this to some extent.

    And finally there’s some chemistry going on. Some kind of reaction seems to be taking place between one or more of the ink components and the water in order to create the semi-solid layer of dye. Presumably this is why the dye doesn’t simply dissolve as it does in some of Steve’s other experiments.

    I figure some of my readers who are better versed in interfacial dynamics, rheology, and surface chemistry than I am will have some more insights. What do you think is going on here? (Video and image credit: S. Mould)

  • Swimming in Line

    Swimming in Line

    When swimming in open waters, it pays to keep your ducks (or your goslings!) in a row. A recent study examined the waves generated behind adult water fowl and found that babies following directly behind them benefit from their wake. In the right spot behind its mother, a duckling sees 158% less wave-drag than it would when swimming solo. That’s such a large reduction that the duckling actually gets pulled along! And the advantage doesn’t just help one duckling; a properly-placed duckling passes the benefit on to its siblings as well. So any duckling that stays in line has a much easier time keeping up, but those who slip out of the ideal spot will have a much tougher time. (Image credit: D. Spohr; research credit: Z. Yuan et al.; via Science News; submitted by Kam-Yung Soh)

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    Flying on Soap Films?

    YouTube channel Viral Video Lab has two videos showing 3D-printed gliders flying on wings formed from soap films. It’s a neat idea for a toy aircraft, though obviously not practical. But are the videos real? The channel features plenty of obviously fake concepts, like perpetual motion machines, and explicitly states in its About page that “videos shown on the channel may contain CGI effects.” They’re clearly not strangers to stretching the truth.

    Sadly, I don’t have the means to properly test the concept, but it at least seems plausible (although there are some flight sequences in the videos themselves that I don’t think are totally real). There are bubble solutions out there capable of making quite giant, long-lasting bubbles, though they are more complicated than the simple soap and water solution suggested in the video. And having essentially flat wings doesn’t preclude gliding, as long as you have a positive angle of attack. I’d be interested to see if someone with a 3D-printer can recreate the effect. Let me know if you give it a try! (Video credit: Viral Video Lab; via Gizmodo)

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    “Beyond the Horizon”

    Shifting bubbles and psychedelic colors abound in this abstract video from artist Rus Khasanov. He provides no specifics as to the materials he uses for this video, but my guess is they likely include oil, soap, and polarizing filters. It’s a fun and funky video! See more of Khasanov’s work on his website and Instagram. (Image and video credit: R. Khasanov)

  • Mountains in the Sky

    Mountains in the Sky

    Our skies can sometimes presage the weather to come. In thunderstorms, a cirrus plume above an anvil cloud will often appear (visible by satellite) about half an hour before severe conditions are reported on the ground. A new study delves into the origins of these plumes and finds that they result from an internal hydraulic jump in the storm that acts a bit like an artificial mountain, driving air — and the moisture it contains — higher in the stratosphere than normal. Once the jump is established, the authors found it could drive 7 tonnes per second of water vapor into the stratosphere! (Image credit: jplenio; research credit: M. O’Neill et al.; via Science)

  • Liquid Umbrellas

    Liquid Umbrellas

    Two well-timed and properly aligned droplets combine to create these umbrella-like fluid sculptures. The initial drop creates a jet that shoots upward. When the second drop hits that jet, it forms an expanding sheet of liquid like a miniature parasol. The higher the viscosity of the drops, the less lacy and unstable the sheet’s rim will be.

    Although set-ups for these sorts of pictures can be finicky, they’re very doable, even for amateur photographers. In fact, the techniques used here have been around for about a century! (Image and research credit: A. Kiyama et al.)