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Search results for: “surface tension”

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    Mermaid Cereal

    In the Cheerios effect, floating objects can fall into one another due to capillary attraction — just like Cheerios link up in a cereal bowl. Here researchers play with that effect by adding repulsive magnets to their “cereal” pieces. They find that their so-called mermaid cereal falls into preferential spacing, with pieces pairing up but never touching. Adding lots of these pieces in a confined space creates interesting crystalline and striped patterns, as seen later in the video. (Video credit: A. Hooshanginejad et al.)

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    Magnetic Soap Films

    Soap films naturally thin over time as fluid evaporates and differences in film thickness cause surface-tension-driven flows. In this video, researchers experiment with adding magnetic nanoparticles to the soap film. In the second image, the white structures near the center of the film contain nanoparticles, and they’re drawn toward the magnet that sits (out-of-frame) to the left of the film. With more nanoparticles and a stronger magnetic field (Image 3), the entire soap film takes on a distinctive profile that thins from left to right. The effect is so strong that the film quickly thins to the point of rupture. (Image and video credit: N. Lalli et al.)

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    “Velocity”

    In this short film by Vadim Sherbakov, macro shots of glittery ink and pigments look like astronomical vistas. The title of the film, “Velocity,” is spot on; every shot is full of flow and motion driven by the mixture of ink, alcohol, soap, and other fluids. That means lots of surface-tension-driven flow, and the glitter particles act as excellent tracers, giving a real sense of depth and direction for our gaze to follow. Watching films like this, I always want to pull out some odds and ends and try it for myself, but I’m certain my results would pale in comparison! (Video and image credit: V. Sherbakov; via Colossal)

  • The Intermittent Spring of Afton, WY

    The Intermittent Spring of Afton, WY

    Yellowstone may get top billing, but Wyoming is home to more fluid dynamical wonders, like the world’s largest rhythmic spring. Located a little outside Afton, WY, Intermittent Spring — as the name indicates — runs for roughly 15 minutes, stops for the same length, then starts up again. The leading theory for this periodic flow depends on the siphon effect. Essentially, water runs continuously into a cavern underground, but to get to the surface, it must traverse a narrow tube with a high point that lies above the spring’s eventual exit. When the water level reaches that high point, it creates a siphon, sucking water out of the cavern and making the spring flow. But eventually the water level drops to the point where air rushes in, breaking off the flow until the water level recovers. That’s consistent with the spring’s behavior; it only runs in this intermittent fashion from late summer to fall, when groundwater levels are lower. (Image credit: Wikimedia Commons; video credit: University of Wyoming Extension; submitted by Kam-Yung Soh)

  • Listening to a Bubble’s Pop

    Listening to a Bubble’s Pop

    Sound is an important aspect of many flows, from the scream of a rocket engine to the hum of electrical wires vibrating in the wind. Critically, those sounds carry important information about the flow. A new study extends these acoustic diagnostics to the popping of soap bubbles.

    When a hole opens in a soap bubble, it throws the surface-tension-driven capillary forces of the bubble into disarray. The rim around the hole retracts, pushing fluid away from the expanding hole. At the same time, air is pushed out of the collapsing bubble. Using microphone arrays, the researchers found they could measure and distinguish sound from both sources — the escaping air and the expanding hole.

    From the sound, they developed a model that predicts the rupture location, bubble thickness profile, and other properties of the bubble. They confirmed the model’s results by comparing with high-speed photography. The authors hope their new acoustic technique will shed light on bubble bursting events that are hard to observe visually, like the bubbling of magma. (Image and research credit: A. Bussonnière et al.; via Science News; submitted by Kam-Yung Soh)

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    Paint Versus Hydrogel

    In this bizarre short film, we get to see a battle between dissolution and absorption. I think the Chemical Bouillon team has coated hydrogel beads in a layer of paint and then immersed them in water. As the beads absorb water, they expand and grow, tearing their fragile outer layer of paint to smithereens.

    One thing that struck me when watching several of the sequences is just how regular the hole spacing in the paint is for the round hydrogels. That hints at an orderly breakdown in the solid paint layer while the interior hydrogel polymer symmetrically expands. It’s a little like watching holes grow in a splash curtain. (Video and image credit: Chemical Bouillon)

  • Asymmetric Wakes

    Asymmetric Wakes

    When a ship moves through water, it leaves a distinctive V-shaped wake behind it. In the nineteenth century, Lord Kelvin made some of the earliest theoretical studies of this phenomenon, calculating that the arms of the V should have an angle of about 39 degrees, known as the Kelvin angle. But that theoretical result doesn’t always hold in practice.

    More recently, researchers calculated and experimentally verified an extension to Kelvin’s theory, one which accounts for what’s going on below the water. They found that any shear in the currents below the surface can strongly affect the shape of a boat’s wake, altering angles and creating asymmetry between the two sides. The results have practical consequences, too: they help predict the wave resistance ships will encounter when traversing areas with substantial subsurface shear, like near the mouths of river deltas. (Image credit: M. Adams; research credit: B. Smeltzer et al.; submitted by clogwog)

  • A Groovy Hovercraft

    A Groovy Hovercraft

    Not long ago, researchers discovered that droplets hovering over a hot grooved surface would self-propel. The extension to this was to investigate a hovercraft on a grooved, porous surface (top half of animation)–think an air hockey table with grooves. In that case, air inside the grooves flows from the point toward the edges, and it drags the hovercraft with it, thanks to viscosity. So the hovercraft travels in the direction opposite the points. This raised an obvious question: what happens if the hovercraft is grooved instead of the surface?

    That’s the situation we see in the bottom half of the animation. Air flows from the table and interacts with the grooves on the bottom of the hovercraft. And this time, the hovercraft propels in the direction of the points. That means there’s a completely different mechanism driving this levitation. When the grooves are onboard the hovercraft, pressure dominates over viscous effects. The air still gets directed down the grooves, but now, like a rocket, the exhaust pushes the hovercraft in the other direction – toward the points. For more on this work, check out the mathematical model of the problem and our interview with one of the researchers in the video below. (Research credit: H. de Maleprade et al.; image and video credit: N. Sharp and T. Crawford)

  • Building Liquid Circuits

    Building Liquid Circuits

    Building microfluidic circuits is generally a multi-day process, requiring a clean room and specialized manufacturing equipment. A new study suggests a quicker alternative using fluid walls to define the circuit instead of solid ones. The authors refer to their technique as “Freestyle Fluidics”. As seen above, the shape of the circuit is printed in the operating fluid, then covered by a layer of immiscible, transparent fluid. This outer layer help prevent evaporation. Underneath, the circuit holds its shape due to interfacial forces pinning it in place. Those same forces can be used to passively drive flow in the circuit, as shown in the lower animation, where fluid is pumped from one droplet to the other by pressure differences due to curvature. Changing the width of connecting channels can also direct flow in the circuits. This technique offers better biocompatibility than conventional microfluidic circuits, and the authors hope that this, along with simplified manufacturing, will help the technique spread. (Image and research credit: E. Walsh et al., source)

  • Wrapping Up

    Wrapping Up

    It’s often at the intersection of topics that we can learn something new and fascinating. The latest video from The Lutetium Project shows examples of this at the intersection of solid mechanics and fluid dynamics with a look at elastocapillarity. Breaking that word down, that’s where elasticity – that stretchy quality associated with solids – meets capillarity – the surface-tension-dominated behavior of a fluid. In particular, they explore some of the mind-boggling and surprising interactions that happen between drops, bubbles, and thin flexible fibers smaller than the width of a human hair. Check out the full video below. (Images credit: K. Dalnoki-Veress et al.; video credit: The Lutetium Project)

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