FYFD

Tag: viscoelasticity

  • Snails Tune Their Slime

    Snails Tune Their Slime

    Snails have a mucus for every occasion. The grove snail/lemon snail makes five different varieties: one for lubricating its motion, one for adhering to surfaces, one to seal it in its shell for winter, and two to protect against predators. A new study looks at how those different types of mucus differ.

    The basic building blocks of a snail’s mucus don’t vary much. It’s mostly water, spiked with proteins and carbohydrates that give it its complex properties. For the grove snail, collogen VI acts as the main structural component and amorphous calcium carbonate gets added in varying amounts during secretion. By tuning the amount of protein and added calcium, the snails tweak their mucus’ viscoelasticity for each purpose. (Image credit: Max Planck Institute of Colloids and Interfaces; research credit: M. Gabler et al.; via Ars Technica)

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  • Viscoelastic Vortex Street

    Viscoelastic Vortex Street

    When flow moves past a cylinder, vortices get shed in its wake. Known as a von Karman vortex street, this distinctive pattern is seen behind flags, islands, and even behind starships. Here, researchers are simulating flow of a viscoelastic fluid, where–unlike water or other Newtonian fluids–elastic stresses can build up.

    As the flow hits the leading edge of the cylinder, the polymers in the fluid compress and then get stretched as the flow moves around the cylinder. The left image shows vorticity in the flow; the right shows elastic stresses. The large swirls are primary vortices–those shed off the cylinder. But look closely and you’ll see smaller secondary vortices curled up beside the primaries. These form when the elastic stresses in the fluid pull some of the shear layer into the wake. (Image and research credit: U. Patel et al.)

    Simulation of a flow around a cylinder in a viscoelastic flow. Left, vorticity; right, elastic stresses.
  • Turbulence-Suppressing Polymers

    Turbulence-Suppressing Polymers

    Adding just a little polymer to a pipe flow speeds it up by reducing drag near the wall. But the effects on turbulence away from the wall have been harder to suss out. A new experiment shows that added polymers suppress eddy formation in the flow and reduce how much energy is lost to friction and, ultimately, heat. In particular, the researchers found that polymer stress helped stabilize shear layers in the flow and prevent them from destabilizing into more turbulent flow. (Image credit: S. Wilkinson; research credit: Y. Zhang et al.; via APS)

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  • Watch Hagfish Slime Unfurl

    Watch Hagfish Slime Unfurl

    The eel-like hagfish has one of the best defenses in the ocean. When threatened, it releases a slime that clogs the gills of its predator but allows the hagfish itself to slough off the slime and escape. The hagfish slime’s secret weapon is long protein threads, which are initially rolled into bundles called skeins. Seen above, these skeins resemble the yarn skeins knitters and crocheters buy, but a hagfish’s skeins are only as big as the width of a human hair.

    When water flows by quickly enough, the thread in a skein begins to unwind and stretch out. With enough threads unwound, the slime gets stretchy and viscous. Researchers found that it takes relatively little flow to begin this unwinding because the adhesion between threads and the surrounding fluid is higher than the thread-to-thread sticking power. (Research and image credit: M. Hossain et al., video)

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  • Tides Widen Ice Cracks

    Tides Widen Ice Cracks

    When icebergs calve off of Arctic and Antarctic coastlines, it affects glacial flows upstream as well as local mixing between fresh- and seawater. A recent study points to ocean tides as a major factor in widening the ice cracks that lead to calving. The team built a simplified mathematical model of an ice shelf, taking into account the ice’s viscoelasticity, local tides, and winds. Then they compared the model’s predictions with satellite, GPS, and radar data of Antarctica’s Brunt Ice Shelf, where an iceberg the size of Greater London broke off in 2023.

    Between their model and the observation data, the team was able to show that the crack that preceded calving consistently grew during the spring tides, when tidal forces were at their strongest. The work gives us one more clue for refining our predictions of when major calving events are likely. (Image and research credit: O. Marsh et al.; via Gizmodo)

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    “Droplet on a Plucked Wire”

    What happens to a droplet hanging on a wire when the wire gets plucked? That’s the fundamental question behind this video, which shows the effects of wire speed, viscosity, and viscoelasticity on a drop’s detachment. With lovely high-speed video and close-up views, you get to appreciate even subtle differences between each drop. Capillary waves, viscoelastic waves, and Plateau-Rayleigh instabilities abound! (Video and image credit: D. Maity et al.)

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  • Dripping Viscoelastics

    Dripping Viscoelastics

    An ultrasoft viscoelastic fluid drips in this research poster from the Gallery of Soft Matter. Complex materials like this one have stretchy, elastic behaviors typical of a solid along with the flowing, viscous properties of a fluid. Here, gravity overcomes the material’s elasticity, leaving it to sag and flow. As that happens, the fluid must slide past air, and the density difference between the two fluids creates the small distortions seen on the liquid sheet. This is an example of a Rayleigh-Taylor instability. (Image credit: J. Hwang et al.)

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    Building In a Stingless Hive

    Honeybees, with their stingers, get lots of attention, but the Americas have plenty of stinger-less honeymakers, too. These stingless bees are native to Mexico, where beekeepers cultivate them for pollination. Without stingers and venom, the bees use their building prowess to keep out unwanted visitors. Much of the hive — from the entrance’s nightly gate to the pods where young are stored — is built from cerumen, a substance the bees create by mixing wax with resins they collect from nearby trees. Just as they do with pollen, worker bees collect drops of resin and store them on their hind legs before flying back to the hive. The viscous fluid sticks well, until a swipe of a leg shears it enough to lower its viscosity and slide it off. (Video and image credit: Deep Look)

  • Viscoelasticity and Bubbles

    Viscoelasticity and Bubbles

    Bursting bubbles enhance our drinks, seed our clouds, and affect our health. Because these bubbles are so small, they’re easily affected by changes at the interface, like surfactants, Marangoni effects, or, as a recent study shows, viscoelasticity.

    A bubble released in pure water pops at the surface, creating a rebounding jet and a daughter droplet.
    A bubble released in pure water pops at the surface, creating a rebounding jet and a daughter droplet.

    In clean water, a bubble’s burst generates a rebounding jet that shoots off one or more daughter droplets, as seen in the animation above. But when researchers added proteins that modify only the water’s surface, they found something very different. As seen below, the bursting bubble no longer generated a jet, and, instead of forming droplets, it made a single, tiny daughter bubble. The difference, they found, comes from the added viscoelasticity of the surface. The long protein molecules resist getting stretched, which damps out the tiny waves that surface tension usually produces on the collapsing bubble cavity. (Image and research credit: B. Ji et al.; submission by Jie F.)

    When the surface of water is viscoelastic, a bursting bubble creates no jet and a daughter bubble instead of a drop.
    When the surface of water is viscoelastic, a bursting bubble creates no jet and a daughter bubble instead of a drop.
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    Fishing With Mucus

    The scaled wormsnail isn’t much for travel. It lives its whole life cemented to a rock in the tidal lands. And when you can’t go out for food, you have to wait for the food to come to you. During high tides, the snail lets out tendrils of mucus that capture bits of kelp, plankton, and whatever else the water brings. The snails haul their catch directly into their mouths, relying on the mucus’s impressive viscoelasticity to withstand the journey. (Video and image credit: Deep Look)