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Search results for: “surface tension”

  • Predicting Droplet Sizes

    Predicting Droplet Sizes

    Squeeze a bottle of cleaning spray, and the nozzle transforms a liquid jet into a spray of droplets. These droplets come in many sizes, and predicting them is difficult because the droplets’ size distribution depends on the details of how their parent liquid broke up. Shown above is a simplified experimental version of this, beginning with a jet of air striking a spherical water droplet on the far left. In less than 3 milliseconds, the droplet has flattened into a pancake shape. In another 4 milliseconds, the pancake has ballooned into a shape called a bag, made up of a thin, curved water sheet surrounded by a thicker rim. A mere 10 milliseconds after the jet and drop first meet, the liquid is now a spray of smaller droplets.

    Researchers have found that the sizes of these final droplets depend on the balance between the airflow and the drop’s surface tension; these two factors determine how the drop breaks up, whether that’s rim first, bag first, or due to a collision between the bag and rim. (Image credit: I. Jackiw et al.; via APS Physics)

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    Marangoni Blossoms

    When surface tension varies along an interface, fluids move from regions of low surface tension to higher surface tension, a behavior known as the Marangoni effect. Here, a drop of (dyed) water is placed on glycerol. The two fluids are miscible, but water has much a lower viscosity and density yet a higher surface tension. The drop’s interface quickly becomes unstable; viscous fingers form along the edge as the less viscous water pushes into the more viscous glycerol. Eventually, the surface-tension-driven Marangoni flow breaks those fingers off into lip-like daughter drops. The researchers also show how the interplay between viscosity and surface tension affects the size of fingers that form by varying the water/glycerol concentration. (Image and video credit: A. Hooshanginejad et al.)

  • Bubblegum Sculptures

    Bubblegum Sculptures

    Like soap bubbles, bubbles blown in gum are ephemeral, lasting only seconds. Their break-up mechanism is quite different, though. Where surface tension rips a bubble apart once it is pierced, bubblegum instead deflates and wrinkles around a hole that does not grow, thanks to the elasticity of the gum. This photographic series by Suzanne Saroff features a rainbow of gum sculptures, all frozen in the moments of their disintegration. (Image credit: S. Saroff; via Colossal)

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    “Color Show”

    Brightly colored paints and inks mix and flow in artist Roman De Giuli’s “Color Show.” De Giuli typically creates this fluid art in thin layers atop paper. He’s a master of the form, manipulating surface tension gradients to create streaming flows, dendritic patterns, and feathery wisps. If this kind of art is your jam, he offers an app full of live wallpapers* for Android phones. See more of his work on his website and on Instagram. (Video and image credit: R. De Giuli)
    *Not sponsored, I just like his art!

  • Lasers and Soap Films

    Lasers and Soap Films

    Soap films are a great system for visualizing fluid flows. Researchers use them to look at flags, fish schooling and drafting, and even wind turbines. In this work, researchers explore the soap film’s reaction to lasers. When surfactant concentrations in the soap film are low, laser pulses create shock waves (above) in the film that resemble those seen in aerodynamics. The laser raises the temperature at its point of impact, lowering the local surface tension. That temperature difference triggers a Marangoni flow that draws the heated fluid outward. The low surfactant concentration gives the soap film relatively high elasticity, and that allows the shock waves to form.

    In contrast, a soap film with a high concentration of surfactants has relatively little elasticity. In these films (below), the laser creates a mark that stays visible on the flowing soap film. This “engraving” technique could be used to visualize flow in the soap film without using tracer particles. (Image and research credit: Y. Zhao and H. Xu)

    When surfactant concentrations are high, a laser pulse "engraves" spots onto a flowing soap film. Shown in terms of interference (left) and Schlieren (right) imaging.
    When surfactant concentrations are high, a laser pulse “engraves” spots onto a flowing soap film. Shown in terms of interference (left) and Schlieren (right) imaging.
  • Vortex Below

    Vortex Below

    When a drop of ethanol lands on a pool of water, surface tension forces draw it into a fast-spreading film. Evenly-spaced plumes form at the edges of the film, then the film stops spreading and instead retracts. All of this takes place in about 0.6 seconds. But, as the image above shows, there’s more that goes on beneath the surface. A vortex ring forms and spreads under the film, driven by the shear layer under the edge of the plumes. Here, the vortex ring is visible in the swirling particles near the water surface. (Image and research credit: A. Pant and B. Puthenveettil)

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    “Lucid”

    Artist Roman Hill made this official music video to go with Thomas Vanz’s “Lucid.” The imagery, formed from ink and other fluids, warps our sense of scale. Though the camera focuses on an extremely small area, to our eyes the results shift from nebulas to oceans and back again. There are likely a whole host of phenomena going on here, but without knowing more about Hill’s ingredients, I can only speculate that there are Marangoni flows driven by variations in surface tension and maybe some density instabilities going on between fluid layers. I’m also fairly confident that Hill has played with time reversal in the video editing. Regardless of the secrets in its making, the film is captivating and gorgeous. (Image and video credit: R. Hill)

  • Mocha Diffusion

    Mocha Diffusion

    These firework-like patterns spread when dyes are added atop a viscous but miscible lower fluid layer. Here, researchers use lower layers like corn syrup and xanthan gum; then they spread dye mixtures including ammonia and vinegar atop those layers. Because the upper and lower layers of fluid are miscible and can diffuse into one another, they together form elaborate patterns. The mixing of the two layers creates gradients in surface tension that can drive the flow and create these mocha diffusion patterns. (Image credit: T. Watson and J. Burton)

  • Water Jumping Hoops

    Water Jumping Hoops

    Small creatures like springtails and spiders can jump off the air-water interface using surface tension. But larger creatures can water-jump, too, using drag. Here, researchers study drag-based water jumping with a simple elastic hoop. Initially, two sides of the hoop are pulled closer by a string, deforming the hoop. Then, with the hoop sitting upright on the air-water interface, a laser burns the string, releasing the energy stored in the hoop. The hoop’s bottom pushes into the water, generating drag. That resistance provides a reaction force strong enough to launch the hoop.

    Compared to the hoop’s jumps off land, it’s slower to take-off from water, and it’s less efficient at jumping. Lighter hoops, however, jump better off water than heavier ones — a wrinkle that isn’t seen in ground jumpers. That suggests that weight reduction is more important for aquatic jumpers than for their terrestrial counterparts. (Image and research credit: H. Jeong et al.)

  • Frictional Fingers

    Frictional Fingers

    Air pushes into a thin gap filled with water and granular particles in the labyrinth-like image above. The encroaching air pushes grains like a bulldozer’s blade, building up a compacted wall. The invasion continues until the pressure of the air is countered by the combined capillary and frictional forces of the wet grains. Researchers built an analytical model that explains how these frictional fingers form and grow. Unlike Saffman-Taylor fingering patterns, which depend on long-range viscous forces, these patterns depend entirely on short-range forces from surface tension and friction. (Image and research credit: E. Flekkøy et al.)

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