FYFD

Tag: marangoni effect

  • Featured Video Play Icon

    When Bubbles Don’t Die

    In a pure liquid, most bubbles pop almost immediately. But with a simple ingredient — a little heat — bubbles can live almost indefinitely. The mechanism is revealed in this video when the researchers use an infrared camera to watch a bubble on a heated pool. The top of the bubble is cooler than the rest of the liquid, forming colder, denser droplets that slide down. But the cooler liquid also has a higher surface tension, which draws warm liquid up the bubble, replenishing it. The result is a stable bubble that simply carries on. (Image and video credit: S. Nath et al.)

  • “Delusion”

    “Delusion”

    Soap films are ephemeral and ever-changing. The shifting concentration of surfactants along the surface of the film, combined with thermally-driven convection, keeps the fluid in motion. The shifting colors reflect subtle changes in the soap film’s thickness. Over time, gravity drains fluid from the top of the film, thinning it to the point that it appears black. This photo from Bruno Militelli captures all of that detail in a striking and fascinating image that earned him 2nd place in the Manmade category of the Close-Up Photographer of the Year awards. You can find more winners of the competition here, and more of Militelli’s work on his website and Instagram. (Image credit: B. Militelli)

  • Featured Video Play Icon

    Acrylic Paint Fractals

    Here’s a simple fluids experiment you can try at home using acrylic paints, ink, isopropyl alcohol and a few other ingredients. When dropped onto diluted acrylic paint, a mixture of black ink and alcohol spreads in a fractal fingering pattern. The radial (outward) flow is driven by the alcohol’s evaporation, which increases the local surface tension and draws fluid outward. The shape and density of the fingers depends, at least in part, on the viscosity of the underlying paint layer; more viscous paint layers grow smaller and denser fractal patterns. (Image and video credit: S. Chan et al.)

  • Featured Video Play Icon

    “Halo”

    Fluids create mesmerizing practical effects in this new experimental film from the Julia Set Lab. I love how the visuals mess with your sense of scale. Some of the sequences look like they could be a solar firestorm or disintegrating sea ice, though in reality the camera’s field of view is probably smaller than your palm. The filmmakers provide no information on the fluids they use, but I spy some hints of partially miscible ingredients, some chemical reactions, and plenty of Marangoni action. (Video and submission credit: S. Bocci/Julia Set Lab)

  • Featured Video Play Icon

    The Yarning Droplet

    Marangoni bursting takes place in alcohol-water droplets; as the alcohol evaporates, surface tension changes across the liquid surface, generating a flow that tears the original drop into smaller droplets. Here researchers add a twist to the experiment using PMMA, an additive that dissolves well in alcohol but poorly in water. As the alcohol evaporates, the PMMA precipitates back out of the water-rich droplet, forming yarn-like strands. (Image and video credit: C. Seyfert and A. Marin)

  • Featured Video Play Icon

    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)

  • Featured Video Play Icon

    “Heterochromia Iridum”

    Heterochromia iridum is the formal name for when a person’s irises are multi-colored, often with streaks or swirls of one color cutting through another. In this short film, photographer Rus Khasanov recreates the effect with glittery inks and paints. Their varying surface tensions help create the eye-like streaks and feathers through the Marangoni effect. Check out the full video to see the effect in action. (Image and video credit: R. Khasanov; via Colossal)

  • Taking A Turn

    Taking A Turn

    Water droplets immersed in a mixture of oil and surfactants will move about, propelled by the Marangoni effect. Surfactant molecules congregate along the interface between the water and oil, but they do not do so uniformly. This uneven grouping causes variations in the surface tension, which in turn creates flows inside the droplet from areas of low surface tension to ones with higher surface tension. Those internal flows then dictate how the droplet as a whole moves.

    Researchers found that droplet trajectories in these systems depend on the droplet’s size. Small droplets move in relatively straight lines, whereas larger droplets take highly curved paths. The difference comes from the way surfactants get distributed around the drop’s interface. Larger drops are more sensitive to shifts in surfactant location, making them more prone to take changeable, curving paths. (Image credits: top – P. Godfrey, others – S. Suda et al.; research credit: S. Suda et al.; via APS Physics)

  • Featured Video Play Icon

    “Radiolarians”

    “Radiolarians” is a short film by artist Roman De Giuli using ink, alcohol, and oil. Much of the fluid motion involves break-up into droplets. The effects appear to rely heavily on Marangoni bursting, the physics of which you can learn about in this previous post. (Image and video credit: R. De Giuli)

  • “Liquid Skies”

    “Liquid Skies”

    “Liquid Skies” by Roman De Giuli is full of colorful but nebulous fluid imagery. The visuals consist of liquids like paint, ink, and alcohol filmed in macro atop paper. You can catch a behind-the-scenes glimpse of De Giuli at work here. (Image and video credit: R. De Giuli)