FYFD

Tag: surface tension

  • Soap Film Filter

    Soap Film Filter

    Inspired by the self-healing properties of soap films, scientists have created a liquid filter capable of trapping small particles while allowing larger ones to pass through. Instead of filtering particles by size, as conventional filters do, this liquid membrane filters particles by kinetic energy; only large, fast-moving objects  pass through while slower and smaller ones get trapped. The membrane is a mixture of deionized water and sodium dodecyl sulfate, which allows researchers to finely tune the membrane’s surface tension and, therefore, how the filter behaves. Unlike soap films, the membrane is quite long-lived and robust. The team poked one for more than 3 hours without rupturing it.

    The researchers envision some pretty neat applications for these membranes, including a surgical membrane that would keep out dust and bacteria while doctors work or a membrane in a waterless toilet that could trap odors inside. (Image and research credit: B. Stogin et al.; video credit: Science; submitted by Kam-Yung Soh)

  • Coalescence

    Coalescence

    Simple acts like the coalescence of two droplets sitting on a surface can be beautiful and complex. As the droplets come together, they form a thin neck between them, and the curvature of that surface causes capillary forces that drive fluid into the neck. For two dissimilar droplets, like the ones above, there can be additional forces. Here, the upper drop is pure water, but the lower one has added surfactants, which reduce its surface tension. That difference in surface tension creates a Marangoni flow that tends to pull fluid away from the neck. The result is that full coalescence takes longer. Depending on other factors in this tug-of-war between capillary action and Marangoni flow, the process of coalescence can look very different. In this example, there’s a fingering instability that occurs as the neck spreads. Change the circumstances slightly and the drops may chase each other instead of merging or will merge with a perfectly smooth contact front. (Image and research credit: M. Bruning et al.)

  • Convection Without Heat

    Convection Without Heat

    We typically think of convection in terms of temperature differences, but the real driver is density. In the animations above, cream sitting atop a liqueur is undergoing solutal convection – no temperature difference needed! The alcohol in the liqueur mixes with the cream to form a lighter mixture that rises to the surface. The lower surface tension of the alcohol is also good at breaking up the cream, forming little cells. As the alcohol in those cells evaporates, the cream gets heavier and sinks down into the liqueur, where it can pick up more alcohol, rise back to the surface, and begin the cycle again. (Image credit: J. Monahan et al., source)

  • A Viscous Splash

    A Viscous Splash

    The splash of a drop may be commonplace, but it is still a mesmerizing and fertile phenomenon. When it comes to splashing, scientists are still learning how to predict the outcome. Here a drop of silicon oil impacts a film of silicon oil with an even higher viscosity. The momentum of that impact creates a crater and a splash curtain that rises and expands from the initial point of impact. Because the film viscosity is higher than the drop’s, the evolution of the corona slows down. Eventually, surface tension and gravity start pulling the splash curtain back down as the crater collapses. Meanwhile at the top of the splash, capillary forces pull fluid into the rim, which becomes unstable and grows cusps that eventually eject a cloud of smaller droplets. (Image and research credit: H. Kittel et al., source)

  • Spinning Droplet Galaxies

    Spinning Droplet Galaxies

    Water flung from a spinning tennis ball takes on a shape reminiscent of a spiral galaxy. As it detaches, water leaves the surface with both the tangential velocity of the spinning ball and a radial velocity due to the centrifugal force flinging it. The continued spin of the ball makes the thin ligaments of water still attached to it spiral and stretch. Eventually, surface tension can no longer hold the water together against the centrifugal forces, and the ligaments split into a spray of droplets. (Image credit: W. Derryberry and K. Tierney)

  • Featured Video Play Icon

    Bubble Art

    Everyone loves soap bubbles, and bubble artist Melody Yang reveals how to make some pretty awesome ones in this video for Wired. The surface tension of bubbles makes them naturally seek a shape that minimizes their surface area relative to the volume they contain. For a single bubble, that’s a sphere. But once you start joining multiple bubbles, as Yang demonstrates, that minimal surface area can change, even to something unexpected like a cube.

    Bubbles also have an impressive ability to self-heal. As long as whatever passes through them is wet – whether it’s a hand, a straw, or even a ball bearing – the soap film will probably heal itself rather than break. This is a key feature for many of Yang’s tricks, including the impressive planetary bubble. (Video credit: Wired; image credits: Wired/Colossal; via Colossal)

  • Featured Video Play Icon

    “Liquid Calligraphy”

    In “Liquid Calligraphy,” artist Rus Khasanov’s letters dissolve once he draws them. At first, the white ink spreads in narrow fingers, probably driven by a combination of surface tension gradients, capillary action, and simple diffusion. But then, in flashes, the letters morph faster and flow outward. My best guess is that each jump is a spray from a bottle full of a low surface tension liquid like alcohol. The spray triggers faster outflows than before, like those seen when a strong difference in surface tension activates the Marangoni effect. It’s a beautiful and different artistic take on these important fluid forces. Check out more of his videos here or enjoy high-resolution stills and wallpapers in this style from his Behance page. (Image and video credit: R. Khasanov; submitted by TBBQoC)

  • Rim Break-Up

    Rim Break-Up

    Splashing drops often expand into a liquid sheet and spray droplets from an unstable rim. Although this behavior is key to many natural and industrial processes, including disease transmission and printing, the physics of the rim formation and breakup has been difficult to unravel. But a new paper offers some exciting insight into this unsteady process. 

    The researchers found that if they carefully tracked the instantaneous, local acceleration and thickness of the rim, it always maintained a perfect balance between acceleration-induced forces and surface tension. That means that even though different points on the rim appear very different, there’s a universality to how they behave. They found that this rule held over a remarkably large range of situations, including across fluids of different viscosities and splashes on various surfaces. (Image and research credit: Y. Wang et al.; via MIT News; submitted by Kam-Yung Soh)

  • Fractal Fingers

    Fractal Fingers

    Dyed isopropyl alcohol atop a thin layer of acrylic medium spreads in a fractal fingering pattern. Although the shapes are reminiscent of the viscous fingers seen in in the Saffman-Taylor instability, these patterns are most likely a result of surface tension. The lower surface tension of the alcohol causes Marangoni forces to pull it outward. The branching shapes indicate an instability, likely driven by surface tension, but the details of the mechanism behind it are unclear. (Image credits: J. Nahabetian)

  • The Disintegrating Splash

    The Disintegrating Splash

    A drop of blue-dyed glycerine impacts a thin film of isopropanol, creating a spectacular splash and breakup. The drop’s impact flings a layer of the isopropanol into the air, where air currents make the thin sheet buckle inward and break into a spray of droplets. Meanwhile, the liquid from the drop forms a thick, blue crown that rises and expands outward. When tiny droplets of the isopropanol hit the splash crown, their lower surface tension causes the blue glycerine to pull away, due to the Marangoni effect. This opens up holes in the crown, which grow quickly, until the entire sheet breaks apart. (Image and research credit: A. Aljedaani et al., source)