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  • Mixing the Immiscible

    Mixing the Immiscible

    Immiscible liquids — like oil and water — do not combine easily. Typically, with enough effort, you can create an emulsion — a mixture formed from droplets of one liquid suspended in the other — like the one above. But a team of researchers have taken mixing immiscible liquids to a new level using their Vortex Fluid Device (VFD).

    Longtime readers may remember the group from their Ig-Nobel-winning demonstration of unboiling an egg, but this time the team is used the VFD to mix and de-mix immiscible liquids. As shown in the video below, the VFD is essentially a fast-spinning tube tilted at a 45-degree angle. As it spins, the liquids inside are forced into thin films with very high shear rates — high enough that immiscible liquids like water and toluene are forced together without forming an emulsion. Essentially, the mechanical forces mixing the liquids are strong enough to overcome the chemistry that typically keeps them apart.

    Impressively, the device manages this without using harsh surfactants or catalysts that other methods rely on. As a result, the technique offers a greener method for mixing chemicals for pharmaceuticals, cosmetics, food processing, and more. (Image credit: pisauikan; research credit: M. Jellicoe et al.; video credit: Flinders University; submitted by Marc A.)

  • Sunrise Cloudscape

    Sunrise Cloudscape

    With the low sun angle of dawn, the details of this cloudscape stand out. Captured by an external camera on the International Space Station, this image shows cloud formations over the northwest Atlantic. In the foreground, towering cumuli mark rising plumes of warm, moist air evaporating from the ocean. Beyond those clouds, a flat anvil cloud spreads horizontally after a temperature inversion prevented it from rising any further. (Image credit: NASA; via NASA Earth Observatory)

  • Coronal Heating

    Coronal Heating

    Compared to its interior, the surface of our sun is a cool 6,000 degrees Celsius. But beyond the surface, the sun’s corona heats up dramatically through interactions between plasma and strong magnetic fields. The exact mechanisms of this interaction have been mostly theoretical thus far, but a recent laboratory experiment has validated a part of that theory.

    One explanation for coronal heating posits that the strong magnetic fields can accelerate magnetohydrodynamic waves called Alfvén waves to speeds faster than sound, and that at this crossover point, changes occur in the waves’ behavior. Using liquid rubidium, researchers were able to observe this crossover under laboratory conditions, confirming that the Alfvén waves change at the speed of sound in exactly the manner predicted by theory. (Image credit: NASA SDO; research credit: F. Stefani et al.; via Physics World)

  • Electronic Friction

    Electronic Friction

    Years ago, physicists discovered that water flows with surprisingly little friction through narrow carbon nanotubes. At our scale, flow behavior is typically the opposite: there’s greater friction (and, thus, slower flow) in a narrower pipe. To unravel the mystery, researchers had to delve into quantum mechanics and model the interactions between the atoms of a water molecule and the electrons of the carbon atom. Essentially, this meant building a quantum picture of the liquid-solid interface inside the nanotube.

    The team found that the electrons of the nanotube exert a drag-like force on the water molecules, creating friction that slows the flow. Since narrow nanotubes have fewer electrons than larger tubes, there is less friction on the flow and the water flows faster! (Image credit: cintersimone; research credit: N. Kavokine et al.; via SciAm; submitted by Kam-Yung Soh)

  • Watery Salt Flats

    Watery Salt Flats

    Unusually high rainfall in Bolivia’s Salar de Uyuni turned the world’s largest salt flat into a shallow salt lake. These natural-color satellite images show the area in late January 2022. If you zoom in on the full resolution image, there are incredible detailed swirls in the water. It’s like peering at an abstract or Impressionist painting. The many colors are attributable to several sources, including volcanic sediments, runoff, and a variety of microbes and algae thriving in the mineral-filled waters. (Image credit: L. Dauphin; via NASA Earth Observatory)

  • Spinning Tops

    Spinning Tops

    What does the flow look like around a spinning top? Here, researchers used dye to visualize what happens in a Newtonian fluid (like air or water) as well as a viscoelastic fluid. The Newtonian fluid (upper images) divides into two circulating zones, one below the top and one above. They both take the shape of a toroidal, or donut-shaped, vortex, visible here in cross-section.

    The long molecules of the viscoelastic fluid lend it elasticity to resist stretching. The result is a very different flow field. Beneath the top, there’s still a toroidal vortex, though it appears tighter. But around the upper part of the top, there’s a butterfly-like region of recirculation! (Image credit: B. Keshavarz and M. Geri)

  • Superhydrophobic Drag

    Superhydrophobic Drag

    Using air or bubbles to reduce drag on boats is a popular idea, whether using supercavitation, the Leidenfrost effect, or superhydrophobic coatings. But most of the experiments done thus far use spheres rather than realisitic boat shapes. In this study, the researchers used two model boats — one with a hydrofoil and the other in a conventional motorboat shape — and applied superhydrophobic coatings to different parts of the model to see how superhydrophobicity affected the overall drag.

    Perhaps surprisingly, they found that superhydrophobic coatings can actually increase the drag! The effect was particularly stark for the hydrofoil boat (Image 2), where the surface jets (lower half) caused by the superhydrophobic coating slowed the boat by 30% compared to its unmodified speed (upper half).

    For the speedboat, a superhydrophobic hull made no overall difference in its drag, though it changed how water splashed in its wake. And coating the boat’s propeller was particularly detrimental, resulting in a speed up to three times slower. Overall, the study suggests that superhydrophobic coatings may be useful in some circumstances, but they have to be applied carefully, as they can have negative impacts, too. (Image credits: top – S. Anghan, others and research credit: I. Vakarelski et al.)

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    Eruption in a Box

    In layers of viscous fluids, lighter and less viscous fluids can displace heavier, more viscous liquids. Here, researchers demonstrate this using four fluids sandwiched between layers of glass and mounted in a rotating frame. (Think of those liquid-air-sand art frames found in museums but bigger!)

    In their first example, each layer of fluid is denser than the one beneath it, so buoyancy forces the lowest layer — air — to rise. The air pushes its way through the more viscous layer of olive oil, then slowly makes its way through the even more viscous glycerin before bursting through the last layer in an eruption. As the team varies the viscosity and miscibility of the layers, the movement of the buoyant fluids through the viscous layers changes dramatically. (Image and video credit: A. Albrahim et. al.)

  • Bendable Ice

    Bendable Ice

    Ice — as we typically encounter it — is extremely brittle and easily broken. That’s due to defects in the ice, places where atoms have settled into a spot that does not match the perfect crystalline alignment. Because tiny defect-free threads of ice made by researchers turn out to be wildly flexible!

    To make these perfect ice strands, each of which is a tiny fraction of the thickness of a human hair, researchers applied an electric voltage to a needle in a water-vapor-filled chamber. The technique condensed ice microfibers with perfect crystal structures in a matter of seconds. When bent, the microfibers actually shift from one crystalline arrangement to another in order to carry stress, and once the force is removed, the thread reverts back to its initial straight form. (Image and research credit: P. Xu et al.; via Science News; submitted by Kam-Yung Soh)

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    Columbia Glacier’s Retreat

    In southeastern Alaska, the Columbia Glacier once stretched as far as Heather Island in Prince William Sound. After a long period of stability, the glacier began retreating in 1980 and currently sits more than 15 miles from its previous extent. This video explores the glacier’s evolution through false-color satellite imagery, which allows researchers to distinguish the glacier from sea ice, open water, exposed rocks, and nearby vegetation. Though rapid overall, the glacier’s retreat takes place in fits and starts, due to a combination of influences including climate change, sea and ice interactions, and the effects of local topography. (Video and image credit: NASA Earth Observatory)

    False-color animation showing the retreat of Alaska's Columbia Glacier since 1980.
    False-color animation showing the retreat of Alaska’s Columbia Glacier since 1980.

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