FYFD

Search results for: “droplet”

  • Featured Video Play Icon

    Rattlesnakes Sip Rain From Their Scales

    Getting enough water in arid climates can be tough, but Western diamondback rattlesnakes have a secret weapon: their scales. During rain, sleet, and even snow, these rattlesnakes venture out of their dens to catch precipitation on their flattened backs, which they then sip off their scales.

    Researchers found that impacting water droplets tend to bead up on rattlesnake scales, forming spherical drops that the snake can then drink. Compared to other desert-dwelling snakes, Western diamondbacks have a far more complicated microstructure to their scales, with labyrinthine microchannels that provide a sticky, hydrophobic surface for impacting drops. (Video and image credit: ACS; research credit: A. Phadnis et al.; via The Kid Should See This)

  • Featured Video Play Icon

    Bouncing Off Defects

    The splash of a drop impacting a surface depends on many factors — among them droplet speed and size, air pressure, and surface characteristics. In this award-winning video from the 2019 Gallery of Fluid Motion, we see how the geometry of a superhydrophobic surface can alter a splash.

    When a drop falls on a protruding superhydrophobic surface, like the apex of a cone, it can be pierced from the inside, completely changing how the droplet rebounds and breaks up. The variations the video walks us through are all relatively simple, but resulting splashes may surprise you nevertheless. (Image and video credit: The Lutetium Project)

  • Featured Video Play Icon

    “Viscoelasticity Gives You Wings!”

    What happens when you drop a hydrogel bead on a water droplet? Because of the hydrogel’s viscoelasticity and its hydrophilic nature, the rebounding bead carries the droplet with it. As seen in the video above, when the impact energy is small enough, the droplet forms a reverse crown during lift-off, kind of like giving the hydrogel bead a skirt. The key feature for lift-off is the bead’s deformation on impact. Because the hydrogel widens at its base, it is sometimes able to push the entire droplet off its initial footprint and detach it from the surface. (Image, research, and video credit: R. Rabbi et al.)

  • Featured Video Play Icon

    Blowing Vortex Rings from Bubbles

    When bubbles burst, we often pay attention to the retracting film and forming droplets, but what happens to the air that was inside? By placing a little smoke inside them, we can see. The air inside these bubbles is slightly pressurized compared to the ambient, and as such a bubble ruptures, its air gets pushed out the expanding hole. That momentum makes the air curl as it forces its way into the surrounding air, creating a stack of vortex rings. The researchers observed as many as six stacked vortices from bubbles just under 4 cm in diameter. (Image and research credit: A. Dasouqi and D. Murphy; video credit: Science; see also A. Dasouqi and D. Murphy)

  • Featured Video Play Icon

    Waltzing Defects

    Liquid crystals are a peculiar state of matter with both liquid and crystalline properties. In this video, a microfluidic device breaks water into droplets surrounded by a shell of liquid crystal. Because the molecular structure of the liquid crystals is helical and cannot pack neatly in a spherical shell, there are visible defects in the liquid crystal shells. Given time, those defects can merge as the liquid crystal shell thickens. (Image and video credit: The Lutetium Project)

  • Featured Video Play Icon

    Blooming Deposits

    Evaporate a droplet full of silica nanoparticles, and you’ll get beautiful, flower-like films. As the water evaporates, dry nanoparticles build up in a solid deposit. The evaporation creates a pressure gradient that pulls toward the center of the drop, forcing the deposit to bend. As stress builds in the deposit, cracks form petal-like segments. The number of cracks is indicative of how much of the drop was solid material; the higher the volume fraction of particles is, the fewer cracks form and the less the deposit bends. (Image, video, and research credit: P. Lilin et al.)

  • Falling Drops and Forming Stalagmites

    Falling Drops and Forming Stalagmites

    The vast stalactites and stalagmites found in caves take millennia to form. Mineral-rich water seeps down the icicle-like stalactites and then drips onto stalagmites below, each drop depositing a little more calcite onto the growing rock. By observing this dripping action first-hand, researchers found that most falling drops create a splash that’s much smaller than the width of the stalagmite they fall onto. So how do stalagmites end up so wide?

    It turns out that there’s a large variance in where drops hit the stalagmite. There’s no wind in these caves to push the droplets, so researchers concluded the drop’s trajectory depends on the vortices it sheds as it falls. A drop that falls from a short height will have a vertical trajectory. But once the drop is falling tens of meters, it can end up as many as several centimeters to the side of where it would fall in a vacuum. This scatter-shot variation in drop impacts is what enables stalagmites to grow so wide. (Image and research credit: J. Parmentier et al., source; via NYTimes; submitted by Kam-Yung Soh)

  • CU Flow Vis 2019

    CU Flow Vis 2019

    I love when science and art come together, which is why I’ve long been a fan of the Flow Vis course at CU Boulder. Some of my earliest posts on FYFD date from previous editions of the course. Here are a few of my favorite images from the Fall 2019 class, from the top:

    •  Ferrofluid and India ink merge in this colorful photo. A magnet underneath the mixture on the left side causes the dark spikes of ferrofluid, but without magnetic influence, the ink and ferrofluid form cell-like droplets.
    • Although it looks like a shower head, this is actually fluorescent oobleck dripping through a strainer. A relatively long exposure time means that it’s impossible to tell whether the oobleck is falling in a fluid stream or broken-up chunks.
    • These colorful water droplets are sitting on a hydrophobic surface, hence their extremely rounded edges. I particularly like how this makes each one like a little lens for the light shining through them and into their shadows.
    • A thin layer of ferrofluid reacts to the magnet beneath. Gotta love those little streaks left behind the flow.

    For those in the Front Range area, the Flow Vis class will be showcasing their work on Saturday, December 14th at the Fiske Planetarium. Snacks are at 4:30 pm and the show starts at 5 pm. For those not nearby, you can peruse the art from this semester and previous ones at your leisure online. (Image credits: colorful ferrofluid – R. Drevno; falling oobleck – A. Kumar; droplets – A. Barron; macro ferrofluid – A. Zetley)

  • Making Drops Stick

    Making Drops Stick

    As you may have noticed when washing vegetables, many plants have superhydrophobic leaves. Water just beads up on their surface and slides right off. This is a useful feature for plants that want to direct that water toward their roots, but it’s a frustration in agriculture, where that superhydrophobicity means extra spraying of pesticides in order to get enough to stick to the plant.

    But that may not be the case for much longer. Researchers have found that adding a little polymer to water droplets (right) can suppress their ability to rebound (left) from superhydrophobic surfaces. Above a critical concentration, the high shear rate of the droplet as it tries to detach activates the viscoelastic properties of the polymer. That viscoelasticity suppresses the rebound, keeping the droplet attached. That’s good news for everyone, since it means less spraying is needed to protect crops. (Image and research credit: P. Dhar et al.)

  • Whiskey Stains

    Whiskey Stains

    Complex fluids leave behind fascinating stains after they evaporate. We’ve seen previously how coffee forms rings and whisky forms more complicated stains as surface tension changes during evaporation drive particles throughout the droplet. Now researchers are considering the differences between traditional Scottish whisky, which ages in re-used, uncharred barrels, and American whiskeys like bourbon, which are required to age in new, charred white oak barrels.

    When diluted, the American whiskeys form web-like patterns – seen above – that vary from brand to brand, like a fingerprint. The charring of the barrels allows American whiskeys to pick up more water-insoluble molecules compared to whisky aged in uncharred barrels. Since the webbed patterns form in American whiskey but not Scotch whisky, it’s likely those molecules play an important role in the evaporation dynamics and subsequent staining. (Image credit: S. Williams et al.; research credit: S. Williams et al.; via APS Physics; submitted by Kam-Yung Soh)

More posts