Bird’s nest fungi are tiny — only about a centimeter wide. When mature, they form a curved splash cap containing spore sacs known as peridioles. Then they await rain. When a lucky drop hits the mushroom, it flings the peridioles out of their nest. Some will use sticky cords to cling to nearby blades of grass, setting them up to eventually hitch a ride to elsewhere with a grazing herbivore. It’s an impressive journey for a teeny spore sac, and it all starts with a single drop of rain. (Image and video credit: Deep Look)
Without surfactants to stabilize them, bubbles don’t last long at room temperature. But adding a little heat changes the picture. When heated, the bubbles get stabilized by a thermal gradient that lifts fluid toward the bubble’s peak, where it cools and gathers. Eventually, the cold fluid grows heavy enough to sink down the side of the bubble (in either a constant stream or occasional drips); with warm fluid getting pulled up to replace it (via the Marangoni effect), the process repeats and the bubble lives on. (Video credit: S. Nath et al.; see also)
When bubbles burst, they release smaller droplets from the jet that rebounds upward. Depending on their size, these droplets can fall back down or get lofted upward on air currents that spread them far and wide. Thus, knowing what kind of bubbles produce small, fast droplets is important for understanding air pollution, climate, and even disease transmission.
The jet from a bubble of clean water is broad and slow, releasing fewer and larger drops.
In a recent study, researchers compared droplets made by clean, water-only bubbles, and the ones generated from water bubbles with a thin layer of oil coating them. The clean bubbles created jets that were broad and relatively slow moving; this motion produced a few large drops that quickly fell back down.
The jet from an oil-covered bubble is skinny and fast-moving. It produces many small droplets.
In contrast, the oil-slicked bubbles made a narrow, fast-moving jet that broke into many small droplets. These droplets could stay aloft for longer periods, indicating that contaminated water can produce more aerosols than clean. (Image credit: top – J. Graj, bursting – Z. Yang et al.; research credit: Z. Yang et al.; submitted by Jie F.)
Droplets with particles in them can leave complex stains when they dry — just look at coffee rings and whiskey marks! Here, researchers look at the patterns left on glass by small droplets that evaporated and left behind their nanoparticles. As evaporation takes place, the droplet’s shape changes, adding stress to the growing layer of nanoparticle residue. Cracking is one way to relieve that stress. Another method is delamination — peeling up from the surface. On the leftmost drop, the outer rim of nanoparticles delaminated — as seen from the circular fringes — which released stress without cracking. The rightmost drop, which had a smaller contact angle with the surface, couldn’t delaminate and instead cracked throughout. (Image credit: M. Ibrahim et al.)
Mammatus clouds are fairly unusual and often look quite dramatic. Most clouds have flat bottoms, caused by the specific height and temperature at which their droplets condense. But mammatus clouds have bubble-like bottoms that are thought to form when large droplets of water or ice sink as they evaporate. Although they can occur in the turbulence caused by a thunderstorm, mammatus clouds themselves are not a storm cloud. They appear in non-stormy skies, too. The clouds are particularly striking when they’re lit from the side, as in the image above. (Image credit: J. Olson; via APOD)
Springtails are small, jumping insects. Semiaquatic varieties use their tails to jump off water in order to move around and escape predation. Among these water jumpers, results vary; some, like in the third image, have little to no control over their landings and will frequently faceplant or land on their backs. But some species in the family have a better technique.
These springtails grab a water droplet with their hydrophilic ventral tube (seen in the second image with a red identifying arrow) during take-off. This tiny water droplet serves several purposes. First, it adds extra weight to the insect, allowing it to better orient its body to land belly-down. Second, the drop gives the insect a way to adhere to the water during landing, preventing it from bouncing. Check out the video to see lots of high-speed video of these tiny acrobats! (Video and image credit: A. Smith/Ant Lab; research credit: V. Ortega-Jimenez et al.)
The tiny glassy-winged sharpshooter feeds exclusively on nutrient-poor sap from plant xylem. Since the sap is 95% water, the insects have to consume massive amounts, necessitating lots of urination — up to 300 times their body weight each day! With so much urine to get rid of and so little energy to spare, the sharpshooter has developed an ingenious, low-energy method to expel its waste. The insect forms a droplet on its anal stylus and flings it. A recent study reveals just how clever the insect’s method is.
Researchers found that sharpshooters fling their droplets 40% faster than their stylus moves. This superpropulsion is only possible because the stylus’s motion is finely tuned to the droplet’s elasticity. Essentially, the insects achieve single-shot resonance with every throw. The energy-savings for the insects is substantial; researchers estimate that making a jet of urine instead would cost four to eight more times energy. (Video credit: Georgia Tech; image and research credit: E. Challita et al.; via Ars Technica; submitted by Kam-Yung Soh)
Giant iridescent inflatables dot public spaces in the “Evanescent” exhibit. The “bubble-tecture” is the work of Sydney-based artistic collaboration Atelier Sisu. Conceived during the pandemic, the duo “endeavoured to communicate this feeling of transient beauty and the need to live in the moment through the idea of the bubble.” The exhibit has appeared in more than 22 cities in 12 different countries. (Image credit: Atelier Sisu; via Colossal)
We see plenty of droplets splash when they fall into a pool, but what happens when the drop and pool are two-dimensional? Here researchers captured the familiar process of a splash in an unfamiliar way by looking at a falling drop contained within a soap film. As the drop reached the thicker lower boundary of the soap film (which acts like a pool), its impact sent up ejecta that stretch and curl, much like the three-dimensional splashes we’re accustomed to. (Image credit: A. Alhareth et al.)
A group of excited atoms can collectively emit more photons than they could individually in a phenomenon known as superradiance. Now researchers have shown that vibrating fluids can produce superradiance as well.
Two different wave fields used in the experiment, each with a different distance between the circular cavities.
Similar to other hydrodynamic quantum analogs, the researchers vertically vibrated a pool of liquid at a frequency that produced Faraday waves. Beneath the pool, they placed two circular wells, varying the distance between them to observe how their wave fields interacted. With a large enough vibration, the two circular wells emitted droplets (top image), and the number of droplets they produced was higher than expected for two independent wells, indicating superradiance. The results suggest that it may be possible to build even more hydrodynamic analogs of quantum systems than previously thought! (Image and research credit: V. Frumkin et al.; via APS Physics)
