Breaking a jet of liquid into droplets lies at the heart of many industrial processes: spray painting, fuel injection, and asthma inhalers, to name a few. Here, researchers are looking at a different method of breaking up a liquid jet: shooting a shock wave along its length. The poster shows five different snapshots of the jet’s response. There are, variously, mists of fine droplets, wavy distortions of the jet, sheets, ligaments, and droplets of many sizes. (Image credit: S. Rao et al.)
On a vibrating fluid, droplets can bounce and interact in complex ways. Here, researchers demonstrate some of the peculiar dynamics of these wave-guided droplets, showing how they can do things like pair up in waltzes. To keep the droplets from coalescing with one another, they perform their experiments in a pressurized chamber; the higher air pressure makes it harder for the air film between droplets to drain during a collision, making the droplets unable to coalesce. Under these conditions, the authors show that the droplet-wave system has quantum-like statistics. (Video and image credit: J. Clampett et al.)
Although water can freeze below 0 degrees Celsius, it requires a little help–in the form of a nucleation site–to do so. Often temperatures must dip well below 0 degrees Celsius for droplets to become ice. But a new study shows that at least one fungus forms proteins that help the process along.
The proteins come from the Mortierellaceae fungal family, by way of a bacterial species some hundreds of thousands of years ago or more. In experiments, adding the fungal protein helped water freeze 10 or more degrees Celsius sooner than it otherwise would.
The authors note that there are many possible applications for this freezing additive; it could help preserve food or cells without requiring lower freezing temperatures that could damage delicate tissues. It could also serve as a cloud seeding chemical in place of toxic silver iodide particles. (Image and research credit: R. Eufemio et al.; via Gizmodo; see also V. Tech)
Many industrial processes break a fluid jet into droplets, like spray painting and ink-jet printing. Here, researchers examine an effervescent fluid jet made up of both liquid and gas. Like a fluid-only jet, this fizzy jet forms sheets, bags, ligaments, and droplets. As it breaks down, it creates a range of droplet sizes–both large and small. But when a shock wave passes, the jet and its droplets get atomized into even tinier droplets. (Video and image credit: S. Rao et al.)
When air bubbles rise through a liquid, they scavenge dust, viruses, microplastics, and other impurities as they go. Once at the surface, these contaminant-covered bubbles thin and burst, generating many tiny droplets that arc through the air above. You’re likely familiar with the sight and sensation from a glass of champagne or soda.
Here, researchers have stacked two sets of sequential images to illustrate this complicated flowscape. Under the surface, a trio of photos are stacked to show bubbles rising and gathering at the surface. In the air, the researchers have stacked thirty sequential images, which together trace out the parabolic arcs of droplets sprayed by the bursting bubbles. (Image credit: J. Do and B. Wang)
Over the last 15 years or so, researchers have been exploring pilot-wave theory–originally proposed by De Broglie in the 1920s as a way to understand quantum mechanics–using hydrodynamic quantum analogs. In these experiments, researchers vibrate pools of silicone oil, which allows oil drops to bounce–and in some conditions, walk–indefinitely on the pool. By mixing in obstacles that mimic classic quantum mechanical experiments, they reproduce effects like the double-slit experiment in a macroscopic system.
In this video and the accompanying papers, a team recreates the Kapitsa-Dirac effect where a standing electromagnetic wave diffracts electrons. Here, the standing wave is instead a Faraday wave in the surface of the pool. Yet the droplets, too, diffract in a manner resembling the quantum version. (Video credit: B. Primkulov et al.; research credit: B. Primkulov et al. 1, 2)
For tiny invertebrates like this one, water is a very different substance than we’re used to. At this scale, surface tension is a force as powerful–or more so–than gravity. Droplets remain spherical, caught on long, spike-like hairs. Even the surface of a pond is different, forming a trampoline creatures can skim but that requires special techniques to escape. (Image credit: N. Baumgartner/CUPOTY; via Colossal)
Light shining through misty spray creates a liquid rainbow in this photo by Ronja Linssen. Although mists and sprays–from waterfalls, waves, and more–seem insubstantial, they can be a major source of material transfer between the water and atmosphere. Teratons of salt, biomass, and even microplastics make their way yearly from the ocean into the sky through droplets launched from popping bubbles. (Image credit: R. Linssen/CUPOTY; via Colossal)
Grains of pollen are caught amid droplets on a spider’s web in this award-winning image by John-Oliver Dum. How droplets behave on fibers has been a popular topic in recent years with research on how droplets nestle into corners, how they slide on straight or twisted wires, the patterns formed by streams of falling drops, and what happens to a droplet on a plucked string. (Image credit: J. Dum; via Ars Technica)
On the surface of a gently vibrating liquid, a droplet can bounce indefinitely without coalescing, kept aloft by an air film too small to see. As long as the droplet lifts off before the air layer drains out from under it, the droplet won’t contact the water below. Now scientists have shown that this is possible with a solid surface, too.
Using an atomically smooth mica plate, researchers were able to bounce a droplet indefinitely without wetting the surface. At higher vibration rates (below), the droplet essentially hovers in place, bouncing so quickly that we simply see its shape vibrating in response to the surface. (Image and research credit: L. Molefe et al.; via APS)
