Al Seckel, a cognitive neuroscientist and expert on illusions, created this “Levitating Water” installation, in which multiple streams of water appear as a series of levitating droplets thanks to a strobing light. The well-timed strobe lighting tricks the brain into seeing many different falling droplets as the same, nearly stationary droplet. The effect is similar to the one created by vibrating a stream of falling water. (Video credit: wunhanglo)
Search results for: “water droplet”
Droplet Bounce
This high-speed video shows the remarkable resilience of a water droplet upon impact against as a solid surface. The droplet deforms into a pancake-shape, with its center depressing almost flat before rebounding upward. The rest of the drop follows, splitting into several droplets as capillary waves dance across its surface. When one satellite drop almost escapes, the main droplet just barely comes in contact with it, the coalescence enough to tip surface tension into pulling them together instead of breaking them apart. (Video credit: K. Suh/ChemistryWorldUK)
Breaking into Droplets
A falling column of liquid, like the water from your faucet, will tend to break up into a series of droplets due to the Plateau-Rayleigh instability. This instability is driven by surface tension. Small variations in the radius of the column occur naturally. Where the radius shrinks, the pressure due to surface tension increases, causing liquid to flow away, which shrinks the column’s radius even further. Eventually the column pinches off and breaks into droplets. What’s especially neat is that the size of the final droplets can be predicted based on the column’s initial radius and the wavelength of its disturbances. (Video credit: BYU Splash Lab)
Encapsulating Droplets
In applications like drug delivery, it’s often desirable to encapsulate one or more liquid droplets in an additional immiscible fluid. These drops-within-drops, called double emulsions, are typically a multi-step process, created from the innermost drop outward. In this new microfluidic technique, though, researchers are able to create multi-component emulsions in a single step. A double-bored capillary tube creates the two inner droplets (both water, dyed different colors) while oil flows down the outside of the injection tube to encapsulate the droplets. The multi-component double emulsions then flow as one to the right in the outer carrier fluid. The spacing of the capillary tubes is critical to prevent the inner droplets from coalescing with one another. (Video credit: L. L. A. Adams et al.)
Shocking Droplets
Typical liquid drops will break apart into long, stretched ligaments and a spray of tiny droplets when deformed. But with just a small addition of polymers, these same liquids become viscoelastic and capable of some pretty incredible behaviors. This video shows a viscoelastic drop being struck by a shock wave that passes from right to left. The droplet is smashed and deformed, then stretches into jellyfish-like sheet of liquid. But incredibly, the elastic forces in the droplet are enough to hold it together. Researchers are interested in understanding these behaviors for many applications, including preventing accidental explosions caused by explosive fuels atomizing in air. (Video credit: T. Theofanous et al.)
Bouncing to Mix Oil and Water
Mixing immiscible liquids–like oil and water–is tough. The best one can usually do is create an emulsion, in which droplets of one fluid are suspended in another. The series of images above shows a double emulsion consisting of oil and water that’s been formed by bouncing the compound droplet on a vibrating bath. The vibration of the liquid surface keeps the droplet from coalescing with the bath and the deformation provides mixing. The top row shows the initial impact while the bottom row of images shows the droplet after many bounces. As time goes on, the layer of oil around the compound drop becomes a cluster of tiny droplets contained within the water portion of the drop. (Photo credit: D. Terwagne et al.)
Skittering Droplets
Water splattered onto a a hot skillet will skitter and skip across the surface on a thin layer of vapor due to the Leidenfrost effect. The partial vaporization of the droplet provides a low-friction cushion for the droplet to glide on and acts as an insulating layer that delays the vaporization of the rest of the droplet. Modernist Cuisine shows us how serene this common and sometimes explosive effect looks at 3,000 frames per second. (On the topic of cooking, you can use the Leidenfrost effect to see if your skillet is hot enough when making pancakes. If a few droplets of water skitter across the pan before sizzling away, then your pan is ready for batter!) (Video credit: Modernist Cuisine; submitted by Eban B.)
Making Metal Water-Repellent
Chemical treatments can be used to render metals hydrophobic, causing water to bead on the surface rather than spreading to wet it. Treating the surface by immersing it in boiling water before applying the chemicals creates a nanoscale texture that accentuates the hydrophobicity. Even on a common metal like aluminum, this combination of texturing and chemical treatment leads to superhydrophobic behavior. Here the technique is demonstrated by spraying water droplets on a piece of treated aluminum. (Video credit: B. Rosenberg et al.; submitted by D. Quinn)
Spitting Droplets
Any phenomenon in fluid dynamics typically involves the interaction and competition of many different forces. Sometimes these forces are of very different magnitudes, and it can be difficult to determine their effects. This video focuses on capillary force, which is responsible for a liquid’s ability to climb up the walls of its container, creating a meniscus and allowing plants and trees to passively draw water up from their roots. Being intermolecular in nature, capillary forces can be quite slight in comparison to gravitational forces, and thus it’s beneficial to study them in the absence of gravity.
In the 1950s, drop tower experiments simulating microgravity studied the capillary-driven motion of fluids up a glass tube that was partially submerged in a pool of fluid. Without gravity acting against it, capillary action would draw the fluid up to the top of the glass tube, but no droplets would be ejected. In the current research, a nozzle has been added to the tubes, which accelerates the capillary flow. In this case, both in terrestrial labs and aboard the International Space Station, the momentum of the flow is sufficient to invert the meniscus from concave to convex, allowing a jet of fluid out of the tube. At this point, surface tension instabilities take over, breaking the fluid into droplets. (Video credit: A. Wollman et al.)
The Water Bridge
This short film offers an artistic look at the phenomenon of the water bridge. When subjected to a large voltage difference, such as the 30 kV used in the film, flow can be induced between water in two separated beakers. This creates a water bridge seemingly floating on air. There are two main forces opposing the bridge: gravity, which causes it to sag, and capillary action, which tries to thin the bridge to the point where it will break into droplets. These forces are countered by polarization forces induced at the liquid interface due to the electrical field separating the water’s positive and negative charges. This separation of charges creates normal stresses along the water surface, which counteracts the gravitational and capillary forces on the bridge. The artist has done a beautiful job of capturing the unsteadiness and delicacy of the phenomenon. (Video credit: Lariontsev Nick)