Search results for: “surface tension”

“Chemical Poetry”
In “Chemical Poetry” artists Roman Hill and Paul Mignot use fluid dynamics to create incredible and engaging visuals. With a stunningly close eye to fluids mixing and chemicals reacting, their imagery feels like gazing on primordial acts of creation or destruction. There’s even a sequence that feels like you’re watching an explosion in slow-motion, but there’s no CGI in any of it. This is just the beauty of physics laid bare, revealing the dances driven by surface tension, the undulations of a fluid’s surface, and the dendritic spread of one fluid into another – all cleverly lit and filmed for maximum effect. It is well worth taking the time to watch the whole video and check out more of their work. (Image/video credit and submission: NANO; GIFs via freshphotons)
November 30, 2016
Coarsening in a Soap Film
Flow in a soap film is driven by gravity’s efforts to thin the film and surface tension’s attempts to stabilize variations in thickness. Because evaporation guarantees that the soap film will eventually dry out, gravity typically wins the battle and causes a soap film to rupture. This video takes a close look at what happens in the film just before it ruptures. Black dots form in the thinnest region of the flow. These areas are not holes, but they appear black because they are thinner than any wavelength of visible light. Before rupture, the black dots begin coalescing with one another, first due to diffusion and later more rapidly due to convection in the soap film. Ultimately, the black dots are the harbingers of doom for the fragile bubble. (Video credit: L. Shen et al.)
November 22, 2016
A Particle-Filled Splash
A drop of water that impacts a flat post will form a liquid sheet that eventually breaks apart into droplets when surface tension can no longer hold the water together against the power of momentum flinging the water outward. But what happens if that initial drop of water is filled with particles? Initially, the particle-laden drop’s impact is similar to the water’s – it strikes the post and expands radially in a sheet that is uniformly filled with particles. But then the particles begin to cluster due to capillary attraction, which causes particles at a fluid interface to clump up. You’ve seen the same effect in a bowl of Cheerios, when the floating O’s start to group up in little rafts. The clumping creates holes in the sheet which rapidly expand until the liquid breaks apart into many particle-filled droplets. To see more great high-speed footage and comparisons, check out the full video. (Image credit and submission: A. Sauret et al., source)
November 16, 2016
Colors in Macro
Milk, acrylic paints, soap, and oil – all relatively common fluids, but together they form beautiful mixtures worth leaning in to enjoy. Variations in surface tension between the liquids cause much of the motion we see. Soap, in particular, has a low surface tension, which causes nearby colors to get pulled away by areas with higher surface tension, behavior also known as the Marangoni effect. Adding oil creates some immiscibility and lets you appreciate both the coalescence and fragmentation of the fluids. And finally, there’s one of my favorite sequences, where bubbles start popping in slow motion. As the bubble film ruptures, fluid pulls away, breaking into ligaments and then a spray of droplets as the bubble disintegrates. (Video credit: Macro Room; via Gizmodo)
November 11, 2016
Supercritical
Supercritical fluids are neither a gas nor a liquid. The video above shows a tube of pressurized xenon, initially below its boiling point of approximately ~16 deg C. As the temperature is raised, you see the meniscus that marks the liquid xenon disappear. At this point, the xenon has transitioned into the supercritical state. It takes up the entire tube – like a gas – but it is still capable of dissolving materials – like a liquid. At the same time, though, the xenon has no surface tension because there’s no liquid/vapor interface. Toward the end of the video, the temperature gets reduced and the xenon condenses back into a liquid state. Supercritical fluids can be used in a wide variety of industrial applications, including in decaffeination, dry cleaning, and refrigeration. (Video credit: wwwperiodictableru)
November 3, 2016
Dripping, Frozen
The simple drip of a faucet is more complicated when frozen in time. Any elongated strand of water tends to break up into droplets due to surface tension and the Plateau-Rayleigh instability. Whenever the radius of the water column shrinks, surface tension tends to drive water away from the narrow region and toward a wider point. This exaggerates the profile, making narrow regions skinnier and wider regions fatter. Eventually, the neck connecting the droplets becomes so thin that it pinches off completely, leaving a string of falling droplets. (Image credit: N. Sharp)
October 20, 2016
Hummingbird Drinking
Hummingbirds are master acrobats, able to hover and drink simultaneously before flitting off to the next flower. At first glance, you might expect that their tongues are simply tiny straws that use surface tension and capillary action to draw up nectar. But it turns out that process is just too slow for the fast-paced birds.
Instead, hummingbirds use a forked tongue with a long groove on either half. When the hummingbird extends its tongue, its beak compresses the grooves and squeezes them together. Once the tongue reaches nectar, the grooves expand, which draws nectar up along the full length of the tongue grooves. This allows the bird to fill its tongue much faster than it could otherwise, enabling the hummingbird to lick up nectar more than 10 times a second.
There’s a neat excerpt from a documentary including this research over here (Tumblr won’t allow the embedded version); the full documentary premieres today on PBS. (Image credits: A. Rico-Guevara et al., sources 1,2; submitted by mypronounsareherrchancellor)
October 12, 2016
A Molecular View of Boiling
All matter is made up of molecules. But most of the time we treat fluids as materials with given properties – like density, viscosity, and surface tension – without worrying about the individual molecules responsible for those material characteristics. Now that we have much more powerful computers, though, we can begin to simulate fluid behavior in terms of molecules.
The animations above show some examples of this. In the top animation, we see a gas condensing into a liquid. As the temperature decreases, molecules start clumping together, and eventually settle into a droplet on the solid surface. The lower animation shows the opposite situation – boiling – in which bubbles of vapor nucleate next to the solid surface and grow as more liquid changes phase. To see more examples, including droplets pinching off, check out the full video. (Image credit: E. Smith et al., source; submitted by O. Matar)
October 7, 2016
Soap Film Turbulence
The brilliant colors of a soap film reveal the fluid’s thickness, thanks to a process known as thin film interference. The twisting flow of the film depends on many influences: gravity pulls down on the liquid and tends to make it drain away; evaporation steals fluid from the film; local air currents can push or pull the film; and the variation in the concentration of molecules – specifically the surfactants that stabilize the film – will change the local surface tension, causing flow via the Marangoni effect. Together these and other effects create the dancing turbulence captured above. (Video credit: A. Filipowicz)
September 20, 2016
Droplet Bounce
Water droplets don’t always immediately disappear into a pool they’re dropped onto. If the droplet is small and doesn’t have much momentum, it will join the pool gradually through a process known as the coalescence cascade, seen here in high speed video. The droplet bounces off the surface, then settles. A thin layer of air is caught between it and the pool. Slowly the weight of the drop pushes that air out until there is contact between the drop and pool. Before the drop can merge completely, though, surface tension pinches it off, creating a smaller daughter droplet. Ripples caused by the merger help bounce the little droplet, which repeats the same process until the tiniest droplet merges completely. (Video credit: B. ter Huume)
September 13, 2016

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