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Within a Drop
In this macro video, various chemical reactions swirl inside a single dangling droplet. Despite its tiny size, quite a lot can go on in a drop like this. (Video and image credit: B. Pleyer; via Nikon Small World in Motion) Read the full article
Bact Channels
Bacteria grow in sprawling communities – as individual cells divide, so the overall colony grows. The plucky prokaryotes share chemicals with their neighbours, often feeding growth into stubborn biofilms that are difficult to disrupt. Here researchers find another clue to survival in the colony – canals. Pictured under a microscope, this colony of Pseudomonas aeruginosa develops channels (blue) sloshing fluids along each exploratory arm of the colony as it sprawls out. Researchers find that biosurfactant chemicals made by the bacteria help to lower surface tension in the channels, allowing them to send chemical packages called vesicles, or even to travel themselves, like barges on a canal (but 100 million times smaller). The team saw this long-range transport – a form of the Marangoni effect – even in bacteria without hair-like flagella often used to waft chemicals around. Further studies may allow researchers to develop new compounds to break disease-causing colonies apart.
Written by John Ankers
Video by Ye Li and colleagues
Department of Physics, Chinese University of Hong Kong, Hong Kong, China
Video originally published with a Creative Commons Attribution 4.0 International (CC BY 4.0)
Published in eLife, September 2022
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Around 35% of the world’s population (2 billion people) may not have sufficient drinking water to satisfy their daily needs by 2025. That seems crazy when water covers over 70% of the surface of our planet. About 97% of all the water on Earth is in oceans, which is unfortunately...
Solutal Marangoni flows of miscible liquid drive transport without surface contamination
A research team led by Hyoungsoo Kim, a professor of Mechanical Engineering at KAIST, succeeded in quantifying the phenomenon called, the Marangoni effect, which occurs at the interface between alcohol and water. It is expected that this finding will be a valuable resource used for effectively removing impurities from a surface fluid without any contamination, and developing materials that can replace surfactants.
This research, co-conducted with a research team led by Professor Howard A. Stone at Princeton University, was published online in Nature Physics on July 31.
The Marangoni effect, also known as tears of wine, is generated when two fluids having a different surface tension meet, causing finite mixing, spreading time and length scale. Typically, people believe that infinitely miscible liquids immediately mix together; however, it is not always true according to this paper.
The typical surface tension of alcohol is three times lower than that of water, and this different surface tension generates the Marangoni-driven convection flow at the interface of the two liquids. In addition, there is a certain amount of time required for them to mix.
Read more.
Hot Droplets Bounce
In the Leidenfrost effect, room-temperature droplets bounce and skitter off a surface much hotter than the drop's boiling point. With those droplets, a layer of vapor cushions them and insulates them from the hot surface. In today's study, researchers instead used hot or burning drops (above) and observed how they impact a room-temperature surface. (Image and research credit: Y. Liu et al.; via Ars Technica) Read the full article
Dancing Metal Droplets
Droplets of a gallium alloy are liquid at room temperature. When spiked with aluminum grains and immersed in a solution of NaOH, the droplets change shape and move in a random fashion. (Video and image credit: N. Kim) Read the full article
"Trinity"
Inspired by the film Oppenheimer, artist Thomas Blanchard created "Trinity," a short film imagining a nuclear explosion with macro-scale fluid motion. There's clever video editing and compositing in this video, but no CGI. (Video and image credit: T. Blanchard) Read the full article
"Alive Painting"
Artist Akiko Nakayama's intuitive grasp of fluid dynamics is so good that she manipulates liquids live to musical accompaniment. (Image credits: H. Akagi and A. Nakayama; video credit: Eternal Art Space; via Physics World) Read the full article
