Dancing Droplets: Researchers Solve the Strange Puzzle of Attraction Found in Drops of Food Coloring
A trio of researchers at Stanford recently published an article in Nature that explains the curious attraction found in droplets of everyday food coloring. The paper is the culmination of hundreds of experiments that began in 2009 when Nate Circa was working on an unrelated experiment as an undergraduate at the University of Wisconsin. Circa noticed that when drops of food coloring were placed on a slide they exhibited bizarre behaviors: identical colors would find matches while different colors would seemingly hunt each other.
Circa soon teamed up with Manu Prakash and Adrien Benusiglio who began working on a series of increasingly refined studies to understand why these single droplets appeared to mimic biological processes, resulting in behaviors that looked like chasing, dancing, or avoidance. One of the keys was the interaction of two different compounds found in food coloring: water and propylene glycol. Tom Abate writing for Stanford explains:
The critical fact was that food coloring is a two-component fluid. In such fluids, two different chemical compounds coexist while retaining separate molecular identities. The droplets in this experiment consisted of two molecular compounds found naturally in food coloring: water and propylene glycol. The researchers discovered how the dynamic interactions of these two molecular components enabled inanimate droplets to mimic some of the behaviors of living cells.
This complex behavior is something called artificial chemotaxis which Manu Prakash explains in layman’s terms in the video above:
The physical properties of these fluids give rise to this immense complexity of behavior. For example, chasing and sensing each other, and very much what we call artificial chemotaxis. Chemotaxis is the idea in biology that one single cell can sense where its enemy is, and it brings up all its machinery, and it chases that enemy to try to eat it.
If you really want to get into the nitty gritty of fluid dynamics and molecular physics you can read the full paper in Nature and a bit of a summary on Stanford News. (via, appropriately, F*ck Yeah Fluid Dynamics)
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Researchers at the University of Rochester’s Institute of Optics led by professor Chunlei Guo have developed a new type of hydrophobic surface that is so highly water repellent, it causes water droplets to bounce off like magic. Unlike earlier hydrophobic surfaces that rely on temporary (and slowly degrading) chemical coatings such as teflon, this new super-hydrophobic surface is created by etching microscopic structures into metal with the help of lasers. Potential applications include airplane wings that resist icing, a whole new type of rust proofing, or even a toilet that wouldn’t require water. Watch the video above to see the surface in action, and you can read Guo’s research paper here. (via Sploid)
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If you’ve ever been to a science museum or taken a physics class, you’ve probably encountered an example of a pendulum wave. This video shows a large-scale pendulum wave contraption built on private property in the mountains of North Carolina, near Burnsville. The mechanism relies on 16 precisely hung bowling balls on a wooden frame that swing in hypnotic patterns for a cycle of about 2 minute and 40 seconds. Via Maria Ikenberry who filmed the clip:
The length of time it takes a ball to swing back and forth one time to return to its starting position is dependent on the length of the pendulum, not the mass of the ball. A longer pendulum will take longer to complete one cycle than a shorter pendulum. The lengths of the pendula in this demonstration are all different and were calculated so that in about 2:40, the balls all return to the same position at the same time – in that 2:40, the longest pendulum (in front) will oscillate (or go back and forth) 50 times, the next will oscillate 51 times, and on to the last of the 16 pendula which will oscillate 65 times.
Because the piece is outdoors, a number of factors prevent the balls from precisely lining up at the end, but it’s still easy to get the idea. In a perfectly controlled environment you get something like this.
Update: The pendulum was built by Appalachian State University teacher and artist Jeff Goodman.
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