#dancing droplets

[thewightknight]

Under certain circumstances, droplets of fluid will move like performers in a dance choreographed by molecular physics.

(x)

[ravenblackhart]

Nate Cira spent years studying the phenomenon of dancing water droplets that he had chanced across while doing an unrelated experiment, where he had deposited several droplets of food coloring onto a sterilized glass slide. “These droplets sense one another, they move and interact, almost like living cells”, said Manu Prakash, an assistant professor of bioengineering. 

Cira replicated and studied this phenomenon alone for two years until he became a graduate student at Stanford, where he shared this curious observation with Prakash. The professor soon became hooked by the puzzle, and recruited a third member to the team: Adrien Benusiglio, a postdoctoral scholar in the Prakash Lab.

Together they spent three years performing increasingly refined experiments to learn how these tiny droplets of food coloring sense one another and move. In living cells these processes of sensing and motility are known as chemotaxis.

Essentially, the droplets danced because of a delicate balance between surface tension and evaporation. Water evaporates more quickly than propylene glycol - a common ingredient in food colouring. Water also has a higher surface tension.  These differences create a tornado-like flow inside the droplets, which not only allows them to move but also allows a single droplet to sense its neighbors.

Evaporation happens more readily on the thin lower edges of the domed droplet, leaving excess of propylene glycol there. Meanwhile, the peak of the dome has a higher concentration of water.The water at the top exerts its higher surface tension to pull the droplet tight so it doesn't flatten out. This tugging causes a tumbling molecular motion inside the droplet. Thus surface tension gets the droplet ready to roll.

The researchers experimented with varied proportions of water and propylene glycol. Based on these experiments, they describe a "universal rule" to identify any two-component fluids that will demonstrate sensing and motility.

The unexpected findings may prove useful in semiconductor manufacturing and self-cleaning solar panels, as effect is present on a large number of common surfaces and can be replicated with a number of chemical compounds.

(Source: Stanford News )

[mytreetv]

Dancing droplets!

Dancing droplets! @Stanford

A puzzling observation, pursued through hundreds of experiments, has led Stanford researchers to a simple yet profound discovery: Under certain circumstances, droplets of fluid will move like performers in a dance choreographed by molecular physics. Read the story:http://stanford.io/1A9EcAE

Nice Logo by the way:

http://www.stanford…

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[tooblackforbreakfast]

Via This Is Colossal: 

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)