This beautifully-made video about a beautifully-colored series of experiments from a Stanford research team showcases how a observing a few droplets of food coloring — made of water and propylene glycol — have led to a deeper study about how two-component fluids behave: chasing, avoiding, attracting… dancing in a “molecular minuet” and more.

Why do the fluids behave this way? Surface tension and evaporation. The two different chemical compounds within the fluids, co-mingling in different proportions, behave differently based on how surface tension and evaporation are affecting each of the compounds within the drops. From Stanford.edu:

Adding colors to the mixtures made it easier to tell how the droplets of different concentrations behaved and created some visually striking results.

In one experiment, a droplet with more propylene glycol seems to chase a droplet with more water. In actuality, the droplet with more water exerts a higher surface tension tug, pulling the propylene droplet along.

In another experiment, researchers showed how physically separated droplets could align themselves using ever-so-slight signals of evaporation.

In a third experiment they used Sharpie pens to draw black lines on glass slides. The lines changed the surface of the slide and created a series of catch basins. The researchers filled each basin with fluids of different concentrations to create a self-sorting mechanism. Droplets bounced from reservoir to reservoir until they sensed the fluid that matched their concentration and merged with that pool.

Learn more about the project at Stanford.edu. Then watch (and do) this next: The Soap Boat Water Experiment.

via Colossal.

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