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.
The beauty of science is everywhere around us. One of the things that really grabbed our attention in this work was the organic notion of what was happening. It’s literally as if these droplets are dancing.
I studied something entirely different back when I was several undergraduate years ago and stumbled on this phenomenon quite by accident. Even to my naked eye, the droplets were moving around on the glass slide. I was really surprised. I’d never seen that, and that seemed really, really strange and really new, and also very beautiful.
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.
In food coloring, there’s a small molecule called propylene glycol. The droplets consist of this molecule mixed with water. It turns out that the system’s binary nature, the fact that there are two fluids, and the fact that they evaporate at different rates and have different surface tensions are critical for observing this phenomenon.
Many classes of two liquids mixed will exhibit these phenomena. There is this juxtaposition of what is simple and what is complex. Everyday phenomena are very, very simple when you look and observe them, but it ends up many layers of complexity if you understand them. And that is why, to me, it is personally very exciting.