Looks a bit like the Dance of the
Sugar Plum Fairies,
if they were made of water
and propylene glycol.
That's the key.
Each droplet is composed of two fluids.
The coloring is just to help you
see what's going on.
The different fluids evaporate
at different rates, and they
have different surface tension.
And the result, in each droplet,
is kind of a constant internal tornado.
Scientists at Stanford found that if
that internal tornado is disrupted,
then the droplets chase each other around,
or form a line,
or even climb vertically.
And the reason is that just a hint of
evaporation from one drop
changes the relative humidity
near the surface of the other drop.
The change in humidity affects how the
water evaporates from the other drop.
That changes its internal tornado,
and the drop starts to move.
The result is totally fun to look at,
and it could be a brilliant teaching tool.
Simple materials,
complicated physics.