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.