Image by R. R. La Foy, J. Belden, A. M. Shih, T. T. Truscott, & A. H. Techet
This photo displays a 3 mm wide oil droplet that has hit a pool of rubbing alcohol, as taken by a team from MIT. The drop of oil had light projected on it from both sides, and the difference in refractory index between the two fluids gave the edges of the droplet of oil its bright edges, allowing the artists to take the photo.
It is pretty incredible that through the application of flow visualization techniques, this still of dynamic fluid interaction can even be recorded. Part of what I find fascinating about this picture is the fact that oil is soluble in alcohol, so not only do we see how the combination of fluid densities interact with each other upon impact, but we also have the potential to see the dissolution of the oil as it is introduced to the rubbing alcohol. This photo is only the first in a series of several photos that show the droplet of oil as it continues to fall through the alcohol and dissolve.
Link to full article (download the PDF): http://dspace.mit.edu/handle/1721.1/79362