A time lapse image of a dyed water droplet falling into a mixture of oil and water. The droplet's coalescence can be manipulated with an electric field.
Image Credit: American Physical Society/B.S. Hamlin et al.
For this image, researchers dropped a dyed water droplet into a larger bath of oil and water. The oil and water bath also had two electrodes in it that generated an electric field. If this external field is strong enough, the water droplet will simply bounce off of the oil/water mixture upon contact. At low intensity fields, however, the water droplet will completely combine -- or coalesce -- with the mixture. Fields in the intermediate range can produce striking images of partial coalescence, as seen above.
Physics research behind this image
APS Division of Fluid Dynamics