Visualizing Air Around a Splashing Drop

It is well known that when a drop impacts a surface at a large enough velocity it will splash. ~However, it was recently discovered that removing the surrounding air from a drop can suppress splashing completely. ~This discovery still remains unexplained. ~Not only is it not understood why the air matters but it is also not even known where the liquid-air interaction is important: ~Is it beneath the drop, is it at the drop's edge or is it at the drops upper surface? ~~Using modified schlieren optics combined with high-speed video imaging, we were able to visualize vortices in the air~that were created when the drop~spread out rapidly after~hitting the substrate. ~~These vortices~varied with impact velocity and splash type. ~We are currently measuring the strength of forces created by the air on the upper surface of the drop in order to confirm our tentative conclusion that~it is the air above the spreading drop that plays the dominant role in creating a splash.