Entrapment of air bubbles under a drop

In collaboration with Professors Etoh and Takehara, I am studying the entrapment of small air bubbles when a drop impacts onto a pool of liquid.  A very thin sheet of air is caught under the center of the drop, as all the air does not have time to escape.  We have observed the dynamics of this sheet, as surface tension pulles it together, forming a vertical column of air, which often splits into two bubbles.  The resulting air bubbles are between 50-300 microns across.  This very small amount of air may become significant in some chemical processes, as well as for the very large number of drops in a typical rain storm, thus contributing to the transfer of air into lakes and the ocean.

The high-speed images on the right, show the contraction of the thin air sheet, taken with a novel ultra-high-speed camera developed by Profs. Etoh and Takehara.  The times are in micro-seconds and the scale bar is 500 micro-meters.

For more details, see Thoroddsen, S. T., Etoh, T. G. & Takehara, K., 2003, Air entrapment under and impacting drop.  J. Fluid Mech. Vol. 478, 125-134.