Impacting Drops
Drops Skating and Bouncing Off Surfaces

Inspired by the theoretical predictions of Brenner and Mahadevan (top), Rubinstein has made a high-speed 3D measurement of the nanometer thin film of air separating an impacting drop of water from a hydrophilic glass surface. The actual point of contact between the drop and the surface begins to nucleate after 46 microseconds, and ultimately leads to perfect wetting of the surface. When nucleation of the contact is suppressed, wetting does not occur and the drop of water can bounce right off a hydrophilic surface (bottom). Montage of fast camera images taken from the side (top) and with Total Internal Reflection (TIR) Microscopy (bottom) of two identical experiments. Frames i-iii are taken in intervals of 1.8msec; frame iv is taken 6.5msec after the first frame.