Impact of liquid droplets on a spinning disk

We study the impact of a water droplet at the center of a spinning disk whose surface is covered by soot to create a superhydrophobic substrate. By varying the velocity of impact V and the rotation rate w, we observe a rich variety of dynamics including bouncing, spreading and dewetting. For low values of V and w, the drops bounce while for intermediate speeds the drops spread on the substrate, retract and then break-up into smaller droplets. For larger values of both V and w, the drops dewet via the nucleation of a dry spot at the center of the spreading liquid sheet. We provide an ``impact'' diagram that summarizes our experimental observations, and rationalize these results using simple physical arguments comparing the surface tension effects with rotation-driven spreading and thinning.