PANCAKE BOUNCING ON A SUPERHYDROPHOBIC SURFACE
Theory and simulations: Lisa Moevius and Julia Yeomans
Experiments: Yahua Liu and Zuankai Wang (City University of Hong Kong)
(Nature Physics 10 515 (2014))
Pancake bouncing occurs because fluid is pushed between the posts by the inertia of the falling drop. It is then rectified and pushed back out by the superhydrophobic posts. The drop bounces in a pancake shape if
- There is enough energy to lift the drop
- The fluid gets back to the surface approximately when the drop reaches its maximum extension.
Pancake bouncing occurs for many different post geometries. If the posts are
tapered (fatter at the bottom) it works particularly well. This is because the
horizontal fluid motion and the vertical fluid motion can both be modelled as
harmonic springs. Therefore the time scales for spreading and retraction are
independent of velocity and the right time scale balance is achieved over a
wide range of velocities. |
