The dynamics of liquid drops impacting superamphiphobic coatings is studied by high speed video microscopy. Superamphiphobic coatings repel water and oils. The coating consists of a fractal-like hydrophobized silica network. Mixtures of ethanol-water and glycerin-water are chosen to investigate the influence of interfacial tension and viscosity on spreading and retraction dynamics. At low impact velocity the drops completely rebound. However, the contact time increases with impact velocity, whereas the restitution coefficient decreases. We suggest that the drop partial impales the superamphiphobic coating. With increasing velocity the drops pin and an increasing amount of liquid remains in the coating. Drop retraction consists of a fast inertia-dominated phase followed by a slow decrease of the contact diameter. The crossover occurs when the diameter of the retracting drop matches the diameter of the drop before impact. From an estimate of the pressure is can be concluded that impalement is dominated by depinning rather than sagging.
schellen@mpip-mainz.mpg.de
