Abstract:

We have carried out an experimental study of liquid drop impact on superhydrophobic substrates covered by a carpet of chemically coated nano-wires. The micro-structure of the surface is similar to some biological ones (Lotus leaf for example). In this situation the contact angle can then be considered as equal to 180 degrees, with no hysteresis. Due to its initial inertia, the drop experiences a flattening phase after it hits the surface, taking the shape of a pancake. Once it reaches its maximal lateral extension, the drop begins to retract and bounces back. We have extracted the lateral extension of the drop, and we propose a model that explains the trend. We find a limit initial velocity beyond which the drop protrudes into the nano-wire carpet. We discuss the relevance of practical issues in terms of self-cleaning surfaces or spray-cooling.

Key words: superhydrophobic surfaces, drop impact