Spreading and splashing of droplets impacting superhydrophobic substrates

A drop of radius R impacting a superhydrophobic substrate at a velocity V keeps its integrity and spreads over the solid for V<V_c or splashes, disintegrating into tiny droplets violently ejected radially outwards for V>V_c, with V_c the critical velocity for splashing. In contrast with the case of drop impact onto a hydrophilic substrate, Riboux & Gordillo [Phys. Rev. Lett. 113, 024507 (2014)], our experiments reveal that the critical condition for the splashing of water droplets impacting a hydrophobic substrate at normal atmospheric conditions is characterized by a value of the critical Weber number We_c=ρV_c²R/σ ≈70, far smaller than the one corresponding to the partially wetting case. Here we present a self consistent model, in very good agreement with experiments, capable to predict We_c as well as the full dynamics of the drop expansion and disintegration for We>We_c. In particular, our model is able to accurately predict the time evolution of the rim bordering the expanding lamella, R_t(T) as well as the radii R_d(T)«R and velocities V_d(T)»V of the small and fast droplets ejected when We>We_c.