Wehavecarriedoutanexperimentalstudyofliquiddropimpactonsuperhydrophobicsubstratescoveredbyacarpetofchemicallycoatednano-wires.Themicro-structureofthesurfaceissimilartosomebiologicalones(Lotusleafforexample).Inthissituationthecontactanglecanthenbeconsideredasequalto180degrees,withnohysteresis.Duetoitsinitialinertia,thedropexperiencesaflatteningphaseafterithitsthesurface,takingtheshapeofapancake.Onceitreachesitsmaximallateralextension,thedropbeginstoretractandbouncesback.Wehaveextractedthelateralextensionofthedrop,andweproposeamodelthatexplainsthetrend.Wefindalimitinitialvelocitybeyondwhichthedropprotrudesintothenano-wirecarpet.Wediscusstherelevanceofpracticalissuesintermsofself-cleaningsurfacesorspray-cooling.
