Micro/Nanobinary Structure of Silver Films on Copper Alloys with Stable Water-Repellent Property under Dynamic Conditions

Facile galvanic replacement was adopted to grow cauliflower-like and dendrite coral-like silver films on commercial copper alloy substrates. Both types of silver films possess micro/nanobinary structures, the formation and evolution of which are achieved through the oriented attachment growth mechanism. After modification by a monolayer of n-dodecanethiol, the cauliflower-like silver film becomes hydrophobic with a contact angle (CA) of 115 ± 1° and a CA hysteresis of 74 ± 1° and the dendrite coral-like silver film exhibits the extreme hydrophobicity characterized by a CA of 158 ± 1° and a CA hysteresis of less than 2 ± 1°. Furthermore, the bouncing property of millimeter-sized water droplets on the modified dendrite coral-like silver surface is much better than that on the modified cauliflower-like silver surface. The different wetting property between the two silver films is attributed to the surface roughness. Larger surface roughness provided by the dendrite coral-like silver film means more air pockets, among the micro/nanobinary structures, that bounce water droplets back more strongly. The dynamic bouncing behavior of water droplets, such as restitution coefficient and contact time, on the superhydrophobic modified cauliflower-like silver surface was also investigated at different impact velocities.