Cassie-Wenzel wetting transition on nanostructured superhydrophobic surfaces induced by surface acoustic waves

We report irreversible Cassie-Wenzel wetting transition on a nanostructured superhydrophobic surface employing surface acoustic wave (SAW) vibration. The transition is achieved upon penetration of the liquid into the nanogrooves driven by the inertial energy of the drop imparted by the SAW. However, the filling up of nanopores imposes an energy barrier (E b) to the transition, which requires the displacement of the initial solid-air interface inside the pores with a solid-liquid interface. We unravel that the relative magnitudes of the input acoustic energy (E a c), and this energy barrier, hence, dictate the occurrence of the wetting transition, with the irreversibility in the transition, therefore, being explained from energy minimization of the system following the transition. In addition, observing the dynamics of the wetting front allowed the different regimes of the wetting transition process to be identified.