Wetting state transition of water droplet on graphene surface with nanoscale pillars

The regulation of solid surface wettability can be effectively achieved by controlling surface microstructure and external
electric fields. Here, the wetting properties of graphene textured with nanoscale square, circular and cone pillars are systematically investigated by using molecular dynamics simulation. It is shown that the transition of water droplet located on periodic pillars from Wenzel state to Cassie state is highly sensitive to the height of pillars and the hydrophilic-to-hydrophobic switch is achievable by decreasing the inter-pillar spacing. In addition, the behaviors of water droplets situated on graphene under external electric fields are also discussed. The configuration of water droplet performs a hemispherical-conical-ordered cylindrical shape variation with the increase of external electric fields. Notably, the orientations of water dipoles experience remarkable change from disorder to order in the process of increasing electric fields due to the polarization of water molecules induced by static electric fields. These findings could shed some light on future applications of graphene-based devices with controllable wettability.