Dynamic Wetting on Moving Surfaces: A Molecular Dynamics Study

We report molecular dynamics (MD) simulations of the dynamic wetting of nanoscale droplets on moving surfaces. The dynamic water contact angle and contact angle hysteresis are measured as a function of capillary number on smooth silicon and graphite surfaces. The hydrogen bonding and density profile variations are also reported, and the width of the water depletion layer is evaluated for droplets on three different static surfaces: silicon, graphite and a fictitious super-hydrophobic surface. Our results show that molecular displacements at the contact line are mostly influenced by interactions with the solid surface, while the viscous dissipation effects induced through the movement of surfaces are found to be negligible, especially for hydrophobic surfaces. This finding is in contrast with the wetting dynamics of macroscale droplets, which show significant dependence on the capillary number. This study may yield new insight into surface-wettability characteristics of nano droplets, in particular, developing new boundary conditions for continuum solvers for liquid flows in micro- and nanoscale devices.