Dynamical response of an aqueous nanodrop with the underlying substrate of varying wettability.

The wetting kinetics of a water nanodrop is explored on switchable hydrophilic-hydrophobic surfaces placed on top of a bilayer gold surface using molecular dynamics simulations. The contact angle is altered by modifying the energy of interaction of the underlying substrate atoms with the aqueous drop. Analysis based on the calculation of time correlation function shows that the drop relaxes faster in case of hydrophobic surface in comparison to hydrophilic surface. This faster relaxation is explained on the basis of frictional force developed due to perimeter motion of the liquid molecules. Friction coefficients derived from continuum hydrodynamic (HD) theory and on the basis of molecular kinetic theory (MKT), manifests the predominance of liquid-substrate friction. The present work establishes a relation among various process monitoring parameters to govern the wettability of a liquid nanodroplet on a solid substrate. This concept can be explored to design miniaturized optical devices.