Microscopic insight into surface wetting: relations between interfacial water structure and the underlying lattice constant.

We report simulation evidence that the structure of the first water layer next to the surface can strongly affect the contact angle of water droplets. Molecular dynamics simulations show that a small uniform strain (± 3%) applied to the lattice constant of a multilayer hydrophilic surface can introduce a marked change in the wetting tendency. In particular, when the lattice constant of a hydrophilic surface matches the projected oxygen-oxygen distance of bulk water to the surface, a contact-angle minimum is resulted. In stark contrast, such a lattice strain has little effect on the wetting properties of hydrophobic surfaces. The structure of the first water layer next to the hydrophilic surface gradually loses characteristics of liquid water when moving away from the contact-angle minimum. Our results demonstrate a close correlation among the length of lattice constant, contact angle of the water droplet, and the structure and dynamics of vicinal water.