Molecular dynamics investigation into the spreading of water on completely wetting surfaces

The spreading of water droplets of varying sizes on a completely wetting surface is modeled for the first time using atomistic molecular dynamics simulations. In the early stage of droplet spreading, the inertia of the drop resists the capillary driven motion and in the final stages, the effect of viscous forces acting in the neighborhood of the three-phase contact line become relevant and the competition between surface tension and viscous forces results in extremely slow spreading dynamics. The spreading observed is characterized by the bulk part of a droplet spreading over a high-density monolayer of water that forms within tens of picoseconds after the droplet is placed on the surface. The monolayer exhibits two spreading regimes, each following a power law in time with different exponents, and the late stage is faster than that predicted by Tanner’s law. We will show that a first principle model based on hydrodynamic theory describes the spreading data rather well in the regime where the low contact angle approximation holds and, overall, the simulation results qualitatively agree with recent experimental data.