Understanding the Nature of Nanoscale Wetting through All-atom Simulations

Wetting plays an important role in many areas of science and engineering, including adhesion, corrosion, and ice formation among others. While macroscale wetting is well understood, a sufficient characterization of nanoscale wetting remains to be developed. Since the experimental limit of droplet spreading is presently on the order of seconds and micrometers, we turn to all-atom molecular dynamics simulations to study this phenomenon on the nanoscale. We focus our attention to simulations of pure water on atomically flat substrates such as sapphire and quartz, in which we observe significant qualitative deviations from macroscale wetting dynamics. In particular, we observe the formation of a one-molecule-thick ``monolayer'' which spreads significantly faster than the bulk of the droplet. Our interest lies in the relationship between the radius of the monolayer and other features of the droplet such as bulk radius, contact angle, and droplet height over time in both spherical and cylindrical droplets. Using a combination of first principles and constitutive relationships, we construct and analyze a model for the observed behavior in order to explain the causes and implications of the unique dynamics of wetting at this scale.