Spreading Dynamics of Water Droplets on a Completely Wetting Surface

S Bekele and OG Evans and M Tsige, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 20109-20115 (2020).

DOI: 10.1021/acs.jpcc.0c05167

The spreading of water droplets of varying sizes on a completely wetting surface where the kinetics of spreading are controlled by hydrogen bonding between substrate and water molecules is modeled for the first time using atomistic molecular dynamics simulations. 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. The bulk part of the droplet initially spreads over the monolayer with increasing radius until a characteristic time t*. Beyond t*, it shrinks while maintaining a constant contact angle and, interestingly, the radius is described well with a first-principles model based on hydrodynamic theory. Overall, the simulation results qualitatively agree with recent experimental data.

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