Molecular dynamics simulations of nanodroplet spreading on solid surfaces, effect of droplet size

Molecular dynamics simulations were performed to study the spreading characteristics of nano-sized droplets on solid surfaces. The spreading behavior was analyzed in terms of the temporal evolution of the dynamic contact angle and spreading diameter for wettable, partially wettable and non-wettable surfaces. The computational model was validated through qualitative comparison with the measurements of Bayer and Megaridis, and through comparison with existing correlations. The comparison based on the ratio of relevant time scales indicated that for the conditions investigated, the spreading dynamics is governed by inertial and surface forces, with negligible influence of viscous forces. In addition, the simulation results indicated that the dynamic contact angle and spreading diameter, as well as the advancing and receding time periods, exhibit strong dependence on droplet size. These results were further analyzed to obtain correlations for the effect of droplet size on these spreading parameters. The correlations indicated that the normalized spreading diameter and contact angle scale with drop diameter as D-m/D-0 alpha D-0(0.5) and theta(R) alpha D-0(0.5), while the advancing and receding time periods scale as t alpha D-0(2/3) Global kinetic energy and surface energy considerations were used to provide a physical basis for these correlations. The correlations were also found to be generally consistent with the experimentally observed spreading behavior of macroscopic droplets.