Droplet spreading on a surface exhibiting solid-liquid interface premelting*

We study, using molecular-dynamics simulation, the spreading kinetics and equilibrium shape of liquid Pb droplets on an Al(111) substrate. The Al-Pb solid-liquid interface (SLI) was found previously to exhibit interfacial premelting at temperatures below the Al melting point [1]. We examine here how premelting affects the spreading and compare with both hydrodynamic (viscosity dominated) and kinetic (interfacial friction dominated) spreading mechanisms. For premelted surfaces, kinetic spreading is observed at intermediate times, in contrast to low temperatures near the Pb melting point where the surface is faceted and the hydrodynamic mechanism dominates. We conclude that the presence of the premelting layer has a significant effect on the thermodynamics of the Al(111)/Pb SLI and that the induced surface disorder gives rise to a kinetic spreading mechanism. We also observe that the structure of the droplet contact line with the premelted surface resembles that seen in reactive wetting.

[1] Y. Yang, M.D. Asta and B.B. Laird, Phys.Rev. Lett, 110, 096102 (2013)]