Terraced spreading of simple liquids on solid surfaces

We have studied the spreading of liquid drops on a solid surface by molecular-dynamics simulations of coexisting three-phase Lennard-Jones systems of liquid, vapor, and solid. We consider both spherically symmetric atoms and diatomic molecules, and a range of interaction strengths. As the attraction between liquid and solid increases we observe a smooth transition in spreading regimes, from partial to complete to terraced wetting. In the terraced case, where distinct monomolecular layers spread with different velocities, the layers are ordered but not solid, with substantial molecular diffusion both within and between layers. The qualitative behavior resembles recent experimental findings, but the detailed dynamics differ. In particular, the layers exhibit an unusual spreading law, where their radii vary in time as ${\mathit{R}}^2$∼${\log }_{10}$t, which disagrees with experiments on polymeric liquids as well as recent calculations.