(429d) Wetting of Nanopatterned Solid Surfaces

It is well recognized that the chemical composition and topographic structure of a solid surface strongly influence the wetting properties of the surface. The wettability of patterned surfaces is typically classified by either the Wenzel mode, in which liquid droplets are in full contact with the solid substrate, the Cassie mode, in which the liquid is evacuated from recessed areas of the pattern, or a mixed mode with characteristics of both modes. In this work, we use molecular dynamics (MD) simulations, in conjunction with a novel Patterned Surface Potential for describing liquid-solid interactions, to study wetting transitions on patterned surfaces. We study wetting on surfaces patterned with rectangular grooves, as well as with cylindrical pillars. The wetting transitions in these systems depend on the parameters characterizing the surface topology. For example, at constant height and width of the rectangular grooves, the observed wetting mode depends on the groove separation. Simulations for different surface topologies and drop sizes are carried out to construct wettability phase diagrams. Our results match experimental trends. By scaling the topological parameters of the surface patterns by droplet size, we find that the critical topological parameters associated with wetting transitions become independent of droplet size for sufficiently large drops. When the critical topological parameters are scaled by droplet radius, our predicted wetting transitions are in good agreement with results for an analogous experimental system. Thus, our results indicate that MD simulations can be used to probe wetting over length scales ranging from nanoscopic to macroscopic.