(207d) Wetting Behavior of a Nanodroplet On a Heterogeneous Solid Surface

There is ample evidence in nature and laboratory experiments that modifying the topography of a solid surface can change its wettability. In this study, the wetting behavior of a sessile Lennard-Jones liquid droplet on a heterogeneous solid surface is investigated using molecular dynamics (MD) simulations. The solid surface is physically patterned with a periodic array of grooves embedded in an otherwise flat surface. Simulations of droplet spreading on the patterned surface show that the relative magnitudes of the length scales characterizing the surface heterogeneity compared to the drop size play an important role in determining the hydrophobic characteristics of the surface. The computed surface wettability phase diagram exhibits transitions between the Wenzel and Cassie modes of wetting as the step height, width and separation distance are varied. The transition between wetting modes is discussed through comparison of a simple model with the simulated results, as well as in terms of the interplay between the bulk liquid chemical potential, the liquid-solid interfacial tension, and the topology of the liquid-solid potential-energy surface induced by surface roughness.