(358c) Spreading Dynamics of a Nanodroplet on a Physically-Patterned Solid Surface

Spreading dynamics of a sessile Lennard-Jones liquid droplet on a physically-patterned solid surface are studied using molecular dynamics (MD) simulation. The solid surface is physically patterned with a set of steps embedded on an otherwise flat surface. To speed up computation of liquid-solid interactions, a modified Steele potential accounting for arrays of steps with the desired roughness and solid fraction is derived and used in the computations. Spreading dynamics of larger two-dimensional droplets are also examined. Simulation results show that the wetting behavior of nanodroplets is not only dependent on the solid surface energy, but is also affected by the heterogeneity of the solid surface. For fixed surface energy of the solid, the topographic structure of the solid surface can significantly affect its hydrophobic characteristics. By varying the step height and separation distance, a transition between the Wenzel and Cassie modes of wetting is observed in the simulations. These observations are explained in terms of the interplay between the bulk liquid chemical potential and the liquid-solid interfacial tension, as well as the topology of the liquid-solid potential-energy surface induced by surface heterogeneity.