(58c) The Effect of Nanoscale Chemical Heterogeneities On Wetting Behavior

Fluids at chemically heterogeneous surfaces display rich wetting behavior. Wetting layers on such surfaces adopt a variety of morphologies and morphological transitions are commonplace in these systems. The importance of understanding interfacial fluid behavior at surfaces with chemical heterogeneities in the nanoscale regime has increased considerably in the last decade or so, due to progress made in printing specified energetic patterns on a surface at very small length scales. Natural systems, such as assemblies of amphiphilic molecules and proteins, also provide examples of relevant nanoscale chemically heterogeneous surfaces. In this presentation, we provide results from a study aimed at understanding the wetting behavior of fluids at striped nanopatterned surfaces. Fluids at striped nanopatterned surfaces (characteristic stripe length scales of say 5-20 fluid diameters) are known to exhibit complex surface phase behavior, including a transition between a homogeneous vapor and a "fluid stripe" morphology characterized by thin fluid layers (3-5 fluid diameter thickness) over the high energy stripe surrounded by a vapor.  Such systems are also associated with an "unbending" transition in which the aforementioned fluid stripe morphology transforms into a uniform wetting layer.  We report on a Lennard-Jones system characterized by a regular one-dimensional heterogeneity. Each period contains atomistically-detailed "A" and "B" surface regions.  We investigate how the periodicity, energy asymmetry, and surface coverage of these stripes influence the surface phase behavior. Overall, we find that modest variation of these parameters leads to significant changes in the macroscopic wetting behavior.