Wetting of a chemically heterogeneous surface

Theories for inhomogeneous fluids have focused in recent years on wetting, capillary condensation, and solvation forces for model systems where the surface(s) is (are) smooth homogeneous parallel plates, cylinders, or spherical drops. Unfortunately natural systems are more likely to be heterogeneous both in surface shape and surface chemistry. In this paper we discuss the consequences of chemical heterogeneity on wetting. Specifically, a two-dimensional (2D) implementation of a nonlocal density-functional theory is solved for a striped surface model. Both the strength and range of the heterogeneity are varied. Contact angles are calculated, and phase transitions (both the wetting transition and a local layering transition) are located. The wetting properties of the surface are shown to be strongly dependent on the nature of the surface heterogeneity. In addition highly ordered nanoscopic phases are found, and the operational limits for formation of ordered or crystalline phases of nanoscopic extent are discussed. (C) 1999 American Institute of Physics. [S0021-9606(99)70112-1].