Scaling of wetting and prewetting transitions on nanopatterned walls

We consider a nanopatterned planar wall consisting of a periodic array of stripes of width L, which are completely wet by liquid (contact angle (theta = 0), separated by regions of width D which are completely dry (contact angle (theta = pi ). Using microscopic density functional theory, we show that, in the presence of long-ranged dispersion forces, the wall-gas interface undergoes a first-order wetting transition, at bulk coexistence as the separation D is reduced to a value D-omega alpha In L, induced by the bridging between neighboring liquid droplets. Associated with this is a line of prewetting transitions occurring off coexistence. By varying the stripe width L, we show that the prewetting line shows universal scaling behavior and data collapse. This verifies predictions based on mesoscopic models for the scaling properties associated with finite-size effects at complete wetting including the logarithmic singular contribution to the surface free energy.