Iso- to anisotropic wetting on microwrinkled surfaces with varying intrinsic wettability

We examine the combined effects of topography and intrinsic material wettability on the overall wetting behaviour of patterned surfaces, with widespread practical applications. While the presence of surface microwrinkles is well-known to induce anisotropic wetting, we experimentally map the relation between the degree of anisotropy and the intrinsic wettability of the surface. We employ one-dimensional (1D) wrinkling of polydimethylsiloxane (PDMS) elastomers, with tuneable periodicity and amplitude, and separately vary the intrinsic contact angle by controlled surface oxidation and hydrophobic recovery. We demonstrate the importance of the interplay between topography and intrinsic wetting by switching the spontaneous, gravity-driven droplet motion on vertically inclined representative surfaces. We describe our findings with a minimal model that estimates the threshold volume necessary for the droplet mobility on a vertically inclined surface. These findings provide a framework for designing surfaces that support the passive, self-cleaning of functional coatings.