title: Wetting on the microscale: shape of a liquid drop on a microstructured surface at different length scales.
abstract: Describing wetting of a liquid on a rough or structured surface is a challenge because of the wide range of involved length scales. Nano- and micrometer-sized textures cause pinning of the contact line, reflected in a hysteresis of the contact angle. To investigate contact angles at different length scales, we imaged water drops on arrays of 5 μm high poly(dimethylsiloxane) micropillars. The drops were imaged by laser scanning confocal microscopy (LSCM), which allowed us to quantitatively analyze the local and large-scale drop profile simultaneously. Deviations of the shape of drops from a sphere decay at two different length scales. Close to the pillars, the amplitude of deviations decays exponentially within 1-2 μm. The drop profile approached a sphere at a length scale 1 order of magnitude larger than the pillars' height. The height and position dependence of the contact angles can be understood from the interplay of pinning of the contact line, the principal curvatures set by the topography of the substrate, and the minimization of the air-water interfaces.
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128, Mainz, Germany.
authors.forename: Periklis
authors.initials: P
authors.lastname: Papadopoulos
authors.forename: Xu
authors.initials: X
authors.lastname: Deng
authors.forename: Lena
authors.initials: L
authors.lastname: Mammen
authors.forename: Dirk-Michael
authors.initials: DM
authors.lastname: Drotlef
authors.forename: Glauco
authors.initials: G
authors.lastname: Battagliarin
authors.forename: Chen
authors.initials: C
authors.lastname: Li
authors.forename: Klaus
authors.initials: K
authors.lastname: Müllen
authors.forename: Katharina
authors.initials: K
authors.lastname: Landfester
authors.forename: Aranzazu
authors.initials: A
authors.lastname: del Campo
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Butt
authors.forename: Doris
authors.initials: D
authors.lastname: Vollmer