Wetting Transitions in Polymer Nanograss Generated by Nanoimprinting

To study the transitions between wetting regimes on highly rough surfaces, the authors have fabricated a set of polymer nanograss surfaces with virtually identical geometry, but different surface chemistry by double replication. A common silicon master of the “black silicon” type, obtained by cryogenic SF6/O2 plasma etching, is used for all replications. Additionally, the same process is used to generate nanograss-carrying, transferrable foils, and the authors show how to increase sample size by multiple lithography steps side by side on one support. This process proves generally applicable to soluble thermoplastics. Thus, by choosing polymers with different surface energy, all three possible wetting regimes on highly rough surfaces are realized—superwetting, superhydrophobicity, and the intermediate, sticky Wenzel regime. The locations of and the phenomena close to the transitions between these three wetting regimes are studied, based on dynamic contact angle measurements.