Ice adhesion on superhydrophobic surfaces can significantly increase in humid environments because of frost nucleation within the textures. Here, we studied frost formation and ice adhesion on superhydrophobic surfaces with various surface morphologies using direct microscale imaging combined with macroscale adhesion tests. Whereas ice adhesion increases on microtextured surfaces, a 15-fold decrease is observed on nanotextured surfaces. This reduction is because of the inhibition of frost formation within the nanofeatures and the stabilization of vapor pockets. Such "Cassie ice"-promoting textures can be used in the design of anti-icing surfaces.
We describe the generation of mechanically robust superhydrophobic surfaces, which carry a hierarchical roughness that is composed of silicon microcones and silicon nanograss. Both micro and nanostructures were fabricated using mask-free dry etching processes. The microcones were obtained utilizing a cryogenic deep reactive ion etching (DRIE) process run in the overpassivation regime. By varying process parameters, surfaces with different microcones geometries and densities were achieved. The nanograss was fabricated using a modified DRIE process with alternating etching and passivation cycles ('BOSCH process'). All surfaces were covered with a layer of a fluorinated film so that superhydrophobic structures resulted. Depending on microcone geometry and density, the advancing contact angle ranged between 170° and 180°, and roll-off angles of 10 μL drops between 30' (0.5°) and 6° were observed. The samples were exposed to varying shear loads, and the changes in the morphology were recorded by using electron microscopy. The wetting angles of the mechanically challenged surfaces were recorded and correlated with the mechanical properties of the samples.
The nanostructures that are required to generate superhydrophobic surfaces are always sensitive to shear and are easily damaged, especially by scratching with sharp objects. As a result of this destruction, the water repellency will be lost. We introduce a novel approach to restoring the original surface properties after mechanical damage. In this approach, the damaged layer is shed like the skin of a snake. This is demonstrated with a three-layer stack as a proof-of-principle system: when the original, superhydrophobic surface layer is damaged, this leads to the dissolution of a sacrificial layer below it. Thus, the damaged layer is shed, a new unscathed surface is uncovered, and superhydrophobicity can easily be restored after a short washing.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.