Coating is an essential step in adjusting the surface properties of materials. Superhydrophobic coatings with contact angles greater than 150° and roll-off angles below 10° for water have been developed, based on low-energy surfaces and roughness on the nano- and micrometer scales. However, these surfaces are still wetted by organic liquids such as surfactant-based solutions, alcohols, or alkanes. Coatings that are simultaneously superhydrophobic and superoleophobic are rare. We designed an easily fabricated, transparent, and oil-rebounding superamphiphobic coating. A porous deposit of candle soot was coated with a 25-nanometer-thick silica shell. The black coating became transparent after calcination at 600°C. After silanization, the coating was superamphiphobic and remained so even after its top layer was damaged by sand impingement.

A droplet deposited or impacting on a superhydrophobic surface rolls off easily, leaving the surface dry and clean. This remarkable property is due to a surface structure that favors the entrainment of air cushions beneath the drop, leading to the so-called Cassie state. The Cassie state competes with the Wenzel (impaled) state, in which the liquid fully wets the substrate. To use superhydrophobicity, impalement of the drop into the surface structure needs to be prevented. To understand the underlying processes, we image the impalement dynamics in three dimensions by confocal microscopy. While the drop evaporates from a pillar array, its rim recedes via stepwise depinning from the edge of the pillars. Before depinning, finger-like necks form due to adhesion of the drop at the pillar's circumference. Once the pressure becomes too high, or the drop too small, the drop slowly impales the texture. The thickness of the air cushion decreases gradually. As soon as the water-air interface touches the substrate, complete wetting proceeds within milliseconds. This visualization of the impalement dynamics will facilitate the development and characterization of superhydrophobic surfaces.micropillars | pinning | wetting transition | contact angle | lithography | self-cleaning | hysteresis

Robust transparent superhydrophobic coatings are advantage for convenient and cost‐effective maintenance of a variety of surfaces. Until today most coatings suffer from poor mechanical stability. Based on porous silica capsules we developed an easy to apply method to overcome these limitations. The coating is not only mechanically robust but also highly transparent as demonstrated by applying it to organic solar cells, keeping its high‐performance unaltered.

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.

Surface roughness on different length scales is favourable for superhydrophobic behaviour of surfaces. Here we report (i) an improved synthesis for hybrid raspberry-like particles and (ii) a novel method to obtain superhydrophobic films of good mechanical stability. Polystyrene spheres with a diameter of 400 nm-1 microm are decorated with silica colloids < 100 nm in size, thus introducing surface asperities on a second length scale. To improve mechanical resistance, we then coated the polystyrene core and attached silica colloids with a smooth silica shell of 10 nm to 40 nm thickness. All three steps of this synthesis procedure can be sensitively tuned so that the average size and number of the silica colloids as well as the morphology of the resulting raspberry particles can be predicted. As the particles disperse in water, either monolayers can be prepared by dip coating or multilayers by drop casting. Although mechanically stable, the shells are porous enough to allow for leakage of molten or dissolved polystyrene from the core. In tetrahydrofuran vapour polystyrene bridges form between the particles that render the multilayer-film stable. Leaked polystyrene that masks some asperities can be removed by plasma cleaning. Surface roughness on larger scales can be tuned by the drying procedure. The films are hydrophobized by silanization with a semi-fluorinate silane.