Photo-switching between the zwitterionic and anionic forms of a photoacid allows reversible hydrophobization and assembly of cationic gold nanoparticles.

Accurate wetting characterization is crucial for the development of next-generation superhydrophobic surfaces. Traditionally, wetting properties are measured with a contact angle goniometer (CAG) suitable for a broad range of surfaces. However, due to optical errors and challenges in baseline positioning, the CAG method suffers from inaccuracies on superhydrophobic surfaces. Here we present an improved version of the oscillating droplet tribometer (ODT), which can reliably assess wetting properties on superhydrophobic surfaces by measuring the frictional forces of a water-based ferrofluid droplet oscillating in a magnetic field. We demonstrate that ODT has superior accuracy compared to CAG by measuring the wetting properties of four different superhydrophobic surfaces (commercial Glaco and Hydrobead coatings, black silicon coated with fluoropolymer, and nanostructured copper modified with lauric acid). We show that ODT can detect the small but significant changes in wetting properties caused by the thermal restructuring of surfaces that are undetectable by CAG. Even more, unlike any other wetting characterization technique, ODT features an inverse sensitivity: the more repellent the surface, the lower the error of measurement, which was demonstrated by experiments and simulations.

Super‐liquid‐repellent surfaces feature high liquid contact angles and low sliding angles find key applications in anti‐fouling and self‐cleaning. While repellency for water is easily achieved with hydrocarbon functionalities, repellency for many low‐surface‐tension liquids (down to 30 mN m−1) still requires perfluoroalkyls (a persistent environmental pollutant and bioaccumulation hazard). Here, the scalable room‐temperature synthesis of stochastic nanoparticle surfaces with fluoro‐free moieties is investigated. Silicone (dimethyl and monomethyl) and hydrocarbon surface chemistries are benchmarked against perfluoroalkyls, assessed using model low‐surface‐tension liquids (ethanol–water mixtures). It is discovered that both hydrocarbon‐ and dimethyl‐silicone‐based functionalization can achieve super‐liquid‐repellency down to 40–41 mN m−1 and 32–33 mN m−1, respectively (vs 27–32 mN m−1 for perfluoroalkyls). The dimethyl silicone variant demonstrates superior fluoro‐free liquid repellency likely due to its denser dimethyl molecular configuration. It is shown that perfluoroalkyls are not necessary for many real‐world scenarios requiring super‐liquid‐repellency. Effective super‐repellency of different surface chemistries against different liquids can be adequately predicted using empirically verified phase diagrams. These findings encourage a liquid‐centric design, i.e., tailoring surfaces for target liquid properties. Herein, key guidelines are provided for achieving functional yet sustainably designed super‐liquid‐repellency.

Gas vesicles used as contrast agents for noninvasive ultrasound imaging must be formulated to be stable, and their mechanical properties must be assessed. We report here the formation of perfluoro- n -butane microbubbles coated with surface-active proteins that are produced by filamentous fungi (hydrophobin HFBI from Trichoderma reesei ). Using pendant drop and pipette aspiration techniques, we show that these giant gas vesicles behave like glassy polymersomes, and we discover novel gas extraction regimes. We develop a model to analyze the micropipette aspiration of these compressible gas vesicles and compare them to incompressible liquid-filled vesicles. We introduce a sealing parameter to characterize the leakage of gas under aspiration through the pores of the protein coating. Utilizing this model, we can determine the elastic dilatation modulus, surface viscosity, and porosity of the membrane. These results demonstrate the engineering potential of protein-coated bubbles for echogenic and therapeutic applications and extend the use of the pipette aspiration technique to compressible and porous systems.

Inside Front Cover: The cover image is based on the Research Article Oscillating droplet tribometer for sensitive and reliable wetting characterization of superhydrophobic surfaces by Junaid et al.