Eco-Friendly Fabrication of Superhydrophobic Bayerite Array on Al Foil via an Etching and Growth Process

In this work, we present a clean and atom-economic fabrication of superhydrophobic Al surfaces, where the Al­(III) ions etched off by OH^– can be transformed to a bayerite array growing out of the Al substrate with the help of CO₂ in air. The resultant array is composed of bayerite microneedles with nanosteps on their surfaces, exhibiting binary micro/nanostructures. The formation mechanism of the microneedles follows a fast etching and subsequent kinetic growth route, significantly different from the traditional etching route. After the chemisorption of steric acid, the resultant Al surface shows a water contact angle of 167° and a sliding angle of ∼3° for a 5 μL water droplet. The dual-scale roughness together with the low surface energy of stearic acid accounts for the superhydrophobicity. The resultant Al surface has an anticorrosion against electrolyte solution and robust repellence against acidic or alkali droplets. It also maintains hydrophobicity after ultrasonication treatment

Studying the impact of the pre-exponential factor on templated nucleation

Traditionally, the enhancement of nucleation rates in the presence of heterogeneous surfaces in crystallisation processes has been attributed to the modification of the interfacial energy of the system according to the classical nucleation theory. However, recent developments have shown that heterogeneous surfaces instead alter the pre-exponential factor of nucleation. In this work, the nucleation kinetics of glycine and diglycine in aqueous solutions have been explored in the presence and absence of a heterogeneous surface. Results from induction time experiments show that the presence of a heterogeneous surface increases the pre-exponential factor by 2-fold or more for both glycine and diglycine, while the interfacial energy remains unchanged for both species. This study suggests that the heterogeneous surface enhances the nucleation rate via hydrogen bond formation with both glycine and diglycine. This is verified by hydrogen bond propensity calculations, molecular functionality analysis, and calculation of the time taken for a solute molecule to attach to the growing nucleus, which is an order of magnitude shorter than the estimated lifetime of the hydrogen bond. The effect of the heterosurface is of greater magnitude for diglycine than for glycine, which may be due to the heightened molecular complementarity between the hydrogen bond donor and acceptor sites on diglycine and the heterosurface</p