2 research outputs found
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 AlÂ(III) ions etched off by OH<sup>–</sup> can be transformed to a bayerite array growing out of the Al substrate
with the help of CO<sub>2</sub> 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