Super-alcohol-repellent coatings

Hypothesis: Although a lot of fluorinated coatings exhibit super-repellency to oils with low surface ten-sions, most of them are readily wetted by alcohols with high surface tensions, wherein the un-crosslinked fluorinated silane is expected to result in the failure of alcohol-repellency. Hence, the coating could be super-repellent to alcohols if the fluorinated silane is fully crosslinked by annealing. Experiments: We fabricate the super-alcohol-repellent coating via covering sintered hollow silica nano-spheres with perfluoroalkyl silane, followed by a simple two-step annealing. The surface chemistry of the coating is further examined by X-ray photoelectron spectroscopy. Findings: The super-alcohol-repellent coating is remarkably super-repellent to diverse alcohols of surface tension from 20.9 to 64.8 mN m(-1) and thus enables loss-free manipulation of alcohol droplets for amino acid detection. More importantly, we reveal that the annealing procedure could promote the condensa-tion of silanol groups, showing the key role played by heat-mediated crosslinking of perfluoroalkyl silane in preparing alcohol-repellent coatings. Such annealing strategy is also proved to be effective for other fluorinated coatings to achieve super alcohol-repellency. Together with its super-repellency to virtually all liquids, the coating enables loss-free processing of diverse liquids, thus being of significant value for biological, chemical and medical applications. (C) 2022 Elsevier Inc. All rights reserved.