Hypothesis: Although a lot of fluorinated coatings exhibit super-repellency to oils with low surface tensions, 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 nanospheres 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 condensation 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.
Keywords: Alcohol-repellency; Coating; Loss-free droplet manipulation; Microfluidics; Superomniphobicity.
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