Thermally stable and durable superhydrophobic surfaces on stainless steel sheets with microholes via acid pretreatment and modification with self-assembled monolayers
Year: 2021
Journal: Microfluid. Nanofluid., Volume 25, NOV
Authors: Shaikh, Muhammad Omar; Yang, Jia-Yu; Chuang, Cheng-Hsin
In this study, we investigate the use of a facile two-step protocol to develop thermally stable and durable superhydrophobic (SH) surfaces on stainless steel (SS) that can strongly repel aqueous media. This involves pretreatment to achieve enhanced surface roughness using hydrofluoric acid etching followed by covalent modification with long-chain fluorosilanes which form a self-assembled monolayer (SAM) and reduce the surface energy of the SS. Experimental results show that hydrofluoric acid etching can increase the surface roughness and density of hydroxyl groups, thus enabling successful SAM adsorption. The SAM coating time, temperature and concentration have also been optimized to achieve dense and uniform coverage on the surface. It was observed that increasing the SAM concentration and temperature can effectively increase the interaction rate of SAM molecules with the S.S surface, thus resulting in a denser coverage and faster film formation rate. The proposed protocol in this study can successfully increase the hydrophobicity of the SS surface with an observed water contact angle as high as 170 degrees and no significant loss in performance after several months of manufacture and exposure to temperatures up to 300 degrees C. Furthermore, we have laser machined an array of microholes in SS sheets and have investigated the feasibility of our protocol to achieve IPX7 waterproof rating when the sheets are submerged at a depth of 1 m underwater for 30 min. It was observed that water did not penetrate through the microholes with a diameter of 10 mu m or less even at hydrostatic pressures of 1 m, thus highlighting the practical applicability of the proposed protocol to fabricate SH surfaces on SS for use in healthcare and industry.
