Fabrication of Superhydrophobic Stainless-Steel Surfaces via Two-step Chemical Etching and Surface Functionalization and their Durability Assessment

Abstract

Superhydrophobic stainless-steel surfaces were fabricated using two-step chemical etching followed by surface functionalization with perfluorodecyltrichlorosilane (FDTS). The SUS 304 stainless-steel specimens underwent primary etching in hydrofluoric acid (HF) for different durations (60-1800 s), followed by secondary etching in nitric acid for 30 min. The etched surfaces were modified with FDTS to form self-assembled mono layers. Surface morphology analysis of the specimens revealed progressive roughening with increasing HF etch ing time, with roughness values increasing from 0.15 (bare) to 0.56 μm (1500 s) following etching. Water contact angle measurements of the specimens demonstrated a transformation from hydrophilic behavior (22.01o) after etching to superhydrophobic behavior (156.40o) after applying the FDTS coating to the specimen etched for 1500 s. The sliding angles of the specimens etched for 1200 s or longer were all below 1o, indicating the formation of a stable Cassie-Baxter state. Mechanical durability tests conducted on the specimens showed that the textured 1500-s specimen retained its superhydrophobic properties after five scratch cycles, with a water contact angle > 150o, while the bare specimen had its water contact angle decreasing from 125.34o to 113.43o at the end of the five scratch cycles. The hierarchical surface structures created via two-step etching provided the coatings with mechanical protection and self-cleaning abilities. The optimal etching duration of 1500 s balanced the sur face roughness, hydrophobic performance, and processing efficiency of the specimens. Thus, this study demon strates a scalable approach for producing durable superhydrophobic stainless-steel surfaces with water repellency and self-cleaning properties, suitable for industrial applications