Fabrication of durable superhydrophobic stainless steel via two-step chemical etching and fluorosilane coating

Abstract

Stainless steel surfaces with durable superhydrophobicity are highly desirable for diverse industrial applications; however, achieving both superhydrophobicity and long-term durability remains challenging owing to the vulnerability of surface coatings to mechanical damage and chemical degradation. This study addresses this challenge by fabricating a durable superhydrophobic surface on 316 stainless steel (316SS) using a cost-effective, scalable, two-step wet-chemical etching process, followed by heptadecafluoro-1,1,2,2-tetrahydrodecyl trichlorosilane (HDFS) coating. The 316SS substrates were etched in nitric acid for 30 min and then in ferric chloride solution for various durations to create hierarchical micro-nano structures. The surface properties were characterized using SEM, XPS, and water contact angle measurements. The mechanical and chemical durability were evaluated using various tests. The optimal etching time in ferric chloride was 30 min, resulting in the highest surface roughness, most stable superhydrophobicity (WCA ∼150°, sliding angle <10°), and best durability. The improved durability was attributed to the robust micro-nano structure that stabilized the HDFS coating and protected the substrate. This work demonstrates an effective approach for fabricating durable superhydrophobic surfaces on stainless steels with superior resistance to physical and chemical degradation, revealing the relationship between surface morphology, wettability, and durability, which advances the development of protective coatings for stainless steel in harsh environments.