Optimization of amphiphobic structural surface thickness in relation to its functionality on stainless steel plates

Fluorine-based amphiphobic coatings have been widely used in commercial textiles to provide water- and oil-repelling abilities. However, few reports from the literature survey have discussed the surface structural effects of the coated substrate on amphiphobicity. In this research, various thickness amphiphobic coatings based on mixed epoxy, tetraethylorthosilicate, and a particular alkoxysilane with fluorinated side chains (F-silane) were deposited on Grade 420 stainless steel plates. Film amphiphobicity is characterized by measuring the water and oil contact angles of the coating. Film morphology is examined using atomic force microscopy. The deposited films free of F-silane are thinner than 150 nm. The films become thick at high F-silane volume percentage with the surface cavities, ridges, and granules being masked out. On the addition of F-silane, the water contact angle of the deposited films increases up to 105° and then reaches a plateau of ∼ 107° with increasing F-silane. In contrast, the oil contact angle increases up to 60° at first and then slowly declines with the F-silane concentration. The total drop of oil contact angle by ∼ 20° was attributed to the masking out of surface features on film thickening. This indicates that the surface oleophobicity depends on surface structures. Therefore, improving surface amphiphobicity correlates with creating more refined multiscale surface structures during the industrial manufacturing process of steel plate, prior to surface modification by F-silane.