Inducing hydrophobicity in Stainless Steel 304 by mechanical texturing and chemical functionalization

Abstract This study investigates the impact of combined texturing by micromachining and chemical functionalization on the wetting behavior and water condensation of a metallic surface. The transition from the Wenzel to Cassie-Baxter or impregnated Cassie-Baxter regimes was unveiled. Initially, grooved stainless steel 304 specimens displayed hydrophobic wetting in the Wenzel mode. The chemical functionalization with silane triggered a remarkable shift that was not observed in non-textured by micromachining samples. Thus contact angles surged, facilitating a transition to the Cassie-Baxter state for directional canal specimens and the impregnated Cassie-Baxter state for those with pyramidal patterns. Roll-off angle experiments showcased distinct behavior among specimens featuring canals or pyramidal structures. Specimens with canals exhibited notably lower roll-off angles compared to both flat surfaces and those with pyramidal patterns. Notably, the orientation of canals influenced these angles, with vertically aligned canals demonstrating reduced roll-off angles. In humid environments, micro-machined surfaces exhibited superior water condensation capabilities compared to untreated flat SS304 surfaces. Remarkably, chemically functionalized grooved specimens presented larger condensate droplet diameters than flat surfaces. Consequently a remarkable enhancement in water condensation and a 7 fold higher latent heat transfer coefficient is reported.