Water Micro-Wettability Evaluation of Several Metal Surfaces by Atomic Force Microscopy

The distilled water macro- and micro-wetting morphologies on wet-polished, air-oxidized and distilled-water-immersed pure chromium, nickel, iron and SUS304 steel surfaces were observed with a digital microscope or an AC non-contact mode of atomic force microscope. The macro- and micro-wettabilities were measured from the obtained morphologies, and the relationship between them was examined. The influence of the surface chemical state on wettability was also examined.Sample surface layers comprised pure metals (nickel, chromium or iron) and their oxides and hydroxides, and organic contaminants. Wettabilities differed for pure chromium, nickel, iron and SUS304 steel. Micro-wettability was higher than macro-wettability for all samples, but the dispersion of micro-wettabilities was large. Wettability was also dependent on different surface treatments such as wet polishing, air oxidation and water immersion.