Engineering the wetting response of chromium thin films via femtosecond laser nanostructuring and environmental conditioning

This study investigates the temporal evolution of wettability on chromium surfaces structured with Laser-Induced Periodic Surface Structures (LIPSS) using a femtosecond pulsed laser. Two processing conditions, differing in scan track overlap, were selected to evaluate their influence on surface oxidation, roughness, and nanoparticle redeposition. The wetting behavior was analyzed over time through static contact angle measurements under different post-processing conditions, including samples left unwashed to retain nanoparticles and those washed to isolate the effect of the underlying surface. Additional experiments were performed using both a CO 2 stream during laser processing and an argon atmosphere during storage to evaluate the influence of environmental conditions on surface evolution. Unwashed samples exhibited a gradual increase in contact angle over time, reaching values above 120° after 240 hours, attributed to the adsorption of airborne carbonaceous contaminants facilitated by surface-deposited nanoparticles. In contrast, washed samples maintained low contact angles, revealing the key functional role of the nanoparticles in enabling hydrophobicity. Storage in an inert atmosphere slowed the hydrophobic transition by preserving the oxidation state induced during laser processing. These findings demonstrate the importance of controlling laser parameters, nanoparticle redeposition, and post-processing environment in tailoring the wetting behavior of laser-structured chromium surfaces.