Laser texturing of stainless steel under different processing atmospheres: From superhydrophilic to superhydrophobic surfaces

Wettability plays a major role in a variety of surface related phenomena, as corrosion, heat transfer or tissue adhesion on implants. Consequently, great research effort is being devoted to control the wetting degree of functional surfaces. Pulsed laser texturing at micro/nanometric level has been widely used for that purpose as a precision/time efficient technique. This work studies the role of the processing atmosphere in controlling the wettability of commercial AISI 304 by laser texturing. A pulsed laser source (lambda = 532 nm) working at the nanosecond regime was employed and five different atmospheres were tested (i. e. O-2, Air, CO2, N-2, Ar). The results show clear differences in the wetting behaviour depending solely on the processing environment, ranging from hydrophilicity (31 degrees) to hydrophobicity (125 degrees). Those differences in wettability were found to be a consequence of changes in surface chemistry between samples processed under the various gases. The laser processing parameters showed a capability to tune the final wetting behaviour by controlling the topography and modulating the chemical composition given by the processing environment. It is demonstrated how the effects of the atmosphere can be exploited to tailor the wettability of the untreated surfaces (theta = 88 degrees) up to the desired value, ranging from superhydrophilicity (theta = 0 degrees) to superhydrophobicity (theta = 152 degrees).