Hydrophobic and Hydrophilic Surfaces Created by Nanosecond

Steel and aluminum test panels were irradiated with large numbers of pulses from a Nd:YAG (532 nm) or KrF excimer (248 nm) at fluence between 0.3 and 3.0 J/cm2, which induced changes to the surface topography of the panels. In most cases this led to considerable roughening of the surface, and decoration of the roughened surface with nanoscale particles. The contact angle of water droplets was measured, and showed both increased and decreased contact angle compared to unshot material, depending on the laser conditions. The changes to the surface hydrophobicity are non-monotonic in both laser fluence and shot density. Comparisons against surface topography suggest that the surfaces that exhibit two length scales of roughness are more likely to be excessively hydrophobic, whereas surfaces that have large scale features are more likely to be excessively hydrophilic.