Controllable Superhydrophobic Stainless Steel Surfaces Fabrication by Femtosecond Laser

Abstract Ultrafast laser processing has emerged as important tool for micro- and nanoscale fabrications. It is also used to create self-organized microstructures with nanoscale features on surfaces. Fabrications of superhydrophobic surfaces induced by femtosecond laser have many applications that include anticorrosion, self-cleaning, and drag reduction. We created hydrophobic surfaces on stainless steel surfaces by producing a hierarchical nano–microstructure with ultrafast laser ablation. Periodic nano–microstructures with different topographies were fabricated on stainless steel AISI 304 surface using a femtosecond laser with a pulse duration of 100 fs and a wavelength of 800 nm. Ablation was performed in the open air with no subsequent treatment. In this study, a three-level Box–Behnken design of response surface method was used to investigate and optimize the process parameters for hydrophobic surfaces. The laser-machined hierarchical nano–microstructures were examined using a scanning electron microscope and an opto-digital 3D microscope. The wetting of surfaces was measured in terms of the contact angle of a water droplet using a digitized goniometer. The contact angle of laser-modified surfaces was changed from a hydrophilic behavior to a hydrophobic one without any surface coatings. The effect of pulse energy was found to be significant on the output characterization. The results revealed that the average pulse energy range of 0.035–0.05 mJ at 10,000 Hz with a scanning speed of 10–100 mm/s and line separation of 10–30 μm produced hydrophobic surfaces with the apparent contact angle of 110–135°. We demonstrated a simple way to tune hydrophobicity using femtosecond laser surface modification in a single step with no subsequent post treatment.