In this work, we have used a nanosecond pulsed fiber laser to modify the wettability characteristics of AISI 430 steel. For this, various surface morphologies were created on the samples by laser irradiation with different overlapping and intensity parameters. Immediately upon laser treatment, all the structured samples acquired either hydrophilic or superhydrophilic wetting angles. All the samples were also analyzed with XRD. Then, laser-treated samples were kept in ambient air and/or low-temperature annealing was applied to reach hydrophobic surface properties. Interestingly, these surfaces returned back practically to their initial wetting state by cleaning in an ultrasonic bath. The obtained results are analyzed based on the existing wettability models.

Broad tunability of water wetting angle on an AISI 304 steel surface was demonstrated by 1064 nm, 100 ns laser ablative nano-and micro-texturing in the air at different incident fluences. Surface textures, supporting higher and lower water wetting angles, were produced at the increasing above-threshold fluence, visualized by optical microscopy, and characterized regarding their water wetting. The different surface relief textures produced exhibit a drastic fluence-dependent drop (≈60°) of water contact angles until the superhydrophilic ones are produced, enabling the design and fabrication of surface microfluidic devices for chemical and biomedical applications.

Topography-dependent tuning of water wettability was achieved on a stainless steel surface textured by nanosecond-laser pulses at different laser fluences, with the minimal contribution of the surface chemical modification. Such differently-wet neighboring surface spots were demonstrated to drive an autonomous directional water flow. A series of elementary microfluidic devices based on the spatial wetting gradients were designed and tested as building blocks of “green”, energy-saving autonomous microfluidic circuits.

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