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Fabrication of Superhydrophobic Stainless Steel Nozzles by Femtosecond Laser Micro-/Nano-Texturing

A dispensing nozzle is an essential mechanical element in inkjet, dot, and bioprinting. To improve the printing resolution, the inner diameter of the nozzle outlet must be as small as possible. A droplet dispensed through a hydrophilic stainless steel outlet expands on the whole outlet surface and along the side surface of the nozzle. This issue can be solved by physical surface modifications. In the present paper, a femtosecond laser micro-/nano-texturing method was developed to transform the originally hydrophilic stainless steel surface of a nozzle to a hydrophobic or superhydrophobic one. First, an AISI304 plate was used to demonstrate experimentally that, on its surface, the tailored micro-/nano-patterns were reproduced as micro-/nano-textures, making the surface superhydrophobic. Second, the technique was applied to the physical surface modification of an AISI304 stainless steel nozzle outlet by optimizing the femtosecond laser machining conditions. A high-speed camera was used to take a snapshot of the dispensed droplet from the surface-modified outlet. Finally, a line-printing experiment was performed to characterize the dispensing behavior of the stainless steel nozzles with and without physical surface modification.