Reducing Adhesion for Dispensing Tiny Water/Oil Droplets and Gas Bubbles by Femtosecond Laser-Treated Needle Nozzles: Superhydrophobicity, Superoleophobicity, and Superaerophobicity

Three-level microstructures were formed on the stainless-steel surfaces by simple femtosecond laser ablation. The structured surfaces exhibit superhydrophilicity in air and superoleophobicity/superaerophobicity in water. After further stearic acid modification, the surfaces turned to superhydrophobicity and underwater superoleophilicity/superaerophilicity. Through this technique, the nozzle of a needle is transformed to possess superwettabilities. When the nozzles were used to release liquid and gas, the sizes of the dispensed water and oil droplets and air bubbles were dramatically reduced. Particularly, we demonstrate that the underwater superaerophobic nozzle could dispense air bubbles in nanoliter volume without the need of reducing the nozzle diameter. The liquid retention at the opening of the needle was also effectively prevented. Therefore, the reduced droplet/bubble size and retention allow us to achieve a dramatically enhanced volume accuracy and resolution during manipulation and transport of aqueous solutions and gases. The femtosecond laser-induced superwetting nozzles can be used in high-resolution liquid transport, inkjet printing, 3D printing, pipettes, medical devices, cell engineering, biological detection, microchemical reactor, and reducing industrial gas emission.