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

Abstract

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.

A review of femtosecond laser-structured superhydrophobic or underwater superoleophobic porous surfaces/materials for efficient oil/water separation

“…70,107,111,112,[155][156][157][158][159][160][161][162][163][164][165] The outstanding features of fs laser microfabrication make this technology have great success in designing wettability of solid materials. [47][48][49][50][51][52][53][54][55]61,[73][74][75][76][77]152,[166][167][168][169][170][171] Compared to the common methods for achieving superhydrophobicity and underwater superoleophobicity, fs laser microfabrication has some particularly special aspects. Firstly, the fs laser is able to ablate most of the materials, without being restricted to specic materials.…”

Endowing Metal Surfaces With Underwater Superoleophobicity by Femtosecond Laser Processing for Oil-Water Separation Application

“…Interestingly, most kinds of metals are inherently hydrophilic. The femtosecond laser can ablate almost all of the known materials and then can create micro/nanoscale structures on the surface of various metals; [21][22][23][24][25] thereby underwater superoleophobicity can be easily achieved on different metals by femtosecond laser treatment, such as Ti, [37] stainless steel, [38] Al, [34] Cu, [39] Mo, and so on [32,40]. With the laser-induced underwater superoleophobic surface microstructures, a wide range of metallic sheets can potentially be endowed with the ability of oil-water separation.…”

Femtosecond-Laser-Produced Underwater “Superpolymphobic” Nanorippled Surfaces: Repelling Liquid Polymers in Water for Applications of Controlling Polymer Shape and Adhesion

“…Therefore, the underwater PDMS droplet sits on a composite (water/solid) interface and is at the underwater Cassie state (Figure 4d). 1,47−49 The PDMS droplet touches only a small area of the surface microstructures, and most area of the PDMS surface is surrounded by water. The hierarchical microstructure and the trapped water layer can effectively reduce the contact area, as well as van der Waals force, between the sample surface and the PDMS droplet, leading to a small adhesive force and adhesion of the laser-textured stainless steel surface to liquid polymer in water.…”

“…Typical line-by-line scanning was adopted to ablate sample surface (Figure 1b). 27,28,49,57,58 The laser power and scanning speed were set constantly at 500 mW and 2.5 mm s –1 , respectively. The interval (Λ) of the laser scanning lines was controlled by the program.…”