The work aims to propose a new method to achieve controlled discontinuous dewetting by preparing patterned superhydrophobic surfaces through laser etching. Superhydrophobic surfaces were prepared by combining laser etching with Fluorinated Alkyl Silane (FAS) modification, and then superhydrophilic patterns were constructed via secondary laser etching to realize surface patterning. The effects of key laser parameters, such as power, scanning speed, scanning spacing, frequency, and processing times, on surface wettability were investigated systematically, and the surface microstructure and chemical composition were characterized through Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). In addition, the mechanical stability, chemical stability, thermal stability, and self-cleaning performance of the prepared aluminum-based superhydrophobic surface were evaluated, and the discontinuous dewetting behavior of the notched ring superhydrophilic pattern was studied in detail. The aluminum sheet surface achieved the optimal superhydrophobic performance under the following parameters: laser power P=9 W, scanning speed v=1 000 mm/s, scanning spacing x=10 μm, processing times t=2, and frequency f=30 Hz, at a contact angle of 161°±1° and a sliding angle of 1.7°±0.5°. SEM observations revealed that these parameters induced the formation of a micro-nano hierarchical structure similar to that of a lotus leaf surface, which trapped air, thereby enhancing hydrophobicity. EDS analysis confirmed the successful modification of FAS and the effective removal of the FAS layer after secondary etching, verifying the controllable regulation of wettability. The Al-based superhydrophobic surface exhibited excellent stability and could withstand 10 wear cycles, 20 adhesion-peeling cycles, and 10 thermal cycles without losing superhydrophobicity. In terms of chemical stability, it could maintain superhydrophobicity for 6 hours in 1 mol/L HCl solution, 3 hours in 1 mol/L NaOH solution, and more than 12 hours in 3.5% NaCl solution. Self- cleaning tests showed that rolling water droplets effectively removed fine sand, hydrophilic SiO2 particles, and hydrophobic SiO2 particles on a 30° inclined surface. This method was universal for various metals. The surfaces of Fe, Zn, brass, Pb, Ti, 304 stainless steel, Cu and Mg were originally hydrophilic, but after treatment, their contact angles exceeded 150° and sliding angles were less than 10°, achieving superhydrophobicity. Moreover, patterning was realized through secondary etching. The focus of this study was the discontinuous dewetting behavior of the notched ring superhydrophilic pattern. The effects of the tilt angle θ of the patterned surface, the ring diameter Φ, the notch angle α, and the dewetting direction on droplet capture were explored. The results showed that the droplet volume decreased with the increase of the tilt angle θ. Under different parameters, the droplet states were divided into three types: liquid film, droplet-like, and continuous dewetting. In conclusion, the laser etching method can simply and efficiently prepare patterned superhydrophobic surfaces with excellent mechanical, chemical, and thermal stability, as well as good self-cleaning performance. The controllable discontinuous dewetting characteristic of the notched ring pattern makes it have broad application prospects in the fields of microfluidics, high-throughput screening, and quantitative analysis.
Key words
laser etching /
superhydrophobic /
patterned surface /
stability /
water droplet /
discontinuous dewetting
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Funding
National Natural Science Foundation of China (U23A20632, 52275420)
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