Abstract
A range of different superwettabilities were obtained on femtosecond laser-structured Al surfaces. The formation mechanism of each superwetting state is discussed in this paper. It is revealed that the underwater oil droplet and bubble wettabilities of a solid surface have a close relationship with its water wettability. The laser-induced hierarchical microstructures showed superhydrophilicity in air but showed superoleophobicity/superaerophobicity after immersion in water. When such microstructures were further modified with a low-surface-energy monolayer, the wettability of the resultant surface would turn to superhydrophobicity with ultralow water adhesion in air and superoleophilicity/superaerophilicity in water. The understanding of the relationship among the above-mentioned six different superwettabilities is highly important in the design of various superwetting microstructures, transforming the structures from one superwetting state to another state and better using the artificial superwetting materials.
Highlights
There are three common states of matter in our daily life, i.e., solid, liquid, and gas
The great water repellency and the self-cleaning function of the lotus leaf are caused by the collective effects of the binary microstructures and the hydrophobic wax-crystal coating on its surface.[20−22] In addition, fish skin resists oil contamination because the fish scales show underwater superoleophobicity that endow fish scales with great anti-oil ability in water.[23]
We find that the laser-induced rough surface has excellent superhydrophilicity, underwater superoleophobicity, and underwater superaerophobicity for more than one month as long as the sample is stored in water, while the laserinduced F-rough surface is able to always preserve superhydrophobicity, underwater superoleophilicity, and underwater superaerophilicity even the sample is stored in air
Summary
There are three common states of matter in our daily life, i.e., solid, liquid, and gas. A hierarchical microstructured pattern was created on an Al surface via femtosecond (fs) laser pulses. The original laser-structured surface was superhydrophilic in air and had superoleophobicity/aerophobicity in water. Six kinds of different superwetting states were obtained on the laser-induced microstructures. The irradiated materials on the Al surface are heavily removed away, so microgrooves are generated in the center of the laser scanning lines. The material near the spot center is removed and sputtered above the Al substrate in the form of nanoscale molten particles. The wettabilities of the water droplet and the underwater oil droplet/ bubble on the as-prepared surfaces were investigated by a SL2000KB directly obtained by a one-step femtosecond laser treatment. The dynamic processes related to wettability were captured by a camera at 25 frames per second
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