Femtosecond laser-induced hierarchical micro/nanostructures promote superhydrophobicity in air and excellent underwater superaerophilicity on the polytetrafluoroethylene (PTFE) surface. Immersing the PTFE surface with superhydrophobic microgrooves in water generates hollow microchannels between the PTFE substrate and the water medium. Subsea gas can flow through this channel. When a microchannel connects two underwater bubbles, gas spontaneously transports from the small bubble to the large bubble along this hollow microchannel. Gas self-transport can be extended to further functions related to underwater bubble handling, such as unidirectional gas passage and water/gas separation. Credit: Jiale Yong et al
The manipulation and use of gas in water has wide applications in energy utilization, chemical manufacturing, environmental protection, agricultural breeding, microfluidic chips, and health care. The possibility of driving underwater bubbles to move directionally and continuously over a given distance using unique gradient geometries has been successfully filed, opening the door for further research on this exciting topic. In many cases, however, the gradient geometry is microscopic and not suitable for transporting gas at the microscopic level because most microscale gradient structures provide insufficient driving force. This makes the underwater self-transport of bubbles and gases at the microscopic level a major challenge.
In a new article published in the International magazine of extreme manufacturing, a team of researchers, led by Professor Feng Chen from the School of Electronic Science and Engineering, Xi’an Jiaotong University, China, has proposed an innovative strategy for underwater gas self-transport along a surface femtosecond laser-induced open superhydrophobicity. with a microchannel width of less than 100 µm. The microgroove with underwater superhydrophobic and superaerophilic micro/nanostructures on its inner wall cannot be wetted by water, so a hollow microchannel is formed between the substrate and water as the groove-structured surface is immersed in Water. The gas can flow freely along the underwater microchannel; that is to say, this microchannel allows the transport of gas in the water. The superhydrophobic microgrooves allow self-transport of bubbles and gases at the microscopic level.
Femtosecond (10−15 s) laser technology has emerged as a promising solution to prepare a superhydrophobic microgroove. Taking advantage of their two key characteristics: extremely high peak intensity and ultrashort pulse width, femtosecond lasers have become an essential tool for modern extreme and ultra-precision manufacturing. Femtosecond laser processing has the characteristics of high spatial resolution, small heat-affected zone, and non-contact manufacturing. In particular, the femtosecond laser can ablate almost any material, resulting in microstructures on the surface of the material. Thus, the femtosecond laser is a viable tool to create superhydrophobic microstructures on material surfaces, which is essential to realize gas self-transport at the microscopic level.
Hierarchical micro/nanostructures were easily produced on the inherently hydrophobic polytetrafluoroethylene (PTFE) substrate by femtosecond laser processing, endowing the PTFE surface with excellent underwater superhydrophobicity and superaerophilicity. The femtosecond laser-induced underwater superhydrophobic and superaerophilic microgrooves are highly water-repellent and can support underwater gas transport because a hollow microchannel was formed between the PTFE surface and the water medium in the water Subsea gas was easily transported through this hollow microchannel.
Interestingly, when superhydrophobic microgrooves connect different superhydrophobic regions in water, gas is spontaneously transferred from a small region to a large region. A unique laser drilling process can also integrate the microholes into the underwater superhydrophobic and superaerophilic PTFE sheet.
The asymmetric morphology of the femtosecond laser-induced “Y” microholes and the unique surface superwettability of the PTFE sheet allowed gas bubbles to pass unidirectionally through the porous superwetting PTFE sheet (from the side of the holes small to next to large holes). ) to the water.
One-way anti-buoyancy penetration was achieved; that is, the gas overcame the buoyancy of the bubble and self-transported downward. Similar to a diode, the one-way gas pass function of the superwetting porous sheet was used to determine the direction of gas transport in subsea gas handling, preventing gas backflow.
The Laplace pressure difference drove the processes of spontaneous gas transport and unidirectional bubble passage. Underwater superhydrophobic and superaerophilic porous sheets were also successfully used to separate water and gas based on gas self-transport behavior.
Professor Feng Chen (Director of the Ultrafast Photonics Laboratory, UPL) and Associate Professor Jiale Yong have identified the research importance and potential applications of this technology (undersea gas self-transport) as follows:
“How to think about using superhydrophobic microgrooves for gas transport?”
“Superhydrophobic microstructures have high water repellency, allowing materials to repel liquids. If a microgroove has superhydrophobic micro/nanostructures on its inner wall, the microgroove will not be wetted by water, as the groove-structured surface is immersed in water. Therefore, a hollow microchannel is formed between the substrate and the water medium. This microchannel allows the transport of gas into the water so that the gas can flow freely along of the underwater microchannel. The femtosecond laser can easily fabricate a superhydrophobic microgroove. The width of the laser-induced microgroove determines the width of the hollow microchannel, which is less than 100 μm, which allows us to realize gas self-transport at the microscopic”.
“Why was femtosecond laser used to prepare such a superhydrophobic microgroove for gas self-transport?”
“The laser is one of the greatest inventions of the 20th century. In recent years, the femtosecond laser has become an essential tool for modern extreme and ultra-precision manufacturing. Femtosecond laser processing is a flexible technology which can directly write underwater superhydrophobic and superaerophilic microgrooves on the surface of a solid substrate and drill open microholes through a thin film.In addition, the control program can precisely design the track of the open microgrooves and the location of microholes opened during laser processing”.
“Do gas types affect the self-transport of bubbles and gases at the microscopic level?”
“Although only the normal air bubble has been studied, it should be noted that the driving force for gas transport does not involve the chemical composition of the gas. Therefore, the gas manipulation described in this paper it is applicable to other gases as long as they do not dissolve completely in the corresponding liquids”.
“What are the potential applications of the technology to achieve bubble/gas self-transport and manipulation based on femtosecond laser-written superhydrophobic microgrooves?”
“We believe that the reported methods of gas self-transport in water along femtosecond laser-structured superhydrophobic microchannels will open many new applications in energy utilization, chemical manufacturing, environmental protection, agricultural breeding, microfluidic chips, medical of health, etc.”
The researchers also point out that this strategy of gas self-transport based on the superhydrophobic microgrooves, although validated, is still in its infancy. The influence of various factors (such as microgroove size, channel length, and gas volume) on gas transport performance needs further investigation. It is also necessary to develop the practical applications based on the self-transport function of gas.
New technology can help repel water and save lives through improved medical devices. More information: Jiale Yong et al, Underwater gas self-transportation along femtosecond laser-written open superhydrophobic surface microchannels (International Journal of Extreme Manufacturing (2021). DOI: 10.1088/2631). -7990/ac466f
Provided by International Journal of Extreme Manufacturing
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