The 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. Underwater gas can flow through this channel. When a microchannel connects two underwater bubbles, the gas spontaneously transports from the small bubble to the large bubble along this hollow microchannel. Gas self-transportation can be extended to more functions related to manipulating bubbles underwater, such as unidirectional gas passage and water/gas separation. Credit: Jiale Yong et al
The manipulation and use of gas in water have broad 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 via unique gradient geometries has been successfully archived, opening room for more research on this exciting topic. In many cases, however, the gradient geometry is microscope and unsuitable for transporting gas at microscope level because most microscale gradient structures provide the insufficient driving force. This makes underwater self-transportation of bubbles and gases at the microscopic level a big challenge.
In a new paper published in the International Journal of Extreme Manufacturing, a team of researchers, led by Prof. Feng Chen from the School of Electronic Science and Engineering, Xi’an Jiaotong University, China, have proposed an innovative strategy for underwater self-transportation of gas along a femtosecond laser-induced open superhydrophobic surface with a microchannel width less than 100 µm. The microgroove with superhydrophobic and underwater superaerophilic micro/ nanostructures on its inner wall cannot be wetted by water, so a hollow microchannel forms between the substrate and water as the groove-structured surface is immersed in water. Gas can freely flow along the underwater microchannel; that is, this microchannel enables gas transport in water. The superhydrophobic microgrooves make it possible to self-transport bubbles and gases at the microscopic level.
Femtosecond (10−15 s) laser technology has emerged as a promising solution to prepare such a superhydrophobic microgroove. Leveraging on its two key features: 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 material’s surface. Thus, the femtosecond laser is a viable tool for creating superhydrophobic microstructures on material surfaces, which is essential for realizing gas self-transportation at 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 superhydrophobicity and underwater superaerophilicity. The femtosecond laser-induced superhydrophobic and underwater superaerophilic microgrooves greatly repel water and can support gas transportation underwater because a hollow microchannel formed between the PTFE surface and water medium in water. Underwater gas was easily transported through this hollow microchannel.
Interestingly, when superhydrophobic microgrooves connect different superhydrophobic regions in water, the gas spontaneously transfers from a small region to a large region. A unique laser drilling process can also integrate the microholes into the superhydrophobic and underwater superaerophilic PTFE sheet.
The asymmetric morphology of the femtosecond laser-induced ‘Y’-shaped microholes and the unique surface superwettability of the PTFE sheet allowed the gas bubbles to unidirectionally pass through the porous superwetting PTFE sheet (from the small-holes side to the big-holes side) in the water.
Anti-buoyancy unidirectional penetration was achieved; that is, the gas overcame the buoyance of the bubble and self-transported downward. Similar to a diode, the function of the unidirectional gas passage of the superwetting porous sheet was used to determine the gas’s transporting direction in manipulating underwater gas, preventing gas backflow.
The Laplace pressure difference drove the processes of spontaneous gas transportation and unidirectional bubble passage. The superhydrophobic and underwater superaerophilic porous sheets were also successfully used to separate water and gas based on the behavior of gas self-transportation.
Professor Feng Chen (Director of Ultrafast Photonic Laboratory, UPL) and Associate Professor Jiale Yong have identified the significance of the research and the potential applications of this technology (underwater gas self-transportation) as follows:
“How to think of using superhydrophobic microgrooves for gas transportation?”
“Superhydrophobic microstructures have great water repellence, allowing the 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 forms between the substrate and water medium. This microchannel enables gas transport in water so that gas can freely flow along the underwater microchannel. The femtosecond laser can easily fabricate such a superhydrophobic microgroove. The width of the laser-induced microgroove determines the width of the hollow microchannel, which is less than 100 μm, enabling us to realize gas self-transportation at microscopic level.”
“Why was femtosecond laser used to prepare such a superhydrophobic microgroove for gas self-transportation?”
“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 that can directly write superhydrophobic and underwater superaerophilic microgrooves on the surface of a solid substrate and drill open microholes through a thin film. Furthermore, the track of the open microgrooves and the location of the open microholes can be accurately designed by the control program during laser processing.”
“Does the types of the gas affect the self-transportation of bubbles and gases at microscopic level?”
“Although just the ordinary air bubble has been studied, it should be noticed that the driving force for gas transportation does not involve the chemical composition of the gas. Therefore, the manipulation of gas reported in this paper is applicable to other gases as long as they do not completely dissolve into the corresponding liquids.”
“What are the potential applications of the technology achieving bubble/gas self-transportation and manipulation based on the femtosecond laser-written superhydrophobic microgrooves?”
“We believe the reported methods of self-transporting gas in water along femtosecondlaser-structured superhydrophobic microchannels will open up many new applications in energy utilization, chemical manufacturing, environmental protection, agricultural breeding, microfluidic chips, health care, etc.”
Researchers also point out that this strategy for self-transporting gas based on the superhydrophobic microgrooves, while validated, is still in its infancy. The influence of various factors (such as the size of the microgrooves, the length of the channel, and the volume of the gas) on the performance of gas transportation needs further research. The practical applications based on the gas self-transportation function also need to be developed.
More information:
Jiale Yong et al, Underwater gas self-transportation along femtosecond laser-written open superhydrophobic surface microchannels (100 µm) for bubble/gas manipulation, International Journal of Extreme Manufacturing (2021). DOI: 10.1088/2631-7990/ac466f
Provided by
International Journal of Extreme Manufacturing
Citation:
Femtosecond laser bionic fabrication enabling bubble manipulation (2022, July 27)
retrieved 28 July 2022
from https://phys.org/news/2022-07-femtosecond-laser-bionic-fabrication-enabling.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
