(Press-News.org) Imagine staying dry underwater for months. Now Northwestern University engineers have examined a wide variety of surfaces that can do just that -- and, better yet, they know why.
The research team is the first to identify the ideal "roughness" needed in the texture of a surface to keep it dry for a long period of time when submerged in water. The valleys in the surface roughness typically need to be less than one micron in width, the researchers found. That's really small -- less than one millionth of a meter -- but these nanoscopic valleys have macroscopic impact.
Understanding how the surfaces deflect water so well means the valuable feature could be reproduced in other materials on a mass scale, potentially saving billions of dollars in a variety of industries, from antifouling surfaces for shipping to pipe coatings resulting in lower drag. That's science and engineering, not serendipity, at work for the benefit of the economy.
"The trick is to use rough surfaces of the right chemistry and size to promote vapor formation, which we can use to our advantage," said Neelesh A. Patankar, a theoretical mechanical engineer who led the research.
"When the valleys are less than one micron wide, pockets of water vapor or gas accumulate in them by underwater evaporation or effervescence, just like a drop of water evaporates without having to boil it. These gas pockets deflect water, keeping the surface dry," he said.
In a study published today (Aug. 18) by the journal Scientific Reports, Patankar and his co-authors explain and demonstrate the nanoscale mechanics behind the phenomenon of staying dry underwater.
In their experiments, the researchers used a variety of materials with and without the key surface roughness and submerged them in water. Samples with the nanoscale roughness remained dry for up to four months, the duration of the experiment. Other samples were placed in harsh environments, where dissolved gas was removed from the ambient liquid, and they also remained dry.
"It was amazing and what we were hoping for," said Patankar, a professor of mechanical engineering in the McCormick School of Engineering and Applied Science. "My lab likes to defy normal experience. In this work, we looked for properties that manipulate the water phase changes we know."
The researchers also report that nature uses the same strategy of surface roughness in certain aquatic insects, such as water bugs and water striders. Small hairs on the surfaces of their body have the less-than-one-micron spacing, allowing gas to be retained between the hairs.
"These gas-retaining insects have surface properties consistent with our predictions, allowing them to stay dry for a long time," said Paul R. Jones, the study's first author. He is a Ph.D. student in Patankar's research group.
The researchers focused on the nanoscopic structure of surfaces, which, at the nanoscale, are somewhat akin to the texture of a carpet, with tiny spike-like elevations separated by valley-shaped pores in between.
When submerged, water tends to cling to the top of the spikes, while air and water vapor accrue in the pores between them. The combination of trapped air and water vapor within these cavities forms a gaseous layer that deters moisture from seeping into the surface below.
"When we looked at the rough surfaces under the microscope, we could see clearly the vacant gaps -- where the protective water vapor is," Patankar said.
Historically, scientists had not understood how to keep water vapor from succumbing to condensation within the pore, which can cause water to wet the surface. But the Northwestern team found the molecular key: They demonstrated that when the valleys are less than one micron in width, they can sustain the trapped air as well as vapor in their gasified states, strengthening the seal that thwarts wetness.
INFORMATION:
The study, titled "Sustaining Dry Surfaces Under Water," also includes authors from ETH Zürich, Switzerland; Arizona State University; University of Illinois at Chicago; Massachusetts Institute of Technology; and the University of Denmark.
Movie and images are available at https://northwestern.box.com/s/l7dzy4b4gcftz3ef35k3wg6wh2hzukrp.
Source contact: Neelesh Patankar at 847-491-3021 or n-patankar@northwestern.edu END
(SACRAMENTO, Calif.) -- In a discovery that is likely to rewrite immunology text books, researchers at UC Davis have found that early exposure to inflammatory cytokines, such as interleukin 2, can "paralyze" CD4 T cells, immune components that help orchestrate the body's response to pathogens and other invaders.
This mechanism may act as a firewall, shutting down the immune response before it gets out of hand. However, from a clinical standpoint, this discovery could lead to more effective cancer immunotherapies, better drugs for autoimmune conditions and new ways to ...
Scientists are planning for a future in which superbugs gain the upper hand against our current arsenal of antibiotics. One emerging class of drug candidates, called AMLPs (antimicrobial lipopeptides), shows promise, and an August 18 study in the Biophysical Journal explains why: they selectively kill bacterial cells, while sparing mammalian host cells, by clumping together into microscopic balls that stick to the bacterial membrane--a complex structure that will be slower to mutate and thus resist drugs.
"The pressing need for novel antibiotics against resistant strains ...
SAN FRANCISCO--Early data coming in from a massive, four-year deployment of seismometers onshore and offshore in the Pacific Northwest are giving scientists a clearer picture of the Cascadia subduction zone, a region with a past and potential future of devastating "megathrust" earthquakes.
The preliminary results from the Cascadia Initiative include a report of previously undetected, small earthquakes offshore, and seismic imaging that reveals new offshore structures at the subduction zone. The reports, published as a focus section in the September-October 2015 issue ...
Research indicates that the use of condoms may cause some men to experience erection difficulties. However, in a study of 479 heterosexual men who used condoms and were 18 to 24 years old, those who reported condom-associated erection problems were also more likely to experience more generalized erection difficulties.
Investigators also found that more than one-third of participants had never been taught how to use a condom correctly. Clinicians should assess whether men using condoms experience condom-associated erection problems and where appropriate, make referrals ...
Liver diseases affect hundreds of millions of people and cause significant illness and death. A new study indicates that liver scarring (or fibrosis), which can ultimately lead to liver failure, is fairly common. It was present in 5.6% of adults in the Rotterdam Study, a population-based study among individuals in a suburb of Rotterdam, the Netherlands, who were ?45 years old. It was especially prevalent in individuals with diabetes or steatosis, the latter of which occurs when fat cells infiltrate the liver.
"In the context of an aging population and an increasing prevalence ...
New research indicates that use of oral contraceptives may provide benefits for women with inflammatory arthritis.
Among 273 women with early inflammatory arthritis, women who had used oral contraceptives in the past and those who were currently using them reported fewer problems related to how well they can function, their mood, and how active their disease is.
The findings are published in Arthritis Care & Research.
INFORMATION: ...
It's known that brain changes are present in drug addicts even when they have been abstinent for a short period of time. Now new research shows that alterations persist in long-term abstinent heroin-depended individuals as well.
Through the use of functional magnetic resonance imaging, investigators analyzed the brains of 30 heroin-addicted individuals after a long period of abstinence (more than 3 years) and compared the results with those of 30 healthy controls.
The team found that in the former heroin users, there was significant dysfunctional activity in the nucleus ...
The fourth tropical depression of the Atlantic Ocean hurricane season formed today, August 18, 2015 as NASA's Terra satellite passed overhead.
On Aug. 18 at 8:45 a.m. EDT the Moderate Resolution Imaging Spectroradiometer or MODIS instrument aboard NASA's Terra satellite captured a visible image of newborn Tropical Depression 4 in the central Atlantic Ocean. The image showed thunderstorms banding around the center of circulation in all quadrants except the northwest.
The National Hurricane Center (NHC) also uses measurements from the Advanced Scatterometer or ASCAT instrument ...
NASA-NOAA's Suomi NPP satellite passed over Typhoon Goni and gathered infrared data that helped identify the strongest part of the storm as the south and eastern quadrants.
The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard NASA-NOAA's Suomi satellite captured an infrared image of Goni on August 18 at 4:18 UTC (12:18 a.m. EDT) that showed the strongest thunderstorms with the coldest cloud top temperatures (near -63F/-53C) were in the eastern and southern quadrants.
The Joint Typhoon Warning Center noted that animated enhanced infrared satellite ...
Irvine, Calif., Aug. 18, 2015 - Researchers from the University of California, Irvine and NASA have uncovered a remarkably strong link between high wildfire risk in the Amazon basin and the devastating hurricanes that ravage North Atlantic shorelines. The climate scientists' findings appear in the journal Geophysical Research Letters near the 10th anniversary of Hurricane Katrina's calamitous August 2005 landfall at New Orleans.
"Hurricane Katrina is indeed part of this story," said James Randerson, Chancellor's Professor of Earth system science at UCI and senior author ...
