Materials Science

Try to bend an icicle and it’ll snap in two. With its tendency to crack into shards, ice’s reputation for being stiff and brittle seems well-established. But thin, pristine threads of ice are bendy and elastic, scientists report in the July 9 Science.

To create the flexible ice, Peizhen Xu of Zhejiang University in Hangzhou, China and colleagues used a needle with an electric voltage applied to it, which attracted water vapor within a chilled chamber. The resulting ice whiskers were a few micrometers in diameter or less, a fraction of the width of a typical human hair.

Usually, ice contains defects: tiny cracks, pores or misaligned sections of crystal. But the specially grown ice threads consisted of near-perfect ice crystals with atypical properties. When manipulated at temperatures of –70° Celsius and –150° C, the ice could be curved into a partial circle with a radius of tens of micrometers. When the bending force was released, the fibers sprang back to their original shape.

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Researchers bent a tiny fiber of ice (thin white line) into a loop, showing that the usually brittle material can be flexible under certain conditions.

Bending the fibers compresses the ice on its inside edge. The new measurements indicate that the compression induces the ice to take on a different structure. That’s to be expected for ice, which is known to morph into a variety of phases depending on pressure and temperature (SN: 1/11/09). The discovery could give researchers a new way to study ice’s properties when squeezed.

Thin ice strands form naturally in snowflakes. Unlike the ice in the experiment, snowflakes don’t consist of single, flawless ice crystals. But small sections of the flakes could be single crystals, the researchers say, suggesting that tiny bits of snowflakes could also bend. More

This pasta is no limp noodle.

When imprinted with carefully designed arrangements of grooves, flat pasta morphs as it cooks, forming tubes, spirals and other shapes traditional for the starchy sustenance. The technique could allow for pasta that takes up less space, Lining Yao and colleagues report May 5 in Science Advances.

Pasta aficionados “are very picky about the shapes of pasta and how they pair with different sauces,” says Yao, who studies the design of smart materials at Carnegie Mellon University in Pittsburgh. But those shapes come at a cost of excess packaging and inefficient shipping: For some varieties of curly pasta, more than 60 percent of the packaging space is used to hold air, the researchers calculated.

Yao and colleagues stamped a series of grooves onto one side of each noodle. As the pasta absorbed water during cooking, the liquid couldn’t penetrate as fully on the grooved side, causing it to swell less than the smooth side of the pasta. That asymmetric swelling bent the previously flat noodle into a curve. By changing the arrangement of the grooves, the researchers controlled the final shape. Computer simulations of swelling pasta replicated the shapes seen in the experiments.

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Flat pasta (top) with the right pattern of grooves imprinted on it curls into traditional pasta shapes when boiled. Computer simulations of the pasta (bottom) show the same behavior.

The technique isn’t limited to pasta: Another series of experiments, performed with silicone rubber in a solvent, produced similar results. But whereas the pasta held its curved shape, the silicone rubber eventually absorbed enough solvent to flatten out again. The gluey nature of cooked pasta helps lock in the twists by fusing neighboring grooves together, the researchers determined. Removing the silicone from the solvent caused the silicone to bend in the opposite direction. This reversible bending process could be harnessed for other purposes, such as a grabber for robot hands, Yao says.

The pasta makes particularly good camping food, Yao says. A member of her team brought it along on a recent hiking trip. The pasta slips easily into a cramped pack but cooks into a satisfying shape. More

Studying fabrics at very high magnification helps determine how some face masks filter out particles better than others. And the close-ups reveal an unseen beauty of the mundane objects that have now become an essential part of life around the world.

As scientists continue to show how effective masks can be at slowing the spread of the new coronavirus, particularly when they have a good fit and are worn correctly, some have taken microscopic approaches (SN: 2/12/21).

“Embedded in microscale textures are clues as to why materials have various properties,” says Edward Vicenzi, a microanalysis expert at the Smithsonian’s Museum Conservation Institute in Suitland, Md. “Unraveling that evidence turns out to be a fun job.”

Before the pandemic, Vicenzi spent his days observing meteorites, stones and other museum specimens under the microscope. But in March 2020, as the COVID-19 pandemic progressed, he and colleagues from the National Institute for Standards and Technology in Gaithersburg, Md., felt a strong desire to contribute to beating back the virus. So they started studying face-covering materials instead.

Cotton flannel: A network of cotton fibers “hovers” above a woven surface in this view of the fabric. This chaotic arrangement gives cotton flannel fibers additional opportunities to grab particles as they flow through the fabric. E.P. Vicenzi/Smithsonian’s Museum Conservation Institute and NIST

Polyester-cotton blend: Disheveled natural cotton fibers (pale) contrast with nearly identical polyester fibers (blue) in this false-color image. Polyester fibers are highly organized, mostly straight and smooth, making them less effective than cotton fibers alone at trapping nanoscale particles. E.P. Vicenzi/Smithsonian’s Museum Conservation Institute and NIST

Rayon: Like patterns observed on rigatoni pasta, grooves run along the length of rayon fibers. Unlike cotton flannels, rayon has no apparent weblike structures formed from raised fibers, making it easier for particles to move from one side of the synthetic fabric to the other. E.P. Vicenzi/Smithsonian’s Museum Conservation Institute and NIST

Wool flannel: Seen in cross-section, these fibers resemble a hurricane swirl. Wool flannel can also form fiber webs that block particles, but those webs are not as effective as ones in 100-percent cotton, researchers found. E.P. Vicenzi/Smithsonian’s Museum Conservation Institute and NIST

N95 mask: In an N95 mask (seen in false color cross-section), a thin outer layer (top) and thick inner layer (bottom) sandwich a filtration layer (purple), which traps the smallest particles. The multilayered assemblage made of plastic is melted and blown into a weblike fabric, which makes N95s filter particles better than cloth masks, even cotton ones. E.P. Vicenzi/Smithsonian’s Museum Conservation Institute and NIST

Using a scanning electron microscope, Vicenzi and colleagues have examined dozens of materials, including coffee filters, pillowcases, surgical masks and N95 masks. In 2020, the team found that N95 respirator masks are the most effective at providing protection from aerosols like the ones in which SARS-CoV-2, the virus that causes COVID-19, travels. And the researchers reported that synthetic fabrics, like chiffon or rayon, don’t trap as many particles as tightly woven cotton flannels.

Microscopic textures can explain each fabric’s ability to filter out aerosols. The random nature of cotton fibers — with its wrinkled texture and complex shapes such as kinks, bends and folds — probably allows cotton to trap more nanoscale particles than other fabrics, Vicenzi says. In contrast, polyester fabrics have highly organized, mostly straight and smooth fibers, which makes them less efficient as face masks.

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Cotton flannels also provide additional protection by absorbing moisture from breath, Vicenzi and colleagues report March 8 in ACS Applied Nano Materials.

“Since cotton loves water, it swells up in humid environments, and that makes it harder for particles to make their way through a mask,” says Vicenzi. Polyester and nylon masks, on the other hand, “repel water from your breath, so there’s no added benefit.”

Through his work, Vicenzi has explored the unseen world of face-covering materials. Some textiles remind him of food, such as rayon’s fibers that resemble the texture of rigatoni pasta. Others, like wool, remind him of atmospheric patterns such as the swirl of a hurricane.

Vicenzi plans to keep observing face masks up close. And he hopes his research helps people decide how to best protect themselves and others during the COVID-19 pandemic. “It’s nice to use an effective material for a mask if you can,” he says. “However, wearing any mask compared to none at all makes the biggest difference in slowing the spread of pathogens.”

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Inspired by a strange fish that can withstand the punishing pressures of the deepest reaches of the ocean, scientists have devised a soft autonomous robot capable of keeping its fins flapping — even in the deepest part of the Mariana Trench.
The team, led by roboticist Guorui Li of Zhejiang University in Hangzhou, China, successfully field-tested the robot’s ability to swim at depths ranging from 70 meters to nearly 11,000 meters, it reports March 4 in Nature.
Challenger Deep is the lowest of the low, the deepest part of the Mariana Trench. It bottoms out at about 10,900 meters below sea level (SN: 12/11/12). The pressure from all that overlying water is about a thousand times the atmospheric pressure at sea level, translating to about 103 million pascals (or 15,000 pounds per square inch). “It’s about the equivalent of an elephant standing on top of your thumb,” says deep-sea physiologist and ecologist Mackenzie Gerringer of State University of New York at Geneseo, who was not involved in the new study.

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The tremendous pressures at these hadal depths — the deepest ocean zone, between 6,000 and 11,000 meters — present a tough engineering challenge, Gerringer says. Traditional deep-sea robots or manned submersibles are heavily reinforced with rigid metal frames so as not to crumple — but these vessels are bulky and cumbersome, and the risk of structural failure remains high.
To design robots that can maneuver gracefully through shallower waters, scientists have previously looked to soft-bodied ocean creatures, such as the octopus, for inspiration (SN: 9/17/14). As it happens, such a deep-sea muse also exists: Pseudoliparis swirei, or the Mariana hadal snailfish, a mostly squishy, translucent fish that lives as much as 8,000 meters deep in the Mariana Trench.
In 2018, researchers described three newly discovered species of deep-sea snailfish (one shown) found in the Pacific Ocean’s Atacama Trench, living at depths down to about 7,500 meters. Also found in the Mariana Trench, such fish are well adapted for living in high-pressure, deep-sea environments, with only partially hardened skulls and soft, streamlined, energy-efficient bodies.Newcastle University
Gerringer, one of the researchers who first described the deep-sea snailfish in 2014, constructed a 3-D printed soft robot version of it several years later to better understand how it swims. Her robot contained a synthesized version of the watery goo inside the fish’s body that most likely adds buoyancy and helps it swim more efficiently (SN: 1/3/18).
But devising a robot that can swim under extreme pressure to investigate the deep-sea environment is another matter. Autonomous exploration robots require electronics not only to power their movement, but also to perform various tasks, whether testing water chemistry, lighting up and filming the denizens of deep ocean trenches, or collecting samples to bring back to the surface. Under the squeeze of water pressure, these electronics can grind against one another.
So Li and his colleagues decided to borrow one of the snailfish’s adaptations to high-pressure life: Its skull is not completely fused together with hardened bone. That extra bit of malleability allows the pressure on the skull to equalize. In a similar vein, the scientists decided to distribute the electronics — the “brain” — of their robot fish farther apart than they normally would, and then encase them in soft silicone to keep them from touching.
The design of the new soft robot (left) was inspired by the deep-sea snailfish (illustrated, right), which is adapted to live in the very high-pressure environments of the deepest parts of the ocean. The snailfish’s skull is incompletely ossified, or hardened, which allows external and internal pressures to equalize. Spreading apart the robot’s sensitive electronics and encasing them in silicone keeps the parts from squeezing together. The robots flapping fins are inspired by the thin pectoral fins of the fish (although the real fish doesn’t use its fins to swim).Li et al/ Nature 2021
The team also designed a soft body that slightly resembles the snailfish, with two fins that the robot can use to propel itself through the water. (Gerringer notes that the actual snailfish doesn’t flap its fins, but wriggles its body like a tadpole.) To flap the fins, the robot is equipped with batteries that power artificial muscles: electrodes sandwiched between two membranes that deform in response to the electrical charge.
The team tested the robot in several environments: 70 meters deep in a lake; about 3,200 meters deep in the South China Sea; and finally, at the very bottom of the ocean. The robot was allowed to swim freely in the first two trials. For the Challenger Deep trial, however, the researchers kept a tight grip, using the extendable arm of a deep-sea lander to hold the robot while it flapped its fins.
This machine “pushes the boundaries of what can be achieved” with biologically inspired soft robots, write robotocists Cecilia Laschi of the National University of Singapore and Marcello Calisti of the University of Lincoln in England. The pair have a commentary on the research in the same issue of Nature. That said, the machine is still a long way from deployment, they note. It swims more slowly than other underwater robots, and doesn’t yet have the power to withstand powerful underwater currents. But it “lays the foundations” for future such robots to help answer lingering questions about these mysterious reaches of the ocean, they write.
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Researchers successfully ran a soft autonomous robot through several field tests at different depths in the ocean. At 3,224 meters deep in the South China Sea, the tests demonstrated that the robot could swim autonomously (free swim test). The team also tested the robot’s ability to move under even the most extreme pressures in the ocean. A deep-sea lander’s extendable arm held the robot as it flapped its wings at a depth of 10,900 meters in the Challenger Deep, the lowest part of the Mariana Trench (extreme pressure test). These tests suggest that such robots may, in future, be able to aid in autonomous exploration of the deepest parts of the ocean, the researchers say.
Deep-sea trenches are known to be teeming with microbial life, which happily feed on the bonanza of organic material — from algae to animal carcasses — that finds its way to the bottom of the sea. That microbial activity hints that the trenches may play a significant role in Earth’s carbon cycle, which is in turned linked to the planet’s regulation of its climate.
The discovery of microplastics in Challenger Deep is also incontrovertible evidence that even the bottom of the ocean isn’t really that far away, Gerringer says (SN: 11/20/20). “We’re impacting these deep-water systems before we’ve even found out what’s down there. We have a responsibility to help connect these seemingly otherworldly systems, which are really part of our planet.” More

Containers that the U.S. government plans to use to store dangerous nuclear waste underground may be more vulnerable to water damage than previously thought. Millions of liters of highly radioactive waste from the U.S. nuclear weapons program are currently held in temporary storage units across the country. The government’s game plan for permanently disposing of […] More

Hotter objects typically glow brighter than cooler ones, making them stand out in infrared images. But a newly designed coating bucks the rule that hotter equals brighter. For certain wavelengths of infrared light, the material’s brightness doesn’t change as it warms, researchers report December 17 in Proceedings of the National Academy of Sciences. Made of […] More

Lead performs under pressure. Under normal conditions, the metal is relatively soft, easily scratched with a fingernail. But when compressed under extreme pressures, lead becomes hard and strong — even stronger than steel, scientists report November 11 in Physical Review Letters. To study how lead’s strength changed under pressure, researchers rapidly compressed a lead sample […] More

A new way to chill out is simple: Just unwind. Called twistocaloric cooling, the method involves unwinding tightly twisted strands of various materials. The technique was used to chill water by several degrees Celsius, scientists report in the Oct. 11 Science. Cooling techniques like those used in traditional refrigerators rely on cycles of compressing and […] More