Tag Archives: material

New ‘super jelly’ is soft, but strong enough to withstand the weight of a few cars

It’s not easy being soft and strong at the same time — unless you’re the new hydrogel developed at the University of Cambridge. This is the first soft material that has such a huge degree of resistance to compression, the authors report.

Image credits Zehuan Huang.

A new material developed by researchers at the University of Cambridge looks like a squishy gel normally, but like an ultra-hard, shatterproof glass when compressed — despite being 80% water. Its secret lies in the non-water portion of the material; this consists of a polymer network with elements held together by “reversible interactions”. As these interactions turn on and off, the properties of the materials shift.

The so-dubbed ‘super jelly’ could be employed for a wide range of applications where both strength and softness are needed such as bioelectronics, cartilage replacement in medicine, or in flexible robots.

Hardy hydrogel

“In order to make materials with the mechanical properties we want, we use crosslinkers, where two molecules are joined through a chemical bond,” said Dr. Zehuan Huang from the Yusuf Hamied Department of Chemistry, the study’s first author.

“We use reversible crosslinkers to make soft and stretchy hydrogels, but making a hard and compressible hydrogel is difficult and designing a material with these properties is completely counterintuitive.”

The macroscopic properties of any substance arise from its microscopic properties — its molecular structure and the way its molecules interact. Because of the way hydrogels are structured, it’s exceedingly rare to see such a substance show both flexibility and strength.

The team’s secret lay in the use of molecules known as cucurbiturils. These are barrel-shaped molecules that the team used as ‘handcuffs’ to hold other polymers together (a practice known as ‘crosslinking’). This holds two ‘guest molecules’ inside the cavity it forms, which were designed to preferentially reside inside the cucurbituril molecule. Because the polymers are linked so tightly, the overall material has a very high resistance to compression (there isn’t much free space at the molecular level for compression to take place).

The alterations the team made to the guest molecules also slows down the internal dynamics of the material considerably, they report. This gives the hydrogel overall properties ranging between rubber-like and glass-like states. According to their experiments, the gel can withstand pressures of up to 100 MPa (14,503 pounds per square inch). An average car, for comparison, weighs 2,871 pounds.

“The way the hydrogel can withstand compression was surprising, it wasn’t like anything we’ve seen in hydrogels,” said co-author Dr. Jade McCune, also from the Department of Chemistry. “We also found that the compressive strength could be easily controlled through simply changing the chemical structure of the guest molecule inside the handcuff.”

“People have spent years making rubber-like hydrogels, but that’s just half of the picture,” said Scherman. “We’ve revisited traditional polymer physics and created a new class of materials that span the whole range of material properties from rubber-like to glass-like, completing the full picture.”

The authors say that, as far as they know, this is the first time a glass-like hydrogel has been developed. They tested the material by using it to build a real-time pressure sensor to monitor human motions.

They’re now working on further developing their glass-like hydrogel for various biomedical and bioelectronic applications.

The paper “Highly compressible glass-like supramolecular polymer networks” has been published in the journal Nature Materials.

Batman cloak-like chainmail switches from flexible to tough on command

Credit:Caltech.

Researchers at Caltech and JPL have devised a new smart material that can instantly morph from fluid and flexible to tough and rigid. The material’s configuration is inspired by chainmail armors and could potentially prove useful in exoskeletons, casts for broken limbs, and robotics.

This modern chainmail sounds mighty similar to Batman’s cloak, which drapes behind the superhero at rest but stiffens into a glider when he needs to make a fast escape. However, unlike the DC movies, the technology was initially inspired by the physics of vacuum-packed coffee.

Coffee inspiration

 “Think about coffee in a vacuum-sealed bag. When still packed, it is solid, via a process we call ‘jamming’. But as soon as you open the package, the coffee grounds are no longer jammed against each other and you can pour them as though they were a fluid,” Chiara Daraio, a professor of mechanical engineering and applied physics at Caltech, explained.

While individual coffee grounds or sand particles only jam when compressed, sheets of linked rings can jam together under both compression and tension. Starting from this idea, Daraio and colleagues experimented with a number of different configurations of linked particles and tested each using both computer simulations and 3-D printing.

Testing the impact resistance of the material when unjammed (soft). Credit: Caltech.
Testing the impact resistance of the material when jammed (rigid). Credit: Caltech.

Although it doesn’t lead to the stiffest configuration, the researchers settled on an octagonal shape of the chainmail links. The best stiffness effect is achieved with circular rings and squares, which is actually the design used in ancient armors. However, these configurations are also much heavier due to the denser stacking of the links. The octagonal configuration is the most optimal one in terms of both stiffness and lighter weight.

The chainmail is made from linked octahedrons. Credit: Catech.

During one demonstration, 3-D printed polymer chainmail was compressed using a vacuum chamber or by dropping weight to control the jamming of the material. The vacuum-locked chainmail remarkably supported a load more than 50 times its weight.

When stiffened the chainmail can support 40 times its own weight. Credit: Caltech.

“Granular materials are a beautiful example of complex systems, where simple interactions at a grain scale can lead to complex behavior structurally. In this chain mail application, the ability to carry tensile loads at the grain scale is a game changer. It’s like having a string that can carry compressive loads. The ability to simulate such complex behavior opens the door to extraordinary structural design and performance,” says José E. Andrade, the George W. Housner Professor of Civil and Mechanical Engineering and Caltech’s resident expert in the modeling of granular materials.

The modern chainmail fabrics have potential applications in smart wearable clothing. “When unjammed, they are lightweight, compliant, and comfortable to wear; after the jamming transition, they become a supportive and protective layer on the wearer’s body,” says Wang, now an assistant professor at Nanyang Technological University in Singapore.

In parallel, the researchers are working on a new design consisting of strips of polymers that shrink on command when heat is present. These strips could be woven into the chainmail to create objects like bridges that fold down flat when required. The two materials joining together could use prove highly useful when incorporated into robots that can morph into different shapes and configurations.

Wooden buildings could help stabilize the climate

Replacing steel and concrete with wood could help in our efforts to stabilize the climate, a new paper reports. The shift would slash emissions generated by the production of such materials and further acts as a carbon sink.

Image via Pixabay.

Despite the advantages of using wood over other materials in construction, the findings should be taken with a grain of salt: harvesting enough timber for all buildings could place huge pressure on the environment. The authors thus caution that sustainable forest management and governance is key to the success of such a shift.

Going back to the basics

“Urbanization and population growth will create a vast demand for the construction of new housing and commercial buildings — hence the production of cement and steel will remain a major source of greenhouse gas emissions unless appropriately addressed,” says the study’s lead-author Dr. Galina Churkina from the Potsdam Institute for Climate Impact Research in Germany (PIK).

For the study, the team analyzed four different scenarios spanning thirty years into the future. The business as usual scenario considered that only 0.5% of all new buildings constructed by 2050 will be made out of timber. The second and third scenarios considered that figure to sit at 10% and 50% respectively, to simulate a mass transition towards timber. The final scenario considered that 90% of all new buildings will be constructed out of wood, simulating what would happen if even underdeveloped countries make the transition towards this building material.

The first scenario could store around 10 million tons of carbon per year, while the last would be close to 700 million tons. The team explains that reductions in cement and steel production would help further reduce emissions, which currently sit at around 11,000 million tons of carbon per year. Assuming that steel and concrete would still be in use (scenario 2 and 3) and assuming an increase in floor area per person, as has been the trend up to now, the team estimates that timber buildings could slash up to 20% of the CO2 emissions budget by 2050 by reducing emissions from building material manufacturing. The carbon budget is the quantity of CO2 emissions we can release and still meet the 2°C threshold set by the Paris agreement.

The authors argue that society needs some kind of effective CO2 sink to meet this budget to counteract hard-to-avoid emissions, such as those from agriculture. A five-story building made of laminated timber can store up to 180 kilos of carbon per square meter, they explain, which is around three times more than what a natural forest could hold. However:

“Protecting forests from unsustainable logging and a wide range of other threats is key if timber use was to be substantially increased,” explains co-author Christopher Reyer from the PIK. “Our vision for sustainable forest management and governance could indeed improve the situation for forests worldwide as they are valued more.”

Currently, the team estimates, unexploited wood resources would cover the demands of the 10% scenario. If floor area per person remains as it is now worldwide, the 50% or even 90% scenario could be feasible. An important goal here is to reduce the use of wood as fuel to free it up for use as a construction material.

Reducing the use of roundwood for fuel — currently roughly half of the roundwood harvest is burnt, also adding to emissions — would make more of it available for building with engineered timber. Moreover, re-using wood from demolished buildings can add to the supply.

“There’s quite some uncertainty involved, yet it seems very worth exploring,” says Reyer. “Additionally, plantations would be needed to cover the demand, including the cultivation of fast-growing Bamboo by small-scale landowners in tropical and subtropical regions.”

The paper “Buildings as a global carbon sink” has been published in the journal Nature Sustainability.

Microlattice pads could prevent numerous head injuries

Image credits: HRL Laboratories.

The problem with American Football players and head injuries is well-documented. Serious head injuries, including concussions and other traumatic collisions, have unfortunately become commonplace in American Football.

The helmets, as effectively as they undoubtedly are, still cannot block the damage from collisions that happen on a regular basis. However, a new technology might change that for the better.

Scientists at the University of California Santa Barbara, HRL Laboratories LLC, and the U.S. Army Research Laboratory have developed elastic microlattice pads that have remarkable physical capabilities. The lattices can withstand an impressive array of collisions — both single hits and series of impacts. When tested, the lattices seemed to perform better than existing materials.

The key to their resilience shares a similarity with the Eiffel Tower: the lattice structure is sturdy, but allows air to pass through. This means that the structure is highly adjustable and customizable, allowing engineers to tailor it to absorb different types of shock. There’s another added advantage to the design: it allows air to pass through, keeping the wearer’s head cooler.

Image credits: HRL Laboratories.

The technology is not applicable only to American Football — but to virtually to all helmets.

“Our technology could revolutionize football, batting, bicycle, and motorcycle helmets, making them better at protecting the wearer and much easier to have on your head due to the increased airflow,” says Eric Clough, a researcher at HRL Laboratories, a materials science doctoral student at the University of California, Santa Barbara, and the lead scientist on the study.

The team tested several microlattice structures. The most effective one absorbed up to 27% more energy from a single impact than the best existing polystyrene foam — the most common material in helmets. Compared to vinyl nitrile foam, another common material, it was 48% more effective. Even compared to existing microlattice designs, it absorbed 14% more energy from a single hit. Perhaps even more importantly, after the initial hit, the lattice stayed intact, ready to absorb the next round of impacts.

The results were so good they surprised the researchers themselves.

“A noticeable percentage of improvement in impact absorption was something we were hoping for, but the actual numbers were better than we expected,” says Clough. “Our testing shows that the pads work better than anything on the current market.”

The technology has already been licensed by a sports company, and the team will continue their work to see how the technology could be applied in the military.

However, Clough cautions that the technology isn’t a “magic bullet” capable of shielding the user from all head injuries — people should still be wary of injuries.

“Wearers of helmets with our padding can enjoy the benefits but should never assume they are completely protected from injury or look to test the limits of the product by possibly endangering themselves unnecessarily,” he says. “Even a great helmet can’t always protect you from every injury all the time.”

Rheometer with material.

Novel material can change under the right light, to be either strong or self-healing

A new MIT-designed polymer can both put up a tough front or show its softer side and heal — its mood changes with the ambient light.

Rheometer with material.

A rheometer, a device used to measure the mechanical properties of materials. The blue-colored gel on the stage of the instrument is the material developed by MIT.
Image credits Felice Frankel.

Materials have come a long way. Far gone are the days when we only had stones for tools and pelts to dress with — now we have fancy things like plastics, glass, metals or concrete to shape our world with. We’re also much better at processing them with high precision, which took us from shaky beds and tough-spun tunics to comfy, modern beds and comfy, modern clothing.

However, for all our advances in material science, we’ve yet to develop something that’s resilient without requiring occasional repairs. Since mending is tedious, boring, and occasionally impossible (think of a satellite in orbit), one research team from MIT decided to develop a material that takes care of that problem.

Researchers have dabbled in self-healing materials before. These efforts haven’t yet seen wide-scale applications, but they’re not exactly ‘new’ either. However, self-healing materials tend to trade resilience for their ability to repair themselves. What this new research brings to the table is a material that can be both hardy and self-healing — I say ‘both’ but it’s more of a case of ‘either/or’.

Light healing

A material’s structural strength stems from the way its constituent atoms and molecules tie to one another — a characteristic known as a material’s ‘topology’. Self-healing materials need a laxer topology with more permissive bonds in order to ebb and flow into any damaged areas. However, that also makes the end material much less resilient — which is a product of a rigid, well-knit topology.

To work around the problem, the team designed a polymer that can actually change its own topology in response to light.

“You can switch the material states back and forth, and in each of those states, the material acts as though it were a completely different material, even though it’s made of all the same components,” says Jeremiah Johnson, an associate professor of chemistry at MIT, and lead researcher of the project.

Topology is something that typically remains fixed after a material is formed. Or, if this topology is altered, it’s usually not via a reversible process. Rubber, for example, becomes brittle over time due to ozonation and oxidation (reactions with ozone and oxygen, respectively), which alter its topology.

To make the process reversible, the team worked with polymers attached to photosensitive molecules. This way, they could use light to activate and change the topology of the material.

PolyMOCs.

The design of polyMOCs with photoswitchable topology.
Image and caption credits: Yuwei Gu et al., 2018, Nature.

The team started from a class of materials they had designed previously, known as polymer metal-organic cages — or polyMOCs. The researchers describe them as metal-containing cage-like structures strewn together by flexible polymer bridges. The metal bits of the material are tied to the strands of polymer using chemical structures called ligands. Each metal atom (the team used palladium) can bind to four ligand molecules, and several of these sub-assemblies come together to create a rigid structure (the ‘cages’). The exact ratio of ligand molecules to metal atoms determines the size of the cages.

The team’s goal for the new material was to enable it to reversibly switch between two cage sizes: one with 24 atoms of palladium for 48 ligand molecules, and one with 3 palladium atoms for 6 ligand molecules.

Here’s where the photosensitive molecule DTE comes in. The ligand ties to the palladium atom via a nitrogen compound, and as most bonds in chemistry, this forms at a particular angle. The team mixed DTE into the ligand strands to act as a kind of light-operated switch that changes the angle of this bond.

When the material is exposed to ultraviolet (UV) light, this DTE molecule forms a ring and physically pushes the ligand strut away from the palladium — which alters the angle of the bond. This motion breaks apart the cages and forces them to re-form into larger ones.

By contrast, when the material is exposed to green light, that ring is broken, the ligands can tie to the palladium at a sharper angle, and the smaller cages re-form.

In the small-cage state, the material is up to 10 times softer and more dynamic than in the large-cage state, the team reports.

“They can flow when heated up, which means you could cut them and upon mild heating that damage will heal,” Johnson says.

Versatile, but short-lived

The switch takes around five hours to complete, and the team says their material can bear up to seven cycles before breaking down — with each reversal, some of the polymers fail to make the switch, which eventually results in local or wide-spread structural instability.

Still, for such an early stage, these are definitely exciting results. With some more refining, the material could serve in a wide range of applications — similar materials could coat objects such as cars or satellites, giving them a ‘skin’ that can heal damage.

“Anything made from plastic or rubber, if it could be healed when it was damaged, then it wouldn’t have to be thrown away. Maybe this approach would provide materials with longer life cycles,” Johnson adds.

Another potential application could include drug delivery. These could be encapsulated in the cages and released when exposed to UV light — then, upon exposure to green light, the same cages would recapture the substances, giving us a new way to control exactly where and when a drug is released in the body.

However, such applications are still far in the future. Apart from improving the number of cycles these materials can pass through to make them practical, the team also has to work on costs. They used polyethylene glycol (PEG) polymer, which isn’t very pricey and which should be replaceable by any kind of polymer. The real issue is the palladium, which is very rare and very expensive.

Another goal the team has set for the future is to create materials that can switch between a liquid and solid state using a similar system, and to use light to create softer and more solid sections within the same material.

The paper “Photoswitching topology in polymer networks with metal–organic cages as crosslinks” has been published in the journal Nature.

Lego will start making its first sustainable pieces, replacing plastic

Lego recently announced that they will start producing pieces from sustainable sugar cane. The toys, which will be indistinguishable from classic Legos, will also feature “botanical elements” like leaves, bushes, and trees. Lego’s current bricks are made from oil-based plastics.

“We want to make a positive impact on the world around us, and are working hard to make great play products for children using sustainable materials,” said Tim Brooks, vice president, environmental responsibility at the Lego Group, in a statement. “This is a great first step in our ambitious commitment of making all Lego bricks using sustainable materials.”

The new line of production has reportedly already started with pieces being produced from polyethylene, which is a soft, durable and flexible plastic — technically identical to those produced using conventional plastic. Lego says that we needn’t worry about the quality of the new products, as they’ve tested the plant-based plastic to ensure that it meets the high standards for quality and safety that consumers expect from the company.

“LEGO products have always been about providing high quality play experiences giving every child the chance to shape their own world through inventive play. Children and parents will not notice any difference in the quality or appearance of the new elements, because plant-based polyethylene has the same properties as conventional polyethylene,” said Tim Brooks.

The move is part of Lego’s campaign to use sustainable materials in its core products and packaging by 2030, a move in which they have already invested $165 million. According to a research report, 4% of the world’s petroleum is used as a raw material to make plastic, and another 4% is used in the plastic-making process. Since plastic is so ubiquitous and so notoriously non-eco-friendly, finding ways to replace it is extremely important. With this in mind, Lego has partnered with WWF to play their part, joining the Bioplastic Feedstock Alliance (BFA), which supports the responsible development of plastics made from plant material.

“It is essential that companies in each industry find ways to responsibly source their product materials and help ensure a future where people, nature, and the economy thrive,” said Alix Grabowski, a senior program officer at WWF. “The LEGO Group’s decision to pursue sustainably sourced bio-based plastics represents an incredible opportunity to reduce dependence on finite resources, and their work with the Bioplastic Feedstock Alliance will allow them to connect with other companies to continue to think creatively about sustainability.”

Superdense wood.

Strong as steel and lightweight? Must be superdense wood

American researchers are giving the term hardwood a whole new meaning. They have developed a relatively simple, boil-and-crush technique to make “superdense” wood — a strong but lightweight material which could be used to build everything from bridges to cars.

Superdense wood.

The wood-compacting process crushes gaps between cell walls in natural wood seen in the scanning electron microscopy image on the left), making densified wood (right) as strong as steel.
Image credits J. Song et al., Nature, 2018.

People have built and crafted with wood since times immemorial, and for good reason: it’s a plentiful, cheap, readily available building material (in most parts of the world), it’s got a good blend of strength and flexibility, and it’s relatively easy to work with. It also, to me at least, looks quite nice. Our relationship with wood as a building material, however, started to taper out with the industrial revolution, and today, it’s more of an occasional fling on the side than anything serious.

Old log, new tricks

Which is actually quite sad, as although wood lagged behind in the “strength” department, all its other qualities are still there. In a bid to put the spark back in this old flame, a team of US researchers has developed superdense wood — a highly-compacted wood that’s about as strong as steel, but much more lightweight.

The enviable physical properties of this material can be traced back to its production. It is constructed by boiling regular blocks of wood in a water-based solution of sodium hydroxide (lye) and sodium sulfite. These chemicals remove part of the lignin and hemicellulose in the wood (two organic compounds that give wood its structure and rigidity), making it more malleable.

This limbered-up lumber is then pressed at 5 megapascals (50 times the atmospheric pressure at sea-level) between two metal plates heated to 100° Celsius (212° F). The process squishes all the gaps between cells in the wood, shrinking the block to about 20% its initial thickness and increasing density three-fold.

With great squish comes great power, however: mechanical testing revealed that ultradense wood produced in this manner can withstand being stretched or pulled 11.5 times harder than the original without breaking. This would make it comparable to steel in strength, although it’s also more lightweight. The team also tested typical and superdense wood planks against stainless steel pellets fired from an airgun at 30 meters (98.5 feet) per second. The pellets went clean through the natural wood, but got lodged in the stack of densified wood of the same thickness, as you can see below:

Another advantage of the process, notes co-author Teng Li, a mechanical engineer at the University of Maryland in College Park, is that the chemicals used to scrub lignin and hemicellulose from the wood won’t pose any significant pollution concerns. In light of that fact, and of wood’s comparatively low environmental impact and sustainability, superdense wood could become an eco-friendly alternative to steel or other metallic alloys for construction works. Alternatively, it could be used in the manufacturing of more light-weight, more fuel-efficient vehicles, he adds.

As a final morsel for thought: wood is, ultimately, a form of carbon storage — plants, after all, scrub carbon from the atmosphere to grow. Viewed in this light, using superdense wood as a building material on a wide scale could help us hit two birds with one stone (if it’s harvested sustainably, of course). On one hand, it would help reduce carbon emissions from metal and non-metal mining and refining. On the other, it would capture some of the CO2 that’s already floating around. We can even make the window panes out of wood!

With the climate woes we’re facing, and those waiting for us in the future, we’ve got very few such stones to throw — and we need to get as many birds as we can.

The paper “Processing bulk natural wood into a high-performance structural material” has been published in the journal Nature.

Islamic art inspires metamaterial that grows when stretched

A new type of metamaterial that can grow when stretched, with possible applications for medical equipment and satellites, was inspired by an unlikely source — ancient Islamic art.

Most materials, such as cotton, plastic or rubber, stretch in one direction and become thinner in another when you pull on them. Some metamaterials however, a class of materials engineered specifically to have properties that don’t occur naturally, can be designed to grow as you pull on them.

It all comes down to the way they’re structured at a microscopic level. If you zoom in enough, you’ll see that they’re typically made up of a series of interconnected squares. When pulled apart, these squares turn relative to one another, increasing the total volume of the material — in essence, becoming larger. But this comes at the price of losing the original shape of the material as it expands.

Ahmad Rafsanjani and Damiano Pasini of McGill University in Montreal, Canada, set out to create a material that would grow when stretched but keeps its form. And they turned to the beautifully intricate geometry of ancient Islamic arhitecture.

Some of the designs that the team used as inspiration.
Image credits A Rafsanjani/McGill University.

 

“There is a huge library of geometries when you look at Islamic architectures,” says Rafsanjani.

The team picked their designs out of the over 70 patterns adorning the walls of Iran’s Kharragan towers, two mausoleums built in 1067 and 1093 in the northern part of the country. The mausoleums are decorated with intricate patterns of both repeating and alternating shapes, separated by either parallel or circular cuts.

Based on the same design features, the team fashioned the new metamaterial from natural rubber. When pulled on, it can expand into a larger volume that the original by leaving open spaces in between the shapes.

“I introduced some cuts and some hinges, but the pattern is exactly the same,” says Rafsanjani.

The new material, based on designs nearly a thousand years old.
Image credits A Rafsanjani/McGill University

Rafsanjani presented the materials at a meeting of the American Physical Society in Baltimore, Maryland, on 15 March.

The ability of the material could make it useful for an array of applications, such as inserting medical devices inside veins and arteries, or deploying new satellites that unfold in space.

Mantis shrimps teach humans how to make a new type of optical material

Some time ago we wrote about the mantis shrimp’s uncanny form of communication: polarized light. Research focusing in on these tiny animals’ chatter will allow us to create a whole new type of polarizer — an optical device widely employed in modern cameras, DVD players, even sunglasses.

Mantis shrimp are probably best known for the dazzling colors that adorn their shells. The second thing they’re best known for is their tendency to violently murder anything they come into contact with. Using two frontal appendages that can move as fast as a bullet, the shrimp hunts for crabs, oysters, octopi, anything really, blasting them apart with an insanely powerful 1,5 kilo Newtons of force (337.21 lbs of force.)

Look at him. He just knows he’s the baddest shrimp in this pond.
Image via wikipedia

But why? And how did they come by their weapons? What is the mantis shrimp’s secret? Well nobody knows, because they communicate using a process so secretive most other species don’t even realize it’s happening.

The shrimp rely on light polarization to keep their conversations private. They have evolved reflectors that allow them to control the polarization of their visual signals, a property of light that most other species aren’t able to pick up on.

In an effort to crack their code, researchers from the Ecology of Vision Group (based in the University of Bristol’s School of Biological Sciences) have studied the shrimps and discovered they employ a polarizing structure radically different from anything that humans have ever seen or developed.

The team’s analysis, coupled with computer modelling revealed that the mantis shrimp’s polarizers manipulate light across it’s structure rather than through its depth — as our polarizers do. This mechanism allows the animal to have small, microscopically thin and dynamic optical structures that still produce big, bright and colourful polarized signals.

“When it comes to developing a new way to make polarizers, nature has come up with optical solutions we haven’t yet thought of,” said Dr Nicholas Roberts from the School of Biological Sciences.

“Industries working on optical technologies will be interested in this new solution mantis shrimp have found to create a polarizer as new ways for humans to use and control light are developed.”

The full paper, titled ‘A shape-anisotropic reflective polarizer in a stomatopod crustacean’ is available online here.

microlattice

World’s lightest material is 99% air

The rest of the 1% is made up of hallow tubes of nickel. So, this makes for a very rigid, but extremely lightweight material. Just look at the picture below of the lightest material in the world, called microlattice, balancing on a dandelion. You know the potential is huge.

microlattice

Credit: HRL Laboratories

Microlattice was first developed in 2011, a joint effort by researchers from HRL, CalTech and the University of California, Irvine. Now, Boeing – the company who mainly funded the research – released an entertaining video presenting the work.

Sophia Yang, a research scientist at HRL Laboratories says they were inspired by human bones, which are very rigid on the outside, but very porous and mostly filled with air inside. This makes bones hard to break, but also lessens the strain on the muscles which have to carry all the load. Microlattice works similarly, only at a much higher tensile compression thanks to its  hollow tubes just 100 nanometers across. This allowed for 99% open volume, all filled with air, which can absorb a lot of energy. If you were to crush it even more than halfway through, it would just bounce back to its initial size and shape.

Microlattice has a density of only 0.9 milligrams per cubic centimetre. Silica aerogels – the world’s lightest solid materials – have a density as low as 1.0mg per cubic cm. But whereas the structure of aerogel is mostly chaotic, microlattice has an orderly lattice structure which makes it a lot stiffer and stronger. Structure maters a lot. Just look at how weight efficient and versatile structures like the Eiffel Tower or the Golden Gate Bridge are.

Microlattice could become useful in aerospace applications, lowering the weight of aicraft, hence boosting fuel savings. It could also be used as battery electrodes, shock or acoustic absorber, construction material and so on.

Scientists find highest melting point ever

Using computer simulations, Brown University researchers identified the material with the highest known melting point. The material, made with just the right amount of hafnium, nitrogen, and carbon would have a melting point of more than 4,400 kelvins (7,460 degrees Fahrenheit). That’s almost as high as the temperature at the surface of the Sun, and more than the highest temperature ever achieved by humans.

Pictured above, hafnium was a key element in the mixture. Picture credits: Images of Elements.

The melting point is pretty much what the name says: the temperature at which a solid becomes liquid at atmospheric pressure; at exactly the melting point, the solid and liquid phases exist in equilibrium.

Mixing different materials together dramatically changes the melting point, but predicting what materials will have the highest melting point is like looking for a needle in a hay stack – this is why researchers didn’t just blindly start mixing substances.

“The advantage of starting with the computational approach is we can try lots of different combinations very cheaply and find ones that might be worth experimenting with in the lab,” said Axel van de Walle, associate professor of engineering and co-author of the study with postdoctoral researcher Qijun Hong. “Otherwise we’d just be shooting in the dark. Now we know we have something that’s worth a try.”

The technique they used analyzes the melting dynamics on a small scale, in blocks of 100 or so atoms. The technique is more efficient than traditional methods, but requires massive computational resources.

Having materials with high melting points is crucial in a number of industries, from plating for gas turbines to heat shields on high-speed aircraft. But researchers won’t know if the material is actually a useful one until they create it – and that’s the next step. There are other properties worth considering.

“Melting point isn’t the only property that’s important [in material applications],” he said. “You would need to consider things like mechanical properties and oxidation resistance and all sorts of other properties. So taking those things into account you may want to mix other things with this that might lower the melting point. But since you’re already starting so high, you have more leeway to adjust other properties. So I think this gives people an idea of what can be done.”

Limpet Teeth May Be World’s Strongest Material

According to a new study, limpet teeth may be the strongest material known to man, stronger than spider silk or kevlar. The potential applications for use are virtually endless, especially as the strength isn’t affected by the material’s size.

Surprising news: limpet teeth may be the world’s strongest material. Image via I Love Shelling.

“Limpet” is a common name given to aquatic snails with shells broadly conical in shape. It’s not necessarily a scientific term, and it’s used out of convenience to describe any gastropod whose shell has no obvious coiling. Researchers from the University of Portsmouth have discovered that limpets have incredibly strong teeth – they may actually be the strongest material in the world.

Professor Asa Barber from the University’s School of Engineering led the study. He said:

“Nature is a wonderful source of inspiration for structures that have excellent mechanical properties. All the things we observe around us, such as trees, the shells of sea creatures and the limpet teeth studied in this work, have evolved to be effective at what they do. Until now we thought that spider silk was the strongest biological material because of its super-strength and potential applications in everything from bullet-proof vests to computer electronics but now we have discovered that limpet teeth exhibit a strength that is potentially higher.”

Limpets need the high-strength teeth to cling on to rock surfaces and remove algae for feed when the tide is in. For this study, researchers used atomic force microscopy to test the strength of the teeth. Atomic force microscopy is a very high-resolution type of scanning probe microscopy, with a resolution on the order of fractions of a nanometer, much higher than optic microscopy.

They found that the teeth contain a mineral called goethite – an iron bearing hydroxide mineral. Goethite isn’t particularly strong, but goethite fibers are laced through a protein base in much the same way as carbon fibres can be used to strengthen plastic. The mineral forms as the limpet grows, but the strength of the teeth didn’t seem impacted by the limpets’ age.

A scanning electron microscope image of limpet teeth. Image credits: Portsmouth University.

“Limpets need high strength teeth to rasp over rock surfaces and remove algae for feeding when the tide is in. We discovered that the fibres of goethite are just the right size to make up a resilient composite structure. This discovery means that the fibrous structures found in limpet teeth could be mimicked and used in high-performance engineering applications such as Formula 1 racing cars, the hulls of boats and aircraft structures. Engineers are always interested in making these structures stronger to improve their performance or lighter so they use less material.”

Indeed, the applications for such a strong material are basically endless – strong materials are needed in most industries, from computer electronics to the car and plane industries, strong materials are a godsend. But what makes it even more spectacular and more applicable to industry is the fact that the material’s strength is not dependent on its size – in other words, you can scale it up or make it as tiny as you want.

“Generally a big structure has lots of flaws and can break more easily than a smaller structure, which has fewer flaws and is stronger. The problem is that most structures have to be fairly big so they’re weaker than we would like. Limpet teeth break this rule as their strength is the same no matter what the size.”

The tooth fragments were milled into a microscopic dog-bone shape and glued to a lever for testing.

The material the team tested in the lab was approximately 100 times thinner than a human hair. For future studies, they will have to apply more tests under more sizes and see what factors can further amplify (or threaten) the material’s strength. So far, the shape seems to be very important.

“The testing methods were important as we needed to break the limpet tooth. The whole tooth is slightly less than a millimetre long but is curved, so the strength is dependent on both the shape of the tooth and the material. We wanted to understand the material strength only so we had to cut out a smaller volume of material out of the curved tooth structure.”

It will be quite a while before we actually start seeing practical applications for limpet teeth, but the fact that scientists found such a strong material in an unexpected place is definitely thrilling and opens new perspectives.

The research was published today in the Royal Society journal Interface.

Adding water to solids can actually make them stronger, providing engineers with exciting new material composites

Some findings are just counterintuitive. I mean, you’d think that adding water to materials would always make them softer, right ? Well according to Yale researchers, that’s not necessarily the case. The team found that you could improve the strength of a composite by 30 percent by embedding droplets of water into its structure.

Scientists can make composite materials stronger by up to 30 percent by embedding water. Image credits: The Speaker.

Adding pockets of water to solids can actually make them stronger, offering new perspective in engineering, especially in plastic engineering (the technique doesn’t work with metals, ceramics or other structural materials). Engineers will also be able to add other properties (such as electromagnetism) to materials by embedding droplets of liquid. By understanding the interaction between water and other materials, researchers can also develop other, more advanced materials in the future.

“This is a great example of how different types of physics emerge at different scales,” Dr. Eric Dufresne, associate professor of mechanical engineering and materials science at Yale and principle investigator of the study, told The Speaker. “Shrinking the scale of an object can really change how it behaves.”

 Usually, embedding liquids (especially water) into the structure of another material makes the entire structure weaker, not stronger. However, as this research showed, surface tension could sometimes turn things around. Surface tension is the tension of the surface film of a liquid caused by the attraction of the particles in the surface layer by the bulk of the liquid, which tends to minimize surface area.a contractive tendency of the surface of a liquid that allows it to resist an external force.
“Surface tension is a force that tries to reduce the surface area of a material,” Dufresne said. “It is familiar in fluids–it’s the force that pulls water into a sponge, makes wet hair clump together and lets insects walk on water. Solids have surface tension too, but usually the ‘elastic force’ of the solid is so strong that surface tension doesn’t have much of an effect. The ‘elastic force’ of a solid is what makes a solid spring back to its original shape after you stop pushing on it.”
Duresfne called this technology “a new knob to turn” for engineers, who can now have more control over the properties they choose to include in their materials – these properties can be mechanical, electrical and even optical.
“As the solid gets stiffer, the liquid droplets need to be smaller in order to have this stiffening or cloaking effect. By embedding the solid with droplets of different materials, one can give it new electrical, optical or mechanical properties. On the simple scale, they could lower the cost be replacing expensive polymers with simple liquids. More excitingly, embedded droplets could provide an electromagnetic handle to actuate structures.”

Journal Reference: Robert W. Style, Rostislav Boltyanskiy, Benjamin Allen, Katharine E. Jensen, Henry P. Foote, John S. Wettlaufer, and Eric R. Dufresne. Stiffening solids with liquid inclusions.

Wonder material graphene can be made magnetic – and turned on and off

Is there something that graphene can’t do? It’s the world’s strongest material, even when it has flaws, a graphene aerogel is also the lightest material known, it’s great for sensors, for headphones, it repairs itself, and boasts a swarm of other features and capabilities. Now, researchers from Manchester University have shown that they can create elementary magnetic moments in graphene and then switch them on and off.

graphene magnetism

This is the first time, with any material, that magnetization was swtiched on and off, instead of on and then reversed – which makes the prospects even more intriguing.

Modern society is so dependent on magnetic materials we can’t even imagine the world without them. Everything we do depends on them – be it hard disks, memory chips, or airplane navigation. When it comes to graphene, its magnetism is a little unconventional – whenever atoms are removed from its lattice, microscopic holes called vacancies appear – the physicists from Manchester have shown that electrons condense around these holes into small electronic clouds; each of these clouds behaves like a microscopic magnet carrying one unit of magnetism, spin. Dr Irina Grigorieva and her team have shown how to turn this magnetism on and off.

“This breakthrough allows us to work towards transistor-like devices in which information is written down by switching graphene between its magnetic and non-magnetic states. These states can be read out either in the conventional manner by pushing an electric current through or, even better, by using a spin flow. Such transistors have been a holy grail of spintronics.”

Dr Rahul Nair, who was in charge of the experimental effort, explained why this is such a big deal:

“Previously, one could only change a direction in which a magnet is magnetized from north to south. Now we can switch on and off the magnetism entirely. Graphene already attracts interest in terms of spintronics applications, and I hope that the latest discovery will make it a frontrunner.”

Nobel Laureate and co-author of the paper Professor Andre Geim, who discovered graphene as a material concluded there is much reason for optimism:

“I wonder how many more surprises graphene keeps in store. This one has come out of the blue. We have to wait and see for a few years but the switchable magnetism may lead to an impact exceeding most optimistic expectations.”

Scientists use lasers to unravel mysterious spider silk strength

Pound for pound, spider silk is one of the strongest materials in the world; it’s about five times stronger than a piano wire – and a piano wire has to put up with a lot of pressure. Researchers have long tried to develop materials which mimic the remarkable properties of spider silk, but only now did Arizona scientists announce that they are able to obtain a wide variety of elastic properties of the silk of several intact spiders’ webs using a sophisticated laser light scattering technique.

spider silk

“Spider silk has a unique combination of mechanical strength and elasticity that make it one of the toughest materials we know,” said lead researcher Jeffery Yarger of Arizona State University’s Department of Chemistry and Biochemistry, in a statement. “This work represents the most complete understanding we have of the underlying mechanical properties of spider silks.”

Scientists used extremely low power lasers (less than 3.5 milliwats) and aimed it at spider webs. Using this novel approach, they were able to actually map the stiffness of each web without disturbing it; they found variations among discreet fibers, junctions, and glue spots.

They studied webs from four different spider species: Nephila clavipes, A. aurantia (gilded silver face), L. Hesperus (western black widow) and P. viridans (green lynx spider) – all with remarkable silk properties. But they didn’t only study the stiffness, they also studied a property that spider silk displays, called supercontraction – a property unique to spider silk. Basically, it soaks up water when exposed to high humidity, and this absorbed water can lead to shrinkage in an unrestrained fiber-up to 50 percent. However, even in these conditions, spider silk is still versatile, and supercontraction helps the spider tailor the actual properties of the silk it produces during spinning.

“This study is unique in that we can extract all the elastic properties of spider silk that cannot and have not been measured with conventional testing,” said Yarger.

This new study could pave the way for new biomaterials to create tronger, stretchier, and more elastic materials.

The study was published in Nature Materials.