Archive for the ‘materials science’ Category

Researchers make a robotic fish with a battery for blood

June 19th, 2019
Image of a plastic fish

Enlarge (credit: James Pikul)

Lots of experimental robots involve a little bit of cheating. Rather than containing all the necessary electronics and energy sources, they have tethers and wires that provide power and control without weighing the robot down or taking up too much internal space. This is especially true for soft-bodied robots, which typically pump air or fluids to drive their motion. Having to incorporate a power source, pumps, and a reservoir of gas or liquid would significantly increase the weight and complexity of the robot.

A team from Cornell University has now demonstrated a clever twist that cuts down on the weight and density of all of this by figuring out how to get one of the materials to perform two functions. Like other soft robot designs, it pumps a fluid to cause its structure to expand and contract, powering movements. But in this case, the fluid is also the key component of a flow battery that powers the pumps. This allows them to put all the critical components on board their creation.

Going with the flow

So what's a flow battery? Batteries operate by having different reactions that take place at their two electrodes. For something like a lithium-ion battery, the intermediaries of these reactions—electrons and ions—immediately flow from one electrode to another, and the key chemicals spend almost all their time at the electrodes. In flow batteries, the chemical reactions still take place at the electrodes, but the chemicals reside in solution, rather than being confined to electrodes.

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Posted in batteries, fish, materials science, Robotics, science | Comments (0)

Atomically thin material could cut need for transistors in half

May 28th, 2019

With the development of carbon nanotubes and graphene, scientists were given an entirely new collection of materials to work with: sheets and tubes that could be consistently made with thicknesses roughly those of individual atoms. These materials hold the promise of building electronic devices with dimensions smaller than is currently possible through any other process and with properties that can be tuned by using different starting materials.

So far, most of the attention has gone to re-creating new versions of familiar devices. But a new paper by a group of researchers in Shanghai looks into what can be done if you're not constrained by the sorts of devices we currently make in silicon. The result is a device that can perform basic logic in half the transistors silicon needs, can be switched between different logical operations using light, and can store the output of the operation in the device itself.

OR or AND?

Computer instructions can be distilled down to a series of simple logical operations. Of theses, the simplest are AND and OR. AND produces a value of 1 only if both of its two inputs are also 1; OR does so if either of the two inputs are 1.

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Posted in atomically thin materials, chips, logical operations, materials science, science, silicon | Comments (0)

Stronger than aluminum, a heavily altered wood cools passively

May 23rd, 2019
Image of a white plank.

Enlarge / A look at the lignin-free compressed wood. (credit: University of Maryland)

Most of our building practices aren't especially sustainable. Concrete production is a major source of carbon emissions, and steel production is very resource intensive. Once completed, heating and cooling buildings becomes a major energy sink. There are various ideas on how to handle each of these issues, like variations on concrete's chemical formula or passive cooling schemes.

But now, a large team of US researchers has found a single solution that appears to manage everything using a sustainable material that both reflects sunlight and radiates away excess heat. The miracle material? Wood. Or a form of wood that's been treated to remove one of its two main components.

With the grain

Wood is mostly a composite of two polymers. One of these, cellulose, is made by linking sugars together into long chains. That cellulose is mixed with a polymer called lignin, which is not really a single polymer. The precise chemical formula of its starting material can vary among species, and it typically contains multiple places where chemical bonds can form, turning the polymer into a chaotic but extremely robust mesh.

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Posted in chemistry, materials science, science, sustainability, wood | Comments (0)

Science and bicycling meet in a new helmet design

April 14th, 2019
Image of a bike helmet cutaway to reveal a green mesh underneath.

Enlarge (credit: Trek)

When we recently did an overview of the evolution of bicycling technology, helmets were barely mentioned. They've been made out of the same materials for decades, and the only improvement they've seen in that time is a more efficient venting layout. But the timing of that article turned out to be propitious because, a few months later, Trek got in touch to let me know it was introducing the first major change in helmet technology in years.

Normally, emails like that are little more than marketing, or failing that, everything's proprietary and can't be talked about. But in this case, Trek promised that there was peer-reviewed science behind the announcement and I'd get the chance to talk to the scientists themselves. A few weeks later, I got the chance to check out the helmets and meet the scientists (though I narrowly missed my chance to shake hands with cycling legend Jens Voigt).

What’s a helmet actually do?

The obvious answer is that helmets are meant to protect your brain when your head experiences an impact. But the more detailed answer requires delving into a little bit of physics. On a simple level, an impact generates force that, if nothing is protecting you, is translated directly to your skull. A helmet's job is to dissipate that force. If a helmet could be arbitrarily large or heavy, this would not be a problem. But cyclists are notoriously picky about their equipment's weight and aerodynamics, which means that a helmet has to do all its redirection of forces in as little space as possible, using light materials.

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Posted in bicycles, head injuries, helmets, materials science, medicine, science | Comments (0)

MIT scientists: Heat can act like sound wave when moving through pencil lead

March 16th, 2019
Pile of tiny gray rods.

Enlarge / Graphite rods ready to be encased in wood to make pencils. MIT scientists have shown that heat behaves like sound when moving through graphite. (credit: Jean-Christophe Verhaegen/AFP/Getty Images)

A boiling tea kettle diffuses its heat to gradually warm surrounding air, yet it will still be the warmest region even as it, too, slowly cools. But what if the kettle cooled down to room temperature almost instantly, losing its heat in a wave traveling through the material close to the speed of sound? MIT researchers have observed this rare, counterintuitive phenomenon—known as "second sound"—in graphite, the stuff of pencil lead. They described their results in a paper published earlier this week in Science.

Chances are you've never heard of the concept of "second sound," even though the phenomenon has been known for decades. "It's been confined to only a handful of materials that are really very low temperature," said co-author Keith Nelson, severely limiting its potential usefulness. There might be a paragraph or two on the topic in your average solid-state textbook, but the field "has been kind of a backwater."

With the results of this new research, that may be about to change. Graphite is a very common material, and the effect was observed at a relatively balmy (by low-temperature physics standards) temperature of around -240 degrees F. The team's theoretical models indicate it might be possible to produce the effect in graphene at something closer to room temperature in the future, thereby opening up any number of potential practical applications. For instance, microelectronics just keep getting smaller, making heat management a daunting challenge. If room-temperature graphene could rapidly carry off heat as waves, it might allow even more miniaturization.

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Posted in graphene, graphite, materials science, Physics, science, sound | Comments (0)

New fuel cell material can run efficiently in reverse, storing energy

March 14th, 2019
Close-up of a hydrogen fuel cell.

Enlarge / Close-up of a hydrogen fuel cell. (credit: Wladimir Bulgar | Science Photo Library)

Lithium batteries can readily smooth out short-term hiccups in the supply of intermittent renewable energy. But they're not ideal for long-term storage, since they'll slowly discharge. They also aren't great for large quantities of energy—to store more, you keep having to buy more battery. Because of these issues, there has been research into a number of technologies that scale better, like flow batteries and renewable fuel production. But these pose their own challenges, both chemical and economic.

But researchers are now reporting a possible solution to some of these problems: a fuel cell that can be run efficiently in both directions, either using hydrogen or methane to produce electricity or using electricity to produce these fuels. Their measurements suggest that, after doing a complete cycle, they get out 75 percent of the electricity they put in to start with.

Limitations abound

Batteries, as we mentioned above, don't work for longer-term storage, as they will typically lose charge slowly. They're also expensive, as adding capacity means adding more batteries. Flow batteries solve some of these problems by storing the charged and discharged forms of a chemical in different tanks; larger or additional tanks are cheap, making expanded capacity relatively simple and inexpensive. But flow batteries aren't as efficient as traditional batteries, and the chemicals they use can be toxic or corrosive.

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Posted in chemistry, Energy, fuel cells, hydrogen, materials science, science | Comments (0)

Physicists are decoding math-y secrets of knitting to make bespoke materials

March 8th, 2019
Introducing topological defects into knitted patterns can shape the (a) out-of-plane elasticity of a stuffed rabbit (left), and (b) the in-plane deformations of knitted textiles (right).

Enlarge / Introducing topological defects into knitted patterns can shape the (a) out-of-plane elasticity of a stuffed rabbit (left), and (b) the in-plane deformations of knitted textiles (right). (credit: Elisabetta Matsumoto)

Knitted fabrics like a scarf or socks are highly elastic, capable of stretching as much as twice their length, but individual strands of yarn hardly stretch at all. It's the way those strands form an interlocking network of stitches that give knitted fabrics their stretchiness. Physicists are trying to unlock the knitting "code"—the underlying mathematical rules that govern how different stitch combinations give rise to different properties, like stretchiness—in hopes of creating new "tunable" materials whose properties can be tailored for specific purposes.

"Knitting is this incredibly complex way of converting one-dimensional yarn into complex fabric," said Elisabetta Matsumoto, a physicist at the Georgia Institute of Technology. "So basically this is a type of coding." Figuring out how different stitch types determine shape and mechanical strength could help create designer materials for future technologies—everything from better materials for the aerospace industry to making stretchable materials to replace torn ligaments. The models her team is developing may also be useful in improving the realistic animation of clothing and hair in computer game graphics. Matsumoto described her research during the American Physical Society's 2019 March meeting taking place this week in Boston.

Knitted fabrics can technically be considered a type of metamaterial (engineered materials that get their properties not from the base materials, but from their designed structures), according to Matsumoto, who points to the medieval embroidery technique known as "smocking" as an early example. From a physics standpoint, smocking uses knots to essentially convert local bending energy into bulk stretching energy.

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Posted in geometry, knitting, materials science, mathematics, Physics, science, topology | Comments (0)

Researchers make RAM from a phase change we don’t entirely understand

December 18th, 2018
Illustration of atoms.

Enlarge / Two layers of one of the materials used in this work. (credit: The American Mineralogist Crystal Structure Database)

We seem to be on the cusp of a revolution in storage. Various technologies have been demonstrated that have speed approaching that of current RAM chips but can hold on to the memory when the power shuts off—all without the long-term degradation that flash experiences. Some of these, like phase-change memory and Intel's Optane, have even made it to market. But, so far at least, issues with price and capacity have kept them from widespread adoption.

But that hasn't discouraged researchers from continuing to look for the next greatest thing. In this week's edition, a joint NIST-Purdue University team has used a material that can form atomically thin sheets to make a new form of resistance-based memory. This material can be written in nanoseconds and hold on to that memory without power. The memory appears to work via a fundamentally different mechanism from previous resistance-RAM technologies, but there's a small hitch: we're not actually sure how it works.

The persistence of memristors

There is a series of partly overlapping memory storage technologies that are based on changes in electrical resistance. These are sometimes termed ReRAM and can include memristors. The basic idea is that a material can hold a bit that is read based on whether the electrical resistance is high or whether electrons flow through like it was a metal. In some of these, the resistance can be set across a spectrum that can be divided up, potentially allowing a single piece of material to hold more than one bit.

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Posted in materials science, reram, Resistance, science | Comments (0)

Fractal structure produces fractal electrons with fractal energies

December 2nd, 2018

Fractals are a source of endless fascination to me. Life itself relies on many of the concepts of fractals: trees are fractal, as are feathers, coast lines, and many other things in nature. Indeed, it was the realization that landscapes are fractal that made modern animated films possible.

But, what about fractional dimensions in quantum mechanics? It turns out that electrons in a Sierpiński gasket are also fractal, and that has some pretty cool consequences.

A fractal is a weird beast. A line is 1D, a square is 2D, and a cube is 3D: dimensions come in integer quantities. Except they don't. For instance, it is possible to create a shape that has a finite area, but a perimeter that is infinitely long (the construction of such a shape is pictured below). A shape with these properties does not behave like a 2D object, but it's not a 3D object. Instead, it is a two-and-a-bit-D object. That is a fractal.

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Posted in electron wave function, fractals, materials science, Physics, science | Comments (0)

High-density lithium in graphene: An intriguing battery possibility

November 29th, 2018
High-density lithium in graphene: An intriguing battery possibility

Enlarge (credit: Getty Images)

Discussions about batteries often revolve around energy density. What we want is a battery that stores a whole lot of energy in a very tiny volume, preferably in a manner that doesn't involve explosions or fire. At the cutting edge of research, what we get are batteries that are a mix of amazing and amazingly bad.

Modern batteries are, quite frankly, a miracle compared to ye olde lead acid battery. Yet they still contain less energy per unit mass than the equivalent mass of wood. Essentially, we simply don’t pack enough atoms into a small enough volume to compete with hydrocarbons. But, now it seems that graphene—it’s always graphene—might help pack lithium in.

The invisible metal

Although there are many ways to make a lithium-ion battery, the chemistry boils down to the following: lithium is stored in some form at one electrode. The lithium is released as an ion, where it travels to another electrode and reacts. At the same time, the electrons that complete the reaction travel out into the world via one electrode, do some work, and end up at the other electrode, where they complete the reaction.

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Posted in graphene, lithium-ion batteries, materials science, science, transmission electron microscope | Comments (0)