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Posts Tagged ‘carbon nanotubes’

Traditional cables are made by braiding or twisting together two or more wires or optical fibers, usually metal or silicon, to carry a current or signal. In a new study, Rice University researchers instead used double-walled carbon nanotubes, made of concentric rolled-up sheets of graphene.

To make the cable, the team grew billions of nanotubes and spun them with a polymer into tiny wires just a few centimeters long. The wires were doped with iodine to keep them stable, and then they could be tied together without compromising their conductivity, according to a Rice news release. The resulting cable is corrosion-resistant and is much lighter and less dense than copper. Its conductivity-to-weight ratio, known as specific conductivity, is better than copper and silver — it’s second only to sodium in the suite of metals with the highest specific conductivity, the researchers say.

To prove it worked, Rice doctoral student Yao Zhao built a circuit that directed power through the nanocable, replacing copper wire. He turned on a CFL bulb and let it shine for several days, and saw no signs of degradation in the nanocable. Tests showed it would be just as strong and durable as copper, and would work in a wide range of temperatures, the team says.

The next step is to make longer, thicker cables that can carry a greater current, according to Enrique Barrera, a Rice professor of mechanical engineering and materials science. The nanocables could someday be used in aircraft, spacecraft and cars, and could someday even replace electrical wiring in homes, the team says. Barrera and Zhao explain the technique in the video below.

The work appears in the journal Nature Scientific Reports.

[via PhysOrg]

Without getting too deeply into the history of stretchable (and bendable) OLEDs, it seems that the major struggle with stretchable OLEDs is finding a way to maintain conductivity while the panel is being wrenched around. These UCLA researchers used carbon nanotubes, which are stretchable but tend to have difficulty maintaining their shape. Says Technology Review:

To make their device entirely pliable, the UCLA researchers devised a novel way of creating a carbon nanotube and polymer electrode and layering it onto a stretchable, light-emitting plastic. To make the blended electrode, the team coated carbon nanotubes onto a glass backing and added a liquid polymer that becomes solid yet stretchable when exposed to ultraviolet light. The polymer diffuses throughout the carbon nanotube network and dries to a flexible plastic that completely surrounds the network rather than just resting alongside it. Peeling the polymer-and-carbon-nanotube mix off of the glass yields a smooth, stretchable, transparent electrode.

The end product is essentially two layers of that carbon nanotube electrode with that particular type of plastic in the middle. Interestingly, the team actually used a regular office laminator to press the layers together and squeeze out any air bubbles. What they ended up with was a display that emits a blue light even when stretched by as much as 45%.

This is definitely just a first step towards our sci-fi dream displays (like, OLED clothing, or a phone that we can stretch into a tablet) but the process is simple enough that researchers should be able to build on it until we get to that point.

The full report was published in this month's Advanced Materials.

[via PhysOrg]

In tests, their synapse circuit functions very much like a real neuron--neurons being the very building blocks of the brain. Tapping the unique properties of carbon nanotubes, their lab was able to essentially recreate brain function in a very fractional way.

Of course, duplicating synapse firings in a nanotube circuit and creating synthetic brain function are two very different things. The human brain, as we well know, is very complex and hardly static like the inner workings of a computer. Over time it makes new connections, adapts to changes, and produces new neurons.

But while a functioning synthetic brain may be decades away, the synthetic synapse is here now, which could help researchers model neuron communications and otherwise begin building, from the ground up, an artificial mimic of one of biology’s biggest mysteries.

Normally, viscoelastic materials, like foam earplugs and mattresses, perform well in moderate temperatures — but they break down when they get too hot and harden when they get too cold. Silicone rubber hardens into glass around 575 degrees F, for instance. The new material deforms under extreme temperatures, but it maintains its strength and quickly recovers its shape. To test its mettle, the researchers let it sit at room temperature, blasted it with a butane torch and froze it with liquid nitrogen. It withstands temperatures from –320 F to 1,832 F, according to the study, which is published today in the journal Science.

This exceptional range could be used to build anything from spacecraft to sneaker shock absorbers, notes Yury Gogotsi, a nanotechnologist at Drexel University who wrote a Perspective in Science to accompany the research.

The new material is made of a random network of interconnected single-, double- and triple-walled nanotubes — the researchers say the random connections are analogous to a clump of hair. Each carbon nanotube makes connections with numerous other carbon nanotubes. The researchers think its incredible flexibility stems from the entangled network of connections, which work like springs creating elasticity, and from energy dissipation through the zipping and unzipping of carbon nanotubes at these points of contact.

It's still prohibitively expensive to produce the super-rubber for mass consumption, Gogotsi said. But someday, it could be used to make wrinkle-free fabrics, electricity-harvesting shoes and new spacecraft materials.

[via Discovery News]

Shot with a high-speed camera at various frame rates, the precisely controlled water droplets were launched at the nanotube arrays at different velocities and at different impact angles. The first segment of the video shows a simple 30 microliter droplet of water striking the array at two different speeds. At a slower 1.03 meters per second the droplet bounces off the nanotubes almost completely intact; at increased velocity it breaks into several smaller droplets and scatters in different directions.

But the really interesting segments of the video come later when the researchers start playing with the tilt and the shape of the nanotube array. We don’t want to spoil the climactic ending, but it involves two identical 14 microliter droplets rushing toward each other like star-crossed lovers racing across a field of tiny nanotubes. Who says science lacks romance?

[arXiv]

The batteries were fabricated by materials scientists at Stanford by depositing a thin film of carbon nanotubes followed by another thin film of metal-containing lithium compound on top of the nanotube layer. These thin bilayer films are layered onto both sides of a piece of ordinary paper, which serves as both the structural support of the battery as well as the electrode separator. The lithium serves as electrodes, while the nanotube layers are current collectors.

The result is a working battery just 300 micrometers thick – that’s 300 millionths of a meter – that is flexible, super-thin, and more energy dense than other thin-bodied batteries. It’s also durable; over a 300-cycle recharge test, performance remained satisfactory. It’s also fairly easy to fabricate, making it far more commercially viable than other methods of downsizing battery technology.

Such batteries aren’t ideal for every application, but they could be extremely useful in future incarnations of smart packaging, RFID sensing, and electronic paper products.

[Chemical & Engineering News]

Michael Crommie, a senior scientist in the Materials Sciences Division at Berkeley Lab and a physics professor at the University of California-Berkeley, says this is a completely new effect that has no counterpart in any other condensed matter system.

Since scientists began studying magnetic fields more than 100 years ago, no one has been able to sustain big magnetic fields for very long. The record is 85 tesla -- a measurement of electromagnetism named for Nikola Tesla -- and it only lasted a few thousandths of a second. Make it stronger than that, and the magnets blow themselves apart.

But in Crommie's study, electrons inside carbon atoms behaved as if they were subjected to 300 tesla. It has to do with the way graphene is constructed, which leaves one out of every four valence electrons free to hop around. The other three electrons form tight hexagonal chains. When graphene sheets are strained -- for instance, when they're rolled up into carbon nanotubes or stretched into nanobubbles -- the bond lengths between atoms change, and electrons hop differently.

The effect is so strong that it works at room temperature. Berkeley Lab's news site has a more detailed description here.

The finding could lead to better electronic and magnetic devices, Crommie says. Controlling where electrons exist and how they move is an essential feature of all electronic devices, he notes.

"New types of control allow us to create new devices, and so our demonstration of strain engineering in graphene provides an entirely new way for mechanically controlling electronic structure in graphene," he says.

[Lawrence Berkeley National Laboratory]