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Showing posts with label Materials. Show all posts
Showing posts with label Materials. Show all posts

Monday, 4 November 2019

Recycle heat to electricity with ultracentrifed liquids

 By circulating liquids in charged nanoscale channels, it is possible to convert heat into electricity as efficiently as the best thermoelectric materials.

When subjected to a temperature difference, a nanofluidic channel can generate electricity , with a performance comparable to that of the best thermoelectric solids.
© ILM (CNRS / University of Lyon 1)

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The materials solid thermoelectric can convert a temperature difference into electric energy . They thus constitute an important energy resource for the years to come. However, the best performing materials are rare, expensive and often toxic. Physicists of theInstitut light material in Lyon (. CNRS / University Lyon 1) explored an alternative possibility: using nanofluidic channels confining the water salty. Such systems have received much attention recently because they are able to produce electricity from the osmotic energy of seawater . This "blue energy" comes from the phenomenon of osmosis , that is to say the spontaneous flow of the liquid from the most concentrated to the least concentrated medium. But the application of these devices for recycling in heat electricity lost by many industrial processes in electricity is only beginning to be studied. This lower interest is explained by the standard image of the thermoelectricity of charged liquids, developed in the 1980s, and which predicted performance far below that of thermoelectric materials.

Scientists have tested these models using simulations of the behavior of matter at the atomic level. In this type of simulation, the motion of each atom is explicitly described, which allows to measure independently the influence of the various parameters (interactions with the walls, electrostatic contribution) on the movement of the atoms and therefore of the electric current.. Against all odds, they showed that the performance of nanofluidic systems was a hundred times better than the predictions of standard models, and could be comparable to those of the best thermoelectric solid materials. This work demonstrates the potential of nanofluidic systems, and by understanding their mechanisms, they can serve as a guide for the development of high performance devices, a cost-effective and non-toxic alternative to thermoelectric materials.


Monday, 21 October 2019

For the first time, fractal distributions have been demonstrated in a quantum material

Fractals are mathematical objects whose internal patterns are repeated, forming an invariant structure by scaling. From snowflakes to lightning, fractals are found in many natural phenomena. And recently, MIT researchers have demonstrated a fractal distribution of magnetic domains in a material with particular quantum properties.

MIT physicists provided the first known example of a fractal arrangement in a quantum material. The patterns have been observed in an unexpected distribution of magnetic units called "domains", which develop in a compound called nickel-neodymium oxide - a rare earth metal with amazing properties. The study was published in Nature Communications .

A better understanding of these areas and their structures could potentially lead to new ways of storing and protecting digital information. As the physicist Riccardo Comin explains, " the material is not magnetic at all temperatures ".

Geometric distribution of magnetic domains in nickel-neodymium oxide 

The atoms of nickel oxide and neodymium form minute clusters of magnetically oriented particles called domains. The domains come in different sizes and arrangements, depending on the quantum interactions between the electron s and their atoms under certain conditions. But the question was how they emerged in nickel-neodymium oxide, given its nature as a driver.

" We wanted to see how these areas appear and develop once the magnetic phase is reached when cooling the material, " says Comin. Researchers have in the past studied the unique magnetic properties of the material through X-rays. While this showed how the material was distributing its electrons at different temperatures, mapping the size and distribution of its domains under such conditions required more focused approach.

Experimental protocol used by researchers to analyze magnetic domain structures. Credits: Jiarui Li et al. 2019
" We have therefore adopted a special solution that focuses the X-ray beam, so that we can map, point by point, the arrangement of the magnetic domains in this material, " says Comin.

Fresnel lenses are stacked layers of transparent material with ridges, which redirect electromagnetic radiation. The lenses that Comin and his team developed were only 150 microns wide. The end result was an X-ray beam small enough to detect the fine scale of the magnetic domains through a thin neodymium nickel oxide film developed in the laboratory.

Fractal distribution of magnetic domains

Most of these areas were tiny. Scattered among them were bigger ones. But once the data was analyzed and a map was modeled, the distribution of larger domains among the many much smaller domains was strangely similar, regardless of the scale used.

Fractal distribution of magnetic domains in nickel-neodymium oxide. Credits: Jiarui Li et al. 2019

 The schema of the models was difficult to decipher at first, but after analyzing the statistics of the domain distribution, we realized that it had fractal behavior. It was completely unexpected, pure chance, "says Comin. Materials that can be used as both conductors and insulators already play an important role in the world of electronics. Transistors are based on this very principle.

But nickel-neodymium oxide has another property. The same fractal pattern of domains reappears when the temperature drops again, almost as if it had some sort of memory. " Similar to magnetic disks in rotating hard disks, we can consider storing bits of information in these magnetic domains, " concludes Comin.

Monday, 24 June 2019

Researchers found a way to restore sight of blind people using Orgnic Printing

One of the research leaders, Eric Glowacki, measures the electrical response of the neurostimulation devices to pulses of red light Photo credit: Thor Balkhed

A simple retinal prosthesis is being developed in collaboration between Tel Aviv University in Israel and LiU. Fabricated using cheap and widely-available organic pigments used in printing inks and cosmetics, it consists of tiny pixels like a digital camera sensor on a nanometric scale. Researchers hope that it can restore sight to blind people.

Researchers led by Eric Glowacki, principal investigator of the organic nanocrystals subgroup in the Laboratory of Organic Electronics, Linköping University, have developed a tiny, simple photoactive film that converts light impulses into electrical signals. These signals in turn stimulate neurons (nerve cells). The research group has chosen to focus on a particularly pressing application, artificial retinas that may in the future restore sight to blind people. The Swedish team, specializing in nanomaterials and electronic devices, worked together with researchers in Israel, Italy and Austria to optimise the technology.

Experiments in vision restoration were carried out by the group of Yael Hanein at Tel Aviv University in Israel. Yael Hanein’s group is a world-leader in the interface between electronics and the nervous system.

Photoactive material

The retina consists of several thin layers of cells. Light-sensitive neurons in the back of the eye convert incident light to electric signals, while other cells process the nerve impulses and transmit them onwards along the optic nerve to an area of the brain known as the “visual cortex”. An artificial retina may be surgically implanted into the eye if a person’s sight has been lost as a consequence of the light-sensitive cells becoming degraded, thus failing to convert light into electric pulses.

The artificial retina consists of a thin circular film of photoactive material, and is similar to an individual pixel in a digital camera sensor. Each pixel is truly microscopic – it is about 100 times thinner than a single cell and has a diameter smaller than the diameter of a human hair. It consists of a pigment of semi-conducting nanocrystals. Such pigments are cheap and non-toxic, and are commonly used in commercial cosmetics and tattooing ink.

“We have optimised the photoactive film for near-infrared light, since biological tissues, such as bone, blood and skin, are most transparent at these wavelengths. This raises the possibility of other applications in humans in the future,” says Eric Glowacki.

Microscopic donut

He describes the artificial retina as a microscopic doughnut, with the crystal-containing pigment in the middle and a tiny metal ring around it. It acts without any external connectors, and the nerve cells are activated without a delay.

“The response time must be short if we are to gain control of the stimulation of nerve cells,” says David Rand, postdoctoral researcher at Tel Aviv University. “Here, the nerve cells are activated directly. We have shown that our device can be used to stimulate not only neurons in the brain but also neurons in non-functioning retinas.”


Direct Electrical Neurostimulation with Organic Pigment Photocapacitors.
 David Rand, Marie Jakešová, Gur Lubin, Ieva Vėbraitė, Moshe David-Pur, Vedran Đerek, Tobias Cramer, Niyazi Serdar Sariciftci, Yael Hanein, Eric Daniel Głowacki.
 Advanced Materials, 2018; 1707292
DOI: 10.1002/adma.201707292

Thursday, 20 June 2019

Controlling Thermal Conductivity of Polymers with Light

Under ambient conditions or visible light (left side), the polymer is crystalline and has a high thermal conductivity. Once exposed to ultraviolet (UV) light (right side), the bond becomes a liquid of low thermal conductivity - the crystalline phase appears bright and the liquid phase appears dark. [Image: University of Illinois Materials Research Lab]

Heat control with light

The plastics capable of conducting heat are a recent class of new materials used in electronics and promise lighter cars .

The newest member of this family is a plastic that has its thermal conductivity controlled by light: Light can function as an optical switch, turning on and off the plastic's ability to conduct heat.

This means that this polymer will allow to route the heat on demand, taking it to where it is needed or removing it from where it is harmful.

"As far as we know, this is the first observation of a light-reversible reversible crystal-liquid transition in any polymer material." The particularly notable finding in this study is the rapid and reversible three-fold change in thermal conductivity associated with phase transition, said Jungwoo Shin of the University of Illinois, USA.

This possibility of optical control of the thermophysical properties of the polymer is due to the photoresponsive effect of the azobenzene molecule , which can be optically energized by visible light or by ultraviolet light.

"By synthesizing it with visible and visible UV light, we can change the shape of the azobenzene group by modulating the bond strength between the chains and producing a reversible transition between crystal and liquid," he said. Jaeuk Sung, a member of the team.

The next step will be to study the resilience of the polymer under various operating conditions, to define its possible uses.


 Light-triggered thermal conductivity switching in azobenzene polymers
Jungwoo Shin, Sung Jaeuk, Minjee Kang, Xu Xie, Byeongdu Lee, Kyung Min Lee, Timothy J. White, Cecilia Leal, Nancy R. Sottos, Paul V. Braun, David G Cahill
 Proceedings of the National Academy of Sciences
 DOI: 10.1073 / pnas.1817082116

Bulletproof wood now also fire resistant

The flame retardant effect is generated by the formation of a layer of charcoal on the surface of the wood subjected to fire. [Image: Wentao Gan et al. - 10.1002 / adfm.201807444]

Anti-fire wood

The creators of bulletproof wood have taken yet another surprising step to make wood a competitor to the height of synthetic materials.

Wentao Gan and his colleagues at the University of Maryland, USA, have concluded that their superdurated wood is extremely fire-resistant.

They have discovered how to use a chemical compound to soften the wood, allowing it to be compressed, removing the spaces between the cell walls.

When subjected to fire, this compressed wood forms a protective layer of coal on its surface, which prevents fire from spreading and preserves the internal structural integrity of the wood.

In other words, in addition to not burning readily, the wood structure does not collapse, as occurs with ordinary wood constructions.

The effects of the treatment are dramatic in terms of resistance to burning. [Image: Wentao Gan et al. - 10.1002 / adfm.201807444]

Fire-resistant wood

There are already techniques to make the wood more resistant to fire by means of chemical treatments. But these techniques are expensive and far from being environmentally friendly, as they involve injection into the wood of halogenated flame retardants or coatings of inorganic nanoparticles. Also, the wood does not get strong enough.

The treatment to make fire-resistant wood is virtually the same as used to make the superdurated wood presented by the team last year.

In tests, the ignition timing of the wood doubled, while its heat release was reduced by more than a third.


 Dense, Self-Formed Char Layer Enables a Fire-Retardant Wood Structural Material

Wentao Gan, Chaoji Chen, Zhengyang Wang, Jianwei Song, Yudi Kuang, Shuaiming He, Ruiyu Mi, Peter B. Sunderland, Liangbing Hu
 Advanced Functional Materials 
 DOI: 10.1002 / adfm.201807444

Tuesday, 18 June 2019

Metamaterial revolutionizes magnetic resonance imaging (MRI) and medical imaging

Prototype of the cylinders that form the metamaterial. [Image: Duan et al. - 10.1038 / s42005-019-0135-7]

Metamaterial for exams

The metamaterials , which began as a mathematical curiosity and soon proved even more curious, by enabling the creation of invisibility cloaks , are already ready to improve medical examinations.

A team at Boston University in the United States created a magnetic metamaterial in the form of a small cylinder that proved capable of strongly amplifying the signals from MRI machines.

The result is a much sharper examination done in half the time of the current examinations and still allowing to use a much lower magnetic field, possibly paving the way for the production of lower cost and lower cost equipment.

Magnetic Metamaterial

The magnetic metamaterial consists of a series of units called helical resonators, structures three centimeters high created from plastic printed in 3D and copper coils.

The small devices alone do not impress. However, when placed together, the helical resonators form a flexible matrix, malleable enough to cover the patella, abdomen, head, or any part of the body that needs imaging.

When the array is placed close to the body, the resonators interact with the machine's magnetic field, increasing the signal-to-noise ratio of the MRI, "increasing the volume of the image," as the researchers say.

"The 'magic' part is the design and the idea," said researcher Guangwu Zhang. "Many people are surprised by its simplicity.

Comparison of the MRI scans of 1.5 T with and without the magnetic metamaterial. [Image: Duan et al. - 10.1038 / s42005-019-0135-7]

Next generation magnetic resonance imaging

To test the magnetic set, the team examined chicken legs, tomatoes and grapes using a 1.5 Tesla machine. The magnetic metamaterial produced a 4.2-fold increase in the signal-to-noise ratio, a radical improvement, which means that lower magnetic fields could be used to take clearer images than is currently possible.

Researchers now hope to partner with the industry so their magnetic metamaterial can be adapted to real-world clinical applications.


Boosting magnetic resonance imaging signal-to-noise ratio using magnetic metamaterials
Guangwu Duan, Xiaoguang Zhao, Stephan William Anderson, Xin Zhang
Communications Physics
Vol. 2, Article number: 35
DOI: 10.1038 / s42005-019-0135-7

Wednesday, 12 June 2019

New Developed Fiber is as Flexible as Elastic But Tough as Steel

Metal-rubber composite

Researchers have developed a fiber that combines the elasticity of rubber with the strength of a metal.

The resulting composite is a sturdier material that can be incorporated into lightweight robotics, packaging materials, next generation textiles and even in biomedical applications.

"A good way to explain the material is to think of elastics and metal wires.An elastic can stretch a lot, but it does not take much force to stretch it.A metal wire requires a lot of force to be stretched, but it does not take much "Our fibers have the best of these two worlds," explained Professor Michael Dickey, of the State University of North Carolina, USA.

The fibers consist of a metal core of gallium encased by an elastic polymer coating.

When placed under stress, the fiber has the strength of the metal core. But when the force is too much and the metal breaks, the fiber does not break - the polymer coating absorbs the tension between the broken metal parts and transfers the voltage back to the still intact parts of the metal core.

"Every time the metal core breaks, it dissipates energy, allowing the fiber to continue to absorb energy as it stretches," explained Dickey. "Instead of splitting in two when stretched, it can stretch up to seven times the original length before breaking, which happens while many additional breaks in the yarn are generated along the way."

Tenacity of the skin

The fiber response is similar to the way human connective tissue is maintained when a bone breaks.

"There is a lot of interest in engineering materials to mimic the tenacity of the skin - and we have developed a fiber that has overcome the tenacity of the skin and is still elastic like the skin," said Dickey.

The fibers can be reused by melting the metal cores again - gallium fuses at a mere 30 ° C, which means that the polymer is not affected.

"This is just a proof of concept, but it has a lot of potential. We are interested to see how these fibers could be used in light robotics or when woven into fabrics for various applications," said Dickey. 

Toughening stretchable fibers via serial metal fracturing Christopher B. Cooper, Ishan D. Joshipura, Dishit P. Parekh, Justin Norkett, Russell Mailen, Victoria M. Miller, Jan Genzer, Michael D. Dickey Science Advances Vol .: 5, no. 2, eaat4600 DOI: 10.1126 / sciadv.aat4600