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

Tuesday, 10 December 2019

The newly discovered Plastic hardens 1800 times on Heating

The soft, transparent gel at 25 ° C does not support weight (top), but quickly becomes rigid and opaque when heated to 60 ° C, becoming strong enough to support weight (bottom).

Heat hardening plastic

Researchers at Hokkaido University in Japan have developed a hydrogel that does the opposite of what polymer-based materials - such as plastic bottles - usually do: the material hardens when heated and softens when cooled.

The new material, which hardens 1,800 times when exposed to heat, could protect motorcyclists and race car drivers during accidents.

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Takayuki Nonoyama and his colleagues were inspired by how proteins remain stable within living things that survive in extreme heat environments, such as hot springs. Normally, heat "denatures" proteins, altering their structure and breaking their bonds. But proteins in thermophiles remain stable with heat, thanks to specially reinforced electrostatic interactions such as ionic bonds.

They mimicked this behavior by using a low-cost, non-toxic polyacrylic gel.

Phases of Polymers

The poly [acrylic acid] polyelectrolyte gel (PAAc) was immersed in an aqueous calcium acetate solution. PAAc itself behaves like any other polymer-based material, softening when heated. But when calcium acetate is added, the molecules of materials interact in a similar way to thermophilic proteins, causing PAAc to behave very differently.

As the temperature rises, the originally uniform gel separates into a dense polymer "phase" and a sparse polymer "phase." When it reaches a critical temperature of around 60 ° C, the dense phase undergoes severe dehydration, which strengthens ionic bonds and hydrophobic interactions between polymer molecules.

This causes the material to change rapidly from a soft, transparent hydrogel to a rigid, opaque plastic - 1,800 times stiffer, 80 times stronger and 20 times stronger than the original hydrogel.

Simply lowering the temperature causes the behavior to reverse, which opens up numerous possibilities for application.

Molecular structures and the mechanisms behind instant hydrogel thermal hardening.

Temperature sensitive intelligent materials

The team demonstrated one of the possible applications by combining the material with a fiberglass. The resulting composite fabric is soft at room temperature, but when it was rotated on an asphalt surface for five seconds at a speed of 80 km / hour, the heat generated by the friction was sufficient to harden the material with only minor abrasions. forming on the contact surface.

"Clothing made of similar fabric can be used to protect people during traffic accidents or sports, for example. Our material can also be used as a heat-absorbing window covering to keep indoors cooler," said Nonoyama.

"This polymeric gel can easily be made from versatile, inexpensive, non-toxic raw materials commonly found in everyday life. Specifically, polyacrylic acids are used in disposable diapers and calcium acetates are used in food additives. Our study contributes to basic research on new temperature sensitive polymers and applied research on intelligent temperature sensitive materials, "added Professor Jian Ping Gong.


Instant Thermal Switching from Soft Hydrogel to Rigid Plastics Inspired by Thermophile Proteins

Takayuki Nonoyama  Yong Woo Lee  Kumi Ota  Keigo Fujioka  Wei Hong  Jian Ping Gong

Advanced Materials 2019

A new type of artificial skin capable of self-regeneration

Research focused on the development of artificial skins could benefit both people with bioprostheses and robotics. In recent years, significant progress has been made in this direction, but none of the prototypes created to date have combined all the properties of human skin. This is today done. Recently, a team of Australian bioengineers has developed a new type of hydrogel that acts as an artificial skin and combines the strength, durability, flexibility and self-regeneration of human skin.

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This new hydrogel could be used as skin, tendon or muscle. " Thanks to the special chemistry we have incorporated into the hydrogel, it can repair itself after being damaged, as can human skin. Hydrogels are usually fragile, but our material is so strong that it could easily lift heavy objects. It can also change shape as human muscles do, "says chemist Luke Connal of the Australian National University.

The creation of a hydrogel that changes shape and has multiple functions has proven to be a permanent challenge for scientists, even with the natural inspiration of jellyfish, sea cucumbers and fly-flyers. While some hydrogels can withstand mechanical stresses, others have self-healing properties, and some have the ability to memorize shapes or change color.

An extremely reactive artificial skin

As far as UNA researchers know, no one else has been able to incorporate all these functions into one universal gel. By submitting their material to multiple tests, the authors claim to have created the first dynamic hydrogel that is solid, resistant to mechanical stresses, wear-resistant, self-healing and able to change shape and retain memory. The technical details have been published in the journal Advanced Materials.

Structure and preparation of the hydrogel. Credits: Zhen Jiang et al. 2019

Using this material, the researchers made extremely thin films of "flesh" without any breakage. When these films were heated or cooled, they then changed shape, bending one way or the other before returning to their original state with the right temperature.

Mechanical properties of the hydrogel: elasticity, strength, hardness. Credits: Zhen Jiang et al. 2019

Unlike many other hydrogels, which can sometimes take 10 minutes or more to change shape, this gel only takes 10 seconds to bend. Here, the key would be the dynamic hydrogen bonds of the gel and the imine (carbon-nitrogen) dynamic bonds, which work together to form "unprecedented properties".

Towards a more "human" robotics

Dynamic bonds have a high response to stimuli, making them perfect for environmental adaptation and self-healing, and imine bonds in particular have fast reaction kinetics that can allow rapid self-healing. . In addition, the authors claim that these materials can be easily prepared using simple chemistry, and if other polymers are added to the molecular mixture, perhaps even more functions can be achieved.

If the temperature is somehow used as a control, the authors think that this gel could one day be used as an artificial muscle. " In many sci-fi films, we see the most challenging work done by humanoid robots. Our research has taken an important step toward achieving this, "said materials engineer Zhen Jiang. In the meantime, the team hopes to turn their hydrogel into a printable 3D ink.


Tough, Self‐Healing Hydrogels Capable of Ultrafast Shape Changing

Zhen Jiang Broden Diggle India C. G. Shackleford Luke A. Connal

Volume31, Issue 48

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