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

Thursday, 13 February 2020

As seen in Movies, Holograms can be used as a communication tool

For the time being the team has only managed to transmit letters and small messages, but the future is promising, as seen in this art. [Image: Nanoscale Horizons]


Those who  have watched the film Black Panther saw people from the Wakanda Kingdom communicating through holograms. And that specific scene of fiction can become a reality sooner than you might imagine, allowing you to exchange different information with people from different locations.

This possibility is being made possible by the creation of "meta-holograms", which are modified versions of the same holograms used to prevent counterfeiting, in notes and credit cards.

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The difference is that the meta-holographic structures are capable of showing one image when the incident light is in one direction, and another different image when the light is coming from the other direction.

In addition, the meta-holograms created now by a team at Pohang University in South Korea are thin and light, making them easier to apply in practice - they fall into the field of metamaterials , the same ones that manipulate light to create the mantles of invisibility.



Televisions and beam projectors can only transmit intensity of lights but holographic techniques can save light intensity and its phase information to play movies in three-dimensional spaces. At this time, if metamaterials are used, a user can change nano structures, size, and shapes as desired and can control light intensity and phase at the same time. Meta-hologram has pixel sizes as small as 300 to 400 nanometers but can display very high resolution of holographic images with larger field of view compared to existing hologram projector such as spatial light modulator.

Device illustration (left) and real images transmitted to one side and the other (right) - consider that the meta-surface is in the center of the black square.

To get ahead, the team used two different types of meta-surfaces - essentially flat metamaterials. The first meta-surface was designed to have phase information when the incident light is in the "forward" direction, while the other operates when the light is in the "back" direction.

As a result, different images are displayed in real time, depending on the direction of the light - or, in other words, transmitting different information to different locations.

In addition, the team applied dual magnetic resonances and antiferromagnetic resonances, which are phenomena occurring in silicon nanopillars, to nanostructure design to overcome low efficiency of the conventional meta-hologram. This newly made meta-hologram demonstrated diffraction efficiency higher than 60% (over 70% in simulation) and high-quality and clear images were observed.

Furthermore, the new meta-hologram uses silicon and it can be easily produced by following through the conventional semiconductor manufacturing process.



Junsuk Rho who is leading research on metamaterials said, 'Microscopic, ultrathin, ultralightweight flat optical devices based on a metasurface is an impressive technique with great potentials as it can not only perform the functions of the conventional optical devices but also demonstrate multiple functions depending on how its metasurface is designed. Especially, we developed a meta-hologram optical device that operated in forward and backward directions and it could transmit various visual information to multiple users from different locations simultaneously. We anticipate that this new development can be employed in multiple applications such as holograms for performances, entertainment, exhibitions, automobiles and more."


Bibliography:

Article: Engineering spin and antiferromagnetic resonances to perform an efficient direction-multiplexed visible meta-hologram

Authors: Muhammad Afnan Ansari, Inki Kim, Ivan D. Rukhlenko, Muhammad Zubair, Selcuk Yerci, Tauseef Tauqeer, Muhammad Qasim Mehmood, Junsuk Rho

Magazine : Nanoscale Horizons

DOI: 10.1039 / D0NH90006K

Thursday, 6 February 2020

New type of symmetry discovered, hidden in artificial materials

Autodual symmetries emerge at critical points, causing two completely different materials to conduct sound in the same way.


It is not every day that you discover a new type of symmetry in nature.
Even less discover symmetries hidden in man-made artificial materials.
And the discovery has numerous immediate practical applications.

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A trio of researchers from the University of Chicago, USA, discovered a symmetry hidden inside the solids when using sound waves to study the interior of the materials. They used Lego blocks to build regular structures and assess how they react to sound.

What they found is that completely different structures can produce the same sound - something like hitting a green watermelon and a ripe watermelon and hearing the same sound.



"What excited us was the fact that we cannot explain our findings using existing concepts, such as spatial symmetries," said Professor Vincenzo Vitelli, recalling that physicists have used these concepts for decades to describe and predict the properties of an object with based on their spatial symmetries.

The new explanation that has emerged is what the researchers call "duality", a hidden symmetry associating apparently unrelated parts of the solid.

"We observed that pairs of distinct configurations along the mechanism have the same vibrational spectrum and related elastic modules. We demonstrated that these intriguing properties arise from a duality between pairs of configurations on both sides of a critical mechanical point," wrote the team. In other words, it is a self-duality, which emerges when a duality becomes recurrent in a periodic material.

In the past few years, there has been an explosion of interest in a field called metamaterials. These are artificial structures engineered to have characteristics not normally expected in nature. For example, much thought has gone into realizing an "invisibility cloak" using composite materials that bend incoming light around them by virtue of their internal geometry.



Fruchart and Vitelli imagined using this approach to take a particle such as a phonon—essentially a particle of heat—and give it properties that it doesn't usually have.

The discovery of this duality promises to have a great impact on the design of metamaterials , allowing to design artificial materials that have specific properties.

Most metamaterials have been designed to handle light, but this new symmetry paves the way for the design of artificial materials that manipulate sound - phonons, which are "particles of heat", rather than photons, particles of light.

Electrons have a property called "spin", which is used as the basis for some of the latest high-tech electronics. Phonons, in turn, do not have an intrinsic spin, but if it is possible to shape the structure of materials, it is possible to give phonons a "pseudo-spin". Vitelli and his colleagues called this concept "mechanical spintronics".

This would allow us to use these materials in phononic devices - similar to electronics, but with different skills, enabling phononics, or "heat electronics".



"Our approach also applies to other waves, not just phonons - for example, waves of light and matter," said researcher Michel Fruchart.


Bibliography:

Article: Dualities and non-Abelian mechanics

Authors: Michel Fruchart, Yujie Zhou, Vincenzo Vitelli

Magazine: Nature

Vol .: 577, pages 636-640

DOI: 10.1038 / s41586-020-1932-6

Monday, 27 January 2020

Scientists create Crystal inside a crystal to improve screens and more

The beautiful patterns created by blue liquid phase crystals have a number of technological applications.

Liquid crystals have enabled new technologies, such as LCD screens, thanks to their ability to reflect certain wavelengths of light, or colors, and to be very easy to manipulate.

Researchers have now developed an innovative way to sculpt a crystal inside a liquid crystal.
Because these crystals within crystals can reflect light at certain wavelengths that others cannot, they can be used to improve screen and monitor technologies.

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They can also be manipulated with temperature, electrical voltage or chemicals, which makes them valuable for detection applications. Temperature changes, for example, would result in color changes. And since these changes require only small temperature variations or small voltages, the devices would consume very little energy.

Creating an interface between crystals

The molecular orientation of liquid crystals makes them useful in key functions of various display technologies. They can also form "blue phase crystals", in which the molecules are arranged in highly regular patterns, which reflect visible light.

To design a blue phase crystal interface, Xiao Li and his colleagues at the University of Chicago, USA, developed a method that is based on chemically patterned surfaces, on which liquid crystals are deposited, thus providing a means of manipulating their orientation molecular. This orientation is then amplified by the liquid crystal itself, allowing a specific blue phase crystal to be carved into another blue phase crystal.



The process, the result of theoretical predictions and experimentation to arrive at the right design, allowed the creation of specific crystal forms within the liquid crystals - something unprecedented.

Not only that: The newly sculpted crystal can be manipulated with temperature and electricity to change from a blue phase to another type of blue phase, thus changing color.

"This means that the material can change its optical characteristics very precisely," said Professor Juan de Pablo, from the Argonne National Laboratory. "We now have material that can respond to external stimuli and reflect light at specific wavelengths, for which we had no good alternatives before."

This ability to manipulate crystals on such a small scale also makes it possible to use them as models to manufacture perfectly uniform structures at the nanoscale.

Details of the manufacturing process and the interfaces inside the crystal.

Blue phase crystals

Blue phase crystals have the properties of liquids and crystals, which means that they can flow and are flexible, while having highly regular characteristics that transmit or reflect visible light.

They also have better optical properties and a faster response time than traditional liquid crystals, making them good candidates for optical technologies.

In addition, the projections responsible for reflecting light in the blue phase crystals are separated by relatively large distances compared to traditional crystals, such as quartz. The larger size of these projections facilitates the engineering of the interfaces between them, a process notoriously difficult in traditional crystalline materials.

These interfaces are important because they provide ideal locations for chemical reactions and mechanical transformations, and because they can make it difficult to transport sound, energy or light.





Bibliography:

Article: Sculpted grain boundaries in soft crystals

Authors: Xiao Li, José A. Martínez-González, Orlando Guzmán, Xuedan Ma, Kangho Park, Chun Zhou, Yu Kambe, Hyeong Min Jin, James A. Dolan, Paul F. Nealey , Juan J. de Pablo

Magazine: Science Advances

Vol .: 5, no. 11, eaax9112

DOI: 10.1126 / sciadv.aax9112

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.




Bibliography:

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

https://doi.org/10.1002/adma.201905878

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.




Bibliography:

Tough, Self‐Healing Hydrogels Capable of Ultrafast Shape Changing

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

Volume31, Issue 48

https://doi.org/10.1002/adma.201904956

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