Mimetizând structura pielii umane, cercetătorii au folosit o tehnică strat-cu-strat pentru a forma un strat subțire dinamic, conținând alcool polivinilic și acid tanic. Stratul exterior dur conținea acești compuși plus un strat de oxid de grafen. Când este fabricat la o anumită grosime, materialul sa vindecat cu succes atunci când a fost tăiat și, de asemenea, ar putea ucide bacteriile.
Materialul ar putea într-o bună zi să servească ca o piele electronică sau chiar ca o acoperire rezistentă la zgârieturi pe clădiri sau pe telefoane.
Posted: Jan 31, 2018
Skin-inspired graphene oxide based coating that’s as hard as teeth and can heal itself
(Nanowerk News) Self-healing smart coatings could someday make scratches on cell phones a thing of the past. But researchers often have to compromise between strength and the ability to self-repair when developing these materials.
The smart coating market is a booming industry and is only expected to grow in upcoming years. The most common smart coatings that can heal themselves are based on soft polymers that can wear out quickly. But hard coatings can be too rigid to come back together to fix a tear or scratch.
In previous research, Ming Yang and colleagues produced a stiffer, more healable coating, but its performance still needs to be optimized. In the current paper, the researchers developed a different way to make a soft, yet hard, self-healing material.
Mimicking the structure of human skin, the researchers used a layer-by-layer technique to form a soft, dynamic under layer containing polyvinyl alcohol and tannic acid. The hard outer layer contained these compounds plus a layer of graphene oxide. When fabricated at a certain thickness, the material successfully healed itself when cut, and it also could kill bacteria.
The material could someday serve as an electronic skin or even as a scratch-proof coating on buildings or phones.
O echipa de cercetatori de la Universitatea Hokkaido si Universitatea Kansai a dezvoltat roboti moleculare asistate de ADN, care se rotesc in mod autonom ca raspuns la semnalele chimice si fizice, deschizand calea pentru dezvoltarea viitoarelor nano-masini.
Cel mai mic „robot roșu” din lume măsoară 25 nanometri în diametru și 5 micrometri în lungime și prezintă un comportament roșu asemănător unor organisme motile cum ar fi peștii, furnicile și păsările.era de așteptat ca un astfel de sistem să contribuie la dezvoltarea mușchilor artificiali și a diagnosticelor genetice, precum și la construirea de nanomateriale în viitor „, a comentat Kakugo.
Posted: Jan 31, 2018
Letting molecular robots swarm like birds
(Nanowerk News) A team of researchers from Hokkaido University and Kansai University has developed DNA-assisted molecular robots that autonomously swarm in response to chemical and physical signals, paving the way for developing future nano-machines.
The world’s smallest „swarm robot” measures 25 nanometers in diameter and 5 micrometers in length, and exhibits swarming behavior resembling motile organisms such as fish, ants and birds.
„Swarm robots are one of the most elusive subjects in robotics,” says Akira Kakugo of the research team at Hokkaido University. „Fish schools, ant colonies and bird flocks show fascinating features that cannot be achieved by individuals acting alone. These include the formation of complex structures, distinct divisions of labor, robustness and flexibility, all of which emerge through local interactions among the individuals without the presence of a leader.” Inspired by these characteristics, researchers have been working to develop micro-scale swarm robots.
In the present study (Nature Communications, „DNA-assisted swarm control in a biomolecular motor system”), Kakugo and his collaborators have built a molecular system that is composed of the three essential components of a robot: sensors, information processors and actuators. They used cellular proteins called microtubules and kinesins as the actuator, and DNA as the information processor. Microtubules are filamentous proteins that serve as the railways in the cellular transportation system, while kinesins are motor proteins that run on the railways by consuming chemical energy obtained from hydrolysis of adenosine triphosphate (ATP). The team took a reverse strategy and built a system in which microtubules move randomly on a kinesin coated surface.
A major challenge in swarm robotics is the construction of a large number of individual robots capable of programmable self-assembly. The team addressed this issue by introducing DNA molecules into the system that are known to hybridize when they have a complementary sequence. The chemically synthesized DNA molecules with certain programs in their sequences are conjugated to the microtubules labeled with green or red fluorescence dye.
The team then monitored the motions of the DNA-conjugated microtubules gliding on a kinesin coated surface. Initially, five million microtubules moved without any interactions with each other. They then added single-strand linker DNA (l-DNA), programmed to initiate interactions among the DNA-attached microtubules. Upon introduction of the l-DNA, the microtubules began to assemble and formed swarms of a much larger size than the microtubules. When another single-strand DNA (d-DNA), programmed to dissociate the swarms was added, the microtubule swarms disappeared soon. This demonstrated that swarming of a large number of microtubules can be reversibly regulated by selectively providing the input DNA signal in the system.
Moreover, they added a photosensitive sensor to the system, azobenzene attached to the DNA molecules. They utilized isomerization of the azobenzene that occurs reversibly in response to irradiation of visible or ultraviolet light to switch on or off the interaction between DNA molecules. This enabled the photo-irradiation induced switching between the solitary and swarm state of the microtubules. The team also demonstrated that the swarms of microtubules move with a translational or rotational motion depending on the rigidity of the microtubules.
„This is the first evidence showing that swarming behavior of molecular robots can be programmed by DNA computing. The system acts as a basic computer by executing simple mathematical operations, such as AND or OR operations, leading to various structures and complex motions. It is expected that such a system contributes in developing artificial muscles and gene diagnoses, as well as building nano-machines in the future,” Kakugo commented.
Deși structurile biologice cum ar fi lumina difuză de mătase, alte materiale naturale cu microstructuri similare nu posedă modurile localizate, făcând posibilă localizarea luminii de către Anderson.
„O asemenea diferență face ca mătasea să fie deosebit de interesantă pentru transferul de căldură radiant”, a spus Kim. Mătasele au o emisivitate ridicată pentru lumina infraroșie, ceea ce înseamnă că acestea radiază ușor căldura sau radiația infraroșie, fiind în același timp un bun reflector al luminii solare. Deoarece reflexia puternică de la localizarea lui Anderson este combinată cu emisivitatea ridicată a biomoleculelor în radiația infraroșie, mătasele radiază mai multă căldură decât absorbția, făcându-l ideal pentru pasiv sau „auto-răcire”.
Posted: Jan 31, 2018
Silk fibers could be high-tech ‘natural metamaterials’ (w/video)
(Nanowerk News) New research has demonstrated how the nano-architecture of a silkworm’s fiber causes “Anderson localization of light,” a discovery that could lead to various innovations and a better understanding of light transport and heat transfer.
The discovery also could help create synthetic materials and structures that realize the phenomenon, named after Nobel laureate Philip Anderson, whose theory describes how electrons can be brought to a complete halt in materials due to their “scattering and defects.” The new findings relate not to electrons, but to light transport.
Researchers demonstrated how the nano-architecture of the silk fibers is capable of light “confinement,” a trait that could provide a range of technological applications including innovations that harness light for new types of medical therapies and biosensing. This light-confinement effect in biological and natural tissue, which was unexpected, is made possible by the Anderson localization of light, said Young Kim, an associate professor in Purdue University’s Weldon School of Biomedical Engineering.
New research suggests fibers from a silkworm’s cocoon may represent “natural metamaterials,” a discovery with various technological and scientific implications. (Purdue University image/Young Kim)
The new findings suggest silk fibers may represent “natural metamaterials” and “natural metastructures,” Kim said.
Various research groups have created synthetic “metamaterials” capable of the ultra-efficient control of light. However, metamaterials have limitations because they are often difficult to scale up for commercial production and pose other challenges. Because silk’s nano-architecture is “disordered” instead of meticulously designed periodic structures, the findings suggest a strategy to produce metamaterials that are less expensive to fabricate and manufacture and easier to scale up for industry.
“This is fascinating because realizing Anderson localization of light is extremely challenging, yet we now know that it can be achieved using irregular, disordered nanostructures to create highly packed nanomaterials for strong light scattering as a silkworm produces a silk fiber and spins a cocoon shell in nature,” Kim said.
“Our findings could open up new possibilities for metamaterials and metastructures,” said Kim, who is leading research to better understand the underlying reasons for silk’s white, silvery and lustrous reflection. “I know this is an oxymoron, but we are saying silk fibers represent ‘natural metamaterials’ and ‘natural metastructures.’”
The silk fibers are 10-20 microns in diameter and contain thousands of tiny nanofibrils, each around 100 nanometers wide. For perspective, a human hair is roughly 100 microns in diameter.
A silk fiber has numerous “scattering centers” inside. Anderson localization arises from this light scattering due to disorder in the nanostructure.
“Silk has many nanofibrils, which individually scatter light,” Kim said.
New research has demonstrated how the nano-architecture of a silkworm’s fiber causes „Anderson localization of light,” a discovery that could lead to various innovations and a better understanding of light transport and heat transfer.
For the Anderson localization to occur, there must be both scattering and interference between scattered light waves. Densely packed irregular nanostructures cause light waves to interfere with each other, sometimes in destructive and sometimes in constructive ways. If constructive, the light is intensified.
“If waves are constructively interfering, this forms a very high energy inside the disordered media,” Choi said.
The small size and roughly parallel arrangement of the nanofibrils are conducive to the effect. The scattering power is maximized when there are many scattering centers and when their size is comparable to the wavelength of the light, both criteria found in the silk fibers.
Whereas commercial optical fibers must be specially engineered with a reflective coating, or cladding, to allow for the confinement of light, the silk fibers are able to achieve the feat naturally due to Anderson localization of light. The Anderson localization creates “modes” that make confinement of light possible without carefully engineered periodic structures. Instead, the same confinement is possible with disordered, more random designs.
“We found that most transmission of light disappears in most of the silk surface. However, counterintuitively, in a small area we found that the energy is confined, and this confined energy is transmitted through localized modes,” Kim said. “The localized mode is a unique pathway for energy flow.”
Although biological structures such as silk diffuse light, other natural materials with similar microstructures do not possess the localized, modes making Anderson localization of light possible.
“Such a difference makes silk particularly interesting for radiative heat transfer.” Kim said. The silk has a high emissivity for infrared light, meaning it readily radiates heat, or infrared radiation, while at the same time being a good reflector of solar light. Because the strong reflectivity from Anderson localization is combined with the high emissivity of the biomolecules in infrared radiation, silk radiates more heat than it absorbs, making it ideal for passive, or “self-cooling.”
“You may have heard that silk underwear can keep you cooler in summertime and warmer in winter,” Kim said. “We have learned the basic mechanism behind this observation.”
The work is led by researchers in Purdue’s Weldon School of Biomedical Engineering; the Department of Agricultural Biology of the National Institute of Agricultural Sciences in South Korea; and the Materials and Manufacturing Directorate of the U.S. Air Force Research Laboratory. A complete list of co-authors is available in the abstract.
“Our findings could open up largely unexplored opportunities for engineering, energy, and biomedical areas,” Kim said. “However, while direct applications could be possible, we really want to learn from silk to help develop material synthesis and design processes in the future.”
a studiat perovskitul de halogenuri de plumb cu trei compoziții diferite, inclusiv clorul, bromul și iodul. Nanocristalele fabricate din aceste compuși și aliajele lor pot fi reglate pentru a emite lumină la lungimi de undă care acoperă întreaga gamă vizibilă, păstrând în același timp emisia rapidă de lumină care le conferă performanțe superioare.
Posted: Jan 31, 2018
Materials research team lights the way for more efficient LEDs
(Nanowerk News) Researchers at the U.S. Naval Research Laboratory (NRL) Center for Computational Materials Science, working with an international team of physicists, have revealed that nanocrystals made of cesium lead halide perovskites (CsPbX3), is the first discovered material which the ground exciton state is „bright,” making it an attractive candidate for more efficient solid-state lasers and light emitting diodes (LEDs) (Nature, „Bright triplet excitons in caesium lead halide perovskites”).
„The discovery of such material, and understanding of the nature of the existence of the ground bright exciton, open the way for the discovery of other semiconductor structures with bright ground excitons,” said Dr. Alexander Efros, research physicist, NRL. „An optically active bright exciton in this material emits light much faster than in conventional light emitting materials and enables larger power, lower energy use, and faster switching for communication and sensors.”
The work, which was partially sponsored by the Office of Naval Research through a program managed by Dr. Chagaan Baatar, studied lead halide perovskites with three different compositions, including chlorine, bromine, and iodine. Nanocrystals made of these compounds and their alloys can be tuned to emit light at wavelengths that span the entire visible range, while retaining the fast light emission that gives them their superior performance.
Pictured standing (l-r) are NRL researchers Dr. Alex Efros and Dr. Noam Bernstein; sitting (l-r) are Dr. John Michopoulos and Dr. John Lyons. (Image: U.S. Naval Research Laboratory)
Semiconductors emit light when bound pairs of electrons and holes, known as excitons, recombine in a process called radiative decay.
„In all known semiconductors and semiconductor nanostructures, the lowest energy state for a bound electron-hole pair is a ‘dark’ state,” said Efros. „This means the material emits light slowly and weakly.”
Because in perovskite nanocrystals the lowest energy exciton is bright, the time it takes for the electron and hole to recombine and emit light, known as their radiative lifetime, is 20 times faster than conventional materials at room temperature and 1000 times faster at cryogenic temperatures.
It is known, that quantum-dot based LEDs, or QLEDs, can suffer from „droop,” or reduced efficiency, at high pumping intensity due to processes that dissipate the energy of excitons before they have time to emit light. The decreased radiative lifetime should make it possible for LEDs based on these perovskites to use all of the energy input to create light before it is dissipated through slower processes.
„The increased rate of light emission of these materials holds great promise for various technological applications that rely on LEDs and lasers,” Efros said. „In principle, the 20 times shorter lifetime could therefore lead to 20 times more intense LEDs and lasers.” The power of a laser depends on the gain of the material it is made of, and this gain is proportional to the radiative emission rate.
Communication in free space using visible light, which makes it possible to transmit information in tight beams for long distances without fiber optic or copper cables, would also benefit from the increased light emission rates. „The maximum bandwidth of the communication system is limited by the rate at which the LEDs can turn on and off, and the shorter radiative lifetime translates directly into faster switching and therefore a higher data transmission rate,” says Efros.
Source: By Daniel Parry, Naval Research Laboratory
au creat o sursă de energie personalizabilă, care poate fi tăiată, pliată sau întinsă fără a-și pierde funcția;cum au creat sursă de alimentare portabilă, un supercapacitor, care funcționează ca o baterie rapidă de încărcare și poate fi reîncărcată de mai multe ori.Supercapacitorul editabil este fabricat din material compozit din materiale compozite cu dioxid de mangan întărit. În timp ce dioxidul de mangan este un material obișnuit pentru supercapacitorii, structura nanofire superioară, întărită cu o rețea de nanotuburi de carbon și fibre de nanoceluloză, permite ca electrozii să reziste tulpinilor asociate în timpul procesului de personalizare.
Posted: Jan 30, 2018
A customizable, fabric-like power source for wearable electronics
(Nanowerk News) Scientists at Nanyang Technological University, Singapore (NTU Singapore) have created a customizable, fabric-like power source that can be cut, folded or stretched without losing its function.
A new power source developed by NTU Singapore scientists which can be customised into any shape, such as a Chinese character in this example. (Image: NTU)
Crucially, they have made their supercapacitor customizable or “editable”, meaning its structure and shape can be changed after it is manufactured, while retaining its function as a power source. Existing stretchable supercapacitors are made into predetermined designs and structures, but the new invention can be stretched multi-directionally, and is less likely to be mismatched when it is joined up to other electrical components.
The new supercapacitor, when edited into a honeycomb-like structure, has the ability to store an electrical charge four times higher than most existing stretchable supercapacitors. In addition, when stretched to four times its original length, it maintains nearly 98 per cent of the initial ability to store electrical energy, even after 10,000 stretch-and-release cycles.
Experiments done by Prof Chen and his team also showed that when the editable supercapacitor was paired with a sensor and placed on the human elbow, it performed better than existing stretchable supercapacitors. The editable supercapacitor was able to provide a stable stream of signals even when the arm was swinging, which are then transmitted wirelessly to external devices, such as one that captures a patient’s heart rate.
A black intricately designed supercapacitor powering a light. Such customisation of the power source opens up new possibilities for wearable electronics in future. (Image: NTU)
The authors believe that the editable supercapacitor could be easily mass-produced as it would rely on existing manufacturing technologies. Production cost will thus be low, estimated at about SGD$0.13 (USD$0.10) to produce 1 cm2 of the material.
The team has filed a patent for the technology.
Professor Chen said, “A reliable and editable supercapacitor is important for development of the wearable electronics industry. It also opens up all sorts of possibilities in the realm of the ‘Internet-of-Things’ when wearable electronics can reliably power themselves and connect and communicate with appliances in the home and other environments.
“My own dream is to one day combine our flexible supercapacitors with wearable sensors for health and sports performance diagnostics. With the ability for wearable electronics to power themselves, you could imagine the day when we create a device that could be used to monitor a marathon runner during a race with great sensitivity, detecting signals from both under and over-exertion.”
In the traditional method, electrodes are made into an unchangeable structure with predesigned stretchability. In contrast, the new supercapacitors that NTU scientists developed can be edited into different shapes and structures and stretched in different directions. (Image: NTU)
The editable supercapacitor is made of strengthened manganese dioxide nanowire composite material. While manganese dioxide is a common material for supercapacitors, the ultralong nanowire structure, strengthened with a network of carbon nanotubes and nanocellulose fibres, allows the electrodes to withstand the associated strains during the customisation process.
The NTU team also collaborated with Dr. Loh Xian Jun, Senior Scientist and Head of the Soft Materials Department at the Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR).
Dr. Loh said, “Customisable and versatile, these interconnected, fabric-like power sources are able to offer a plug-and-play functionality while maintaining good performance. Being highly stretchable, these flexible power sources are promising next-generation ‘fabric’ energy storage devices that could be integrated into wearable electronics.”
Lupta împotriva cariilor dentare primește ajutor cu un nou material inteligent nanocompozit.Cu unele reglaje fine, acest nou material „inteligent” ar putea crea o umplere mai puternică și mai puține excursii la dentist.
Posted: Jan 30, 2018
The fight against tooth decay gets help with a new nanocomposite smart material
(Nanowerk News) When patients go to the dentist to fill a cavity, they’re trying to solve a problem — not create a new one. But many dental patients get some bad news: bacteria can dig under their tooth-coloured fillings and cause new cavities, called recurrent caries. These recurrent caries affect 100 million patients every year and cost an additional US$34 billion to treat.
Now, a research collaboration between the Department of Materials Science & Engineering (MSE), Faculty of Dentistry, and the Institute of Biomaterials and Biomedical Engineering (IBBME) at the University of Toronto has resulted in a novel way to minimize recurrent caries.
In a recent paper published in the journal Scientific Reports („Drug self-assembly for synthesis of highly-loaded antimicrobial drug-silica particles”), professors Ben Hatton (MSE), Yoav Finer (Dentistry) and PhD student Cameron Stewart (IBBME) tackled the issue and proposed a novel solution: a filling material with tiny particles made by self-assembly of antimicrobial drugs, designed to stop bacteria in its tracks. These particles may solve one of the biggest problems with antibacterial filling materials: how do you store enough drug within the material to be effective for someone’s entire life?
“Adding particles packed with antimicrobial drugs to a filling creates a line of defense against cavity-causing bacteria,” says Hatton. “But traditionally there’s only been enough drug to last a few weeks. Through this research we discovered a combination of drugs and silica glass that organize themselves on a molecule-by-molecule basis to maximize drug density, with enough supply to last years.” This discovery of using antimicrobials which self-assemble means the team can pack 50 times as much of the bacteria-fighting drugs into the particles.
“We know very well that bacteria specifically attack the margins between fillings and the remaining tooth to create cavities,” says Finer. “Giving these materials an antimicrobial supply that will last for years could greatly reduce this problem.”
Looking ahead, the research team plans on testing these new drug-storing particles in dental fillings, monitoring their performance when attacked by bacteria and saliva in the complex environment in the mouth. With some fine-tuning, this new ‘smart’ material could create a stronger filling and fewer trips to the dentist.
„Microelementele verticale flexibile verticale pot fi utilizate în ceasuri inteligente cu consum redus de energie, afișaje mobile și iluminat ușor de purtat. În plus, aceste dispozitive optoelectrice flexibile sunt potrivite pentru aplicații biomedicale, cum ar fi știința creierului, tratamentul fototerapeutic și lentilele de contact biosenzori.“
Posted: Jan 29, 2018
Researchers develop flexible vertical micro LED (w/video)
(Nanowerk News) A Korea Advanced Institute of Science and Technology (KAIST) research team led by Professor Keon Jae Lee from the Department of Materials Science and Engineering and Professor Daesoo Kim from the Department of Biological Sciences has developed flexible vertical micro LEDs (f-VLEDs) using anisotropic conductive film (ACF)-based transfer and interconnection technology. The team also succeeded in controlling animal behavior via optogenetic stimulation of the f-VLEDs.
Flexible micro LEDs have become a strong candidate for the next-generation display due to their ultra-low power consumption, fast response speed, and excellent flexibility. However, the previous micro LED technology had critical issues such as poor device efficiency, low thermal reliability, and the lack of interconnection technology for high-resolution micro LED displays.
The research team has designed new transfer equipment and fabricated a f-VLED array (50×50) using simultaneous transfer and interconnection through the precise alignment of ACF bonding process. These f-VLEDs achieved optical power density (30 mW/mm2) three times higher than that of lateral micro LEDs, improving thermal reliability and lifetime by reducing heat generation within the thin film LEDs.
These f-VLEDs (thickness: 5 micrometre, size: below 80 micrometre) can be applied to optogenetics for controlling the behavior of neuron cells and brains. In contrast to the electrical stimulation that activates all of the neurons in brain, optogenetics can stimulate specific excitatory or inhibitory neurons within the localized cortical areas of the brain, which facilitates precise analysis, high-resolution mapping, and neuron modulation of animal brains. (Refer to the author’s previous ACS Nano paper „Optogenetic Mapping of Functional Connectivity in Freely Moving Mice via Insertable Wrapping Electrode Array Beneath the Skull”)
In this work, they inserted the innovative f-VLEDs into the narrow space between the skull and the brain surface and succeeded in controlling mouse behavior by illuminating motor neurons on two-dimensional cortical areas located deep below the brain surface.
Comparison of micro-LEDs Technology. (IMage: KAIST)
Professor Lee said, „The flexible vertical micro LED can be used in low-power smart watches, mobile displays, and wearable lighting. In addition, these flexible optoelectronic devices are suitable for biomedical applications such as brain science, phototherapeutic treatment, and contact lens biosensors.”
au creat un tip complet nou de mușchi moleculară artificială dintr-un polimer capabil de ridicare greu;Cercetătorii se uită acum la modul în care își pot împerechea polimerul funcțional nou cu alții care sunt mai rezistenți și capabili să ridice sarcini mai grele. Ei vor, de asemenea, să dau seama cum să controleze mușchii artificiale moleculare folosind electrozi. Această acțiune ar fi similară cu modul în care semnalele electrice sunt transmise în organism și ar putea deschide calea spre viitoarele aplicații protetice.
Posted: Jan 29, 2018
New molecular muscle responds to visible light
(Nanowerk News) Picture a tiny, makeshift muscle that can curl a 20 milligram suspended weight when exposed to light. Under the right conditions, another mix packs enough power to bench-press a dime.
Researchers at Washington University in St. Louis have created a completely new kind of artificial molecular muscle from a polymer that’s capable of some heavy lifting — relatively speaking.
“The external trigger that initiates the actuation process can be something as simple as sunlight,” said Jonathan Barnes, assistant professor of chemistry in Arts & Sciences and a 2017 Packard Fellow. The novel polymer, which changes color and contracts when exposed to visible light, is described in a Jan. 24 publication of a special issue of Macromolecular Rapid Communications(„Photoredox-Based Actuation of an Artificial Molecular Muscle”).
The polymer was attached to a slip of black electrical tape. Exposed to blue light, the artificial molecular muscle moved a 20 milligram weight several centimeters from its starting position. (Image: Barnes laboratory, Washington University in St. Louis)
Barnes and his team have been working on their proof of concept for the novel redox-responsive polymer — one that contracts when electrons are added (reduction) and expands when they are taken away (oxidation) — since he started at Washington University less than two years ago.
Last fall, they demonstrated that they could successfully build their functional polymer and incorporate it into a pliant, bulk material called a hydrogel. The resulting material could be contracted to one-tenth its original volume and then expanded back to its original size, its long polymer chains delicately folding and unfolding in three dimensions.
The hydrogel contains 5 percent polymer overall, of which only 5 percent is the new, functional polymer; the rest is just water. This means that only 0.25 percent of the total hydrogel is the functional polymer, an incredibly low number in the field.
“If you look at other materials, the active polymer is usually in every link,” said Angelique Greene, a postdoctoral fellow in the Barnes laboratory. “Ours is very dilute, and yet our hydrogels still performed at a comparable and sometimes even better rate.”
Pulling their own weight
But the molecular muscle still needed to be triggered by chemical reduction in a wet solution. To address the slosh factor, the researchers then introduced visible-light-absorbing photoredox catalysts, embedded in the gel, and moved their muscles onto dry ground.
It was time for a strength test.
“We wanted to demonstrate that it could not only change shape, or bend, or turn a different color, but actually do work,” Barnes said.
The researchers affixed their best-performing gel to a piece of black electrical tape, and then attached a small, light piece of aluminum wire holding a small 20 milligram weight on the bottom. They exposed it to a blue light, and, after five hours, the polymer had moved the suspended weight several centimeters from its starting position.
“Here we have a lot fine control,” said Kevin Liles, a PhD candidate in chemistry who co-wrote the new study, along with Greene. “We can irradiate the polymer for a certain amount of time, stop it at a certain number of degrees (of bend), or irradiate a certain portion and get it to contract in certain areas.”
Five hours might seem like a long time to move a few centimeters, but Barnes isn’t worried that Mother Nature does it faster.
“If you’ve ever seen a flower or plant on the side of a mountain, it always bends toward where the light is,” Barnes said. “Nature finds a way to adapt to optimize the amount of light source that hits its petals. This material in principle does the exact same thing.”
The researchers are now looking at how to pair their novel functional polymer with others that are tougher and capable of lifting heavier loads. They also want to figure out how to control the artificial molecular muscles using electrodes. This action would be similar to the way that electrical signals are transmitted in the body, and could pave the way toward future prosthetic applications.
Cercetătorii au demonstrat cum să creeze un aliaj de aluminiu super-puternic care rivalizează rezistența oțelului inoxidabil, un avans cu potențiale aplicații industriale.Acoperirile din aliaj de aluminiu-fier rezultat „nanotwinned” s-au dovedit a fi unul dintre cele mai puternice aliaje de aluminiu create vreodată, comparabile cu oțelurile cu rezistență ridicată.
Posted: Jan 26, 2018
New research yields super-strong aluminum alloy
(Nanowerk News) Researchers have demonstrated how to create a super-strong aluminum alloy that rivals the strength of stainless steel, an advance with potential industrial applications.
“Most lightweight aluminum alloys are soft and have inherently low mechanical strength, which hinders more widespread industrial application,” said Xinghang Zhang, a professor in Purdue University’s School of Materials Engineering. “However, high-strength, lightweight aluminum alloys with strength comparable to stainless steels would revolutionize the automobile and aerospace industries.”
New research shows how to alter the microstructure of aluminum to impart greater strength and ductility. Findings were detailed in two new research papers. The work was led by a team of researchers that included Purdue postdoctoral research associate Sichuang Xue and doctoral student Qiang Li.
A sample is readied for analysis using a transmission electron microscope. (Image: Marshall Farthing)
The new high-strength aluminum is made possible by introducing “stacking faults,” or distortions in the crystal structure. While these are easy to produce in metals such as copper and silver, they are difficult to introduce in aluminum because of its high “stacking fault energy.”
A metal’s crystal lattice is made up of a repeating sequence of atomic layers. If one layer is missing, there is said to be a stacking fault. Meanwhile, so-called “twin boundaries” consisting of two layers of stacking faults can form. One type of stacking fault, called a 9R phase, is particularly promising, Zhang said.
“It has been shown that twin boundaries are difficult to be introduced into aluminum. The formation of the 9R phase in aluminum is even more difficult because of its high stacking fault energy,” Zhang said. “You want to introduce both nanotwins and 9R phase in nanograined aluminum to increase strength and ductility and improve thermal stability.”
Now, researchers have learned how to readily achieve this 9R phase and nanotwins in aluminum.
“These results show how to fabricate aluminum alloys that are comparable to, or even stronger than, stainless steels,” he said. “There is a lot of potential commercial impact in this finding.”
Xue is lead author of the Nature Communications paper, which is the first to report a “shock-induced” 9R phase in aluminum. Researchers bombarded ultrathin aluminum films with tiny micro-projectiles of silicon dioxide, yielding 9R phase.
“Here, by using a laser-induced projectile impact testing technique, we discover a deformation-induced 9R phase with tens of nanometers in width,” Xue said.
The microprojectile tests were performed by a research group at Rice University, led by professor Edwin L. Thomas, a co-author of the Nature Communications paper. A laser beam causes the particles to be ejected at a velocity of 600 meters per second. The procedure dramatically accelerates screening tests of various alloys for impact-resistance applications.
“Say I want to screen many materials within a short time,” Zhang said. “This method allows us to do that at far lower cost than otherwise possible.”
Li is lead author of the Advanced Materials paper, which describes how to induce a 9R phase in aluminum not by shock but by introducing iron atoms into aluminum’s crystal structure via a procedure called magnetron sputtering. Iron also can be introduced into aluminum using other techniques, such as casting, and the new finding could potentially be scaled up for industrial applications.
The resulting “nanotwinned” aluminum-iron alloy coatings proved to be one of the strongest aluminum alloys ever created, comparable to high-strength steels.
“Molecular-dynamics simulations, performed by professor Jian Wang’s group at the University of Nebraska, Lincoln, showed the 9R phase and nanograins result in high strength and work-hardening ability and revealed the formation mechanisms of the 9R phase in aluminum,” Zhang said. “Understand new deformation mechanisms will help us design new high strength, ductile metallic materials, such as aluminum alloys.”
One potential application might be to design wear- and corrosion-resistant aluminum alloy coatings for the electronics and automobile industries.
Se dezvăluie un proces de reciclare ecologic pentru deșeurile din polistiren expandat (EPS), utilizând procesul de dizolvare și procesul de extracție CO 2 supercritică . Procesul de reciclare poate permite condensarea unui polistiren expandat (EPS) prin dizolvarea EPS într-un solvent și unul sau mai mulți aditivi, obținându-se astfel o soluție de polistiren expandat (EPS). Procesul de reciclare poate permite în continuare purificarea soluției EPS folosind cel puțin un procedeu de filtrare și un proces de separare pentru a obține o soluție de polistiren expandat purificat (EPS). Mai mult, procesul de reciclare poate permite extragerea polistirenului din solvent în soluția de polistiren expandat purificat (EPS) folosind un CO 2 supercriticmetoda de extracție pentru obținerea unui polistiren reciclat. Procesul de reciclare permite reducerea semnificativă a volumului EPS, economisind astfel costurile logistice, precum și facilitarea creșterii cantității, calității și purității polistirenului reciclat.
