Echipa de știință a materialelor Sandia a elaborat un aliaj de aur de platină, considerat a fi cel mai rezistent metal din lume. Este de 100 de ori mai durabil decât oțelul de înaltă rezistență, făcându-l primul aliaj sau o combinație de metale, în aceeași clasă ca diamantele și safirul, cele mai rezistente la uzură materiale ale naturii.
Posted: Aug 16, 2018
Engineers develop world’s most wear-resistant metal alloy
(Nanowerk News) If you’re ever unlucky enough to have a car with metal tires, you might consider a set made from a new alloy engineered at Sandia National Laboratories. You could skid — not drive, skid — around the Earth’s equator 500 times before wearing out the tread.
Sandia’s materials science team has engineered a platinum-gold alloy believed to be the most wear-resistant metal in the world. It’s 100 times more durable than high-strength steel, making it the first alloy, or combination of metals, in the same class as diamond and sapphire, nature’s most wear-resistant materials. Sandia’s team recently reported their findings in Advanced Materials(„Achieving Ultralow Wear with Stable Nanocrystalline Metals”). “We showed there’s a fundamental change you can make to some alloys that will impart this tremendous increase in performance over a broad range of real, practical metals,” said materials scientist Nic Argibay, an author on the paper.
Although metals are typically thought of as strong, when they repeatedly rub against other metals, like in an engine, they wear down, deform and corrode unless they have a protective barrier, like additives in motor oil.
In electronics, moving metal-to-metal contacts receive similar protections with outer layers of gold or other precious metal alloys. But these coatings are expensive. And eventually they wear out, too, as connections press and slide across each other day after day, year after year, sometimes millions, even billions of times. These effects are exacerbated the smaller the connections are, because the less material you start with, the less wear and tear a connection can endure before it no longer works.
With Sandia’s platinum-gold coating, only a single layer of atoms would be lost after a mile of skidding on the hypothetical tires. The ultradurable coating could save the electronics industry more than $100 million a year in materials alone, Argibay says, and make electronics of all sizes and across many industries more cost-effective, long-lasting and dependable — from aerospace systems and wind turbines to microelectronics for cell phones and radar systems.
“These wear-resistant materials could potentially provide reliability benefits for a range of devices we have explored,” said Chris Nordquist, a Sandia engineer not involved in the study. “The opportunities for integration and improvement would be device-specific, but this material would provide another tool for addressing current reliability limitations of metal microelectronic components.”
New metal puts an old theory to rest
You might be wondering how metallurgists for thousands of years somehow missed this. In truth, the combination of 90 percent platinum with 10 percent gold isn’t new at all.
But the engineering is new. Argibay and coauthor Michael Chandross masterminded the design and the new 21st century wisdom behind it. Conventional wisdom says a metal’s ability to withstand friction is based on how hard it is. The Sandia team proposed a new theory that says wear is related to how metals react to heat, not their hardness, and they handpicked metals, proportions and a fabrication process that could prove their theory.
“Many traditional alloys were developed to increase the strength of a material by reducing grain size,” said John Curry, a postdoctoral appointee at Sandia and first author on the paper. “Even still, in the presence of extreme stresses and temperatures many alloys will coarsen or soften, especially under fatigue. We saw that with our platinum-gold alloy the mechanical and thermal stability is excellent, and we did not see much change to the microstructure over immensely long periods of cyclic stress during sliding.”
Now they have proof they can hold in their hands. It looks and feels like ordinary platinum, silver-white and a little heavier than pure gold. Most important, it’s no harder than other platinum-gold alloys, but it’s much better at resisting heat and a hundred times more wear resistant.
The team’s approach is a modern one that depended on computational tools. Argibay and Chandross’ theory arose from simulations that calculated how individual atoms were affecting the large-scale properties of a material, a connection that’s rarely obvious from observations alone. Researchers in many scientific fields use computational tools to take much of the guesswork out of research and development.
“We’re getting down to fundamental atomic mechanisms and microstructure and tying all these things together to understand why you get good performance or why you get bad performance, and then engineering an alloy that gives you good performance,” Chandross said.
A slick surprise
Still, there will always be surprises in science. In a separate paper published in Carbon („In situ tribochemical formation of self-lubricating diamond-like carbon films”), the Sandia team describes the results of a remarkable accident. One day, while measuring wear on their platinum-gold, an unexpected black film started forming on top. They recognized it: diamond-like carbon, one of the world’s best man-made coatings, slick as graphite and hard as diamond. Their creation was making its own lubricant, and a good one at that.
Diamond-like carbon usually requires special conditions to manufacture, and yet the alloy synthesized it spontaneously.
“We believe the stability and inherent resistance to wear allows carbon-containing molecules from the environment to stick and degrade during sliding to ultimately form diamond-like carbon,” Curry said. “Industry has other methods of doing this, but they typically involve vacuum chambers with high temperature plasmas of carbon species. It can get very expensive.”
The phenomenon could be harnessed to further enhance the already impressive performance of the metal, and it could also potentially lead to a simpler, more cost-effective way to mass-produce premium lubricant.
O echipă de ingineri de la Universitatea din Delaware dezvoltă produse inteligente de generație următoare, prin crearea de straturi compozite de nanotuburi de carbon flexibile pe o gamă largă de fibre, inclusiv bumbac, nailon și lână.Nanotuburile de carbon conferă această capacitate impresionantă de detectare ușoară, flexibilă și respirabilă. Când materialul este stors, se măsoară cu ușurință modificări electrice mari ale materialului.
Posted: Aug 16, 2018
Novel nanotechnology sensors could enable smarter textiles
(Nanowerk News) A team of engineers at the University of Delaware is developing next-generation smart textiles by creating flexible carbon nanotube composite coatings on a wide range of fibers, including cotton, nylon and wool. Their discovery is reported in the journal ACS Sensors („Thin and Flexible Carbon Nanotube-Based Pressure Sensors with Ultrawide Sensing Range”) where they demonstrate the ability to measure an exceptionally wide range of pressure – from the light touch of a fingertip to being driven over by a forklift.
Fabric coated with this sensing technology could be used in future “smart garments” where the sensors are slipped into the soles of shoes or stitched into clothing for detecting human motion.
Sagar Doshi (left) and Erik Thostenson test an elbow sleeve outfitted with one of their novel sensors. (Image: University of Delaware)
Carbon nanotubes give this light, flexible, breathable fabric coating impressive sensing capability. When the material is squeezed, large electrical changes in the fabric are easily measured.
“As a sensor, it’s very sensitive to forces ranging from touch to tons,” said Erik Thostenson, an associate professor in the Departments of Mechanical Engineering and Materials Science and Engineering.
Nerve-like electrically conductive nanocomposite coatings are created on the fibers using electrophoretic deposition (EPD) of polyethyleneimine functionalized carbon nanotubes.
“The films act much like a dye that adds electrical sensing functionality,” said Thostenson. “The EPD process developed in my lab creates this very uniform nanocomposite coating that is strongly bonded to the surface of the fiber. The process is industrially scalable for future applications.”
Now, researchers can add these sensors to fabric in a way that is superior to current methods for making smart textiles. Existing techniques, such as plating fibers with metal or knitting fiber and metal strands together, can decrease the comfort and durability of fabrics, said Thostenson, who directs UD’s Multifunctional Composites Laboratory.
The nanocomposite coating developed by Thostenson’s group is flexible and pleasant to the touch and has been tested on a range of natural and synthetic fibers, including Kevlar, wool, nylon, Spandex and polyester. The coatings are just 250 to 750 nanometers thick — about 0.25 to 0.75 percent as thick as a piece of paper — and would only add about a gram of weight to a typical shoe or garment. What’s more, the materials used to make the sensor coating are inexpensive and relatively eco-friendly, since they can be processed at room temperature with water as a solvent.
Exploring Future Applications
One potential application of the sensor-coated fabric is to measure forces on people’s feet as they walk. This data could help clinicians assess imbalances after injury or help to prevent injury in athletes. Specifically, Thostenson’s research group is collaborating with Jill Higginson, professor of mechanical engineering and director of the Neuromuscular Biomechanics Lab at UD, and her group as part of a pilot project funded by Delaware INBRE. Their goal is to see how these sensors, when embedded in footwear, compare to biomechanical lab techniques such as instrumented treadmills and motion capture.
During lab testing, people know they are being watched, but outside the lab, behavior may be different.
“One of our ideas is that we could utilize these novel textiles outside of a laboratory setting — walking down the street, at home, wherever,” said Thostenson.
Sagar Doshi, a doctoral student in mechanical engineering at UD, is the lead author on the paper. He worked on making the sensors, optimizing their sensitivity, testing their mechanical properties and integrating them into sandals and shoes. He has worn the sensors in preliminary tests, and so far, the sensors collect data that compares with that collected by a force plate, a laboratory device that typically costs thousands of dollars.
“Because the low-cost sensor is thin and flexible the possibility exists to create custom footwear and other garments with integrated electronics to store data during their day-to-day lives,” Doshi said. “This data could be analyzed later by researchers or therapists to assess performance and ultimately bring down the cost of healthcare.”
This technology could also be promising for sports medicine applications, post-surgical recovery, and for assessing movement disorders in pediatric populations.
“It can be challenging to collect movement data in children over a period of time and in a realistic context,” said Robert Akins, Director of the Center for Pediatric Clinical Research and Development at the Nemours – Alfred I. duPont Hospital for Children in Wilmington and affiliated professor of materials science and engineering, biomedical engineering and biological sciences at UD. “Thin, flexible, highly sensitive sensors like these could help physical therapists and doctors assess a child’s mobility remotely, meaning that clinicians could collect more data, and possibly better data, in a cost-effective way that requires fewer visits to the clinic than current methods do.”
Interdisciplinary collaboration is essential for the development of future applications, and at UD, engineers have a unique opportunity to work with faculty and students from the College of Health Sciences on UD’s Science, Technology and Advanced Research (STAR) Campus.
“As engineers, we develop new materials and sensors but we don’t always understand the key problems that doctors, physical therapists and patients are facing,” said Doshi. “We collaborate with them to work on the problems they are facing and either direct them to an existing solution or create an innovative solution to solve that problem.”
Thostenson’s research group also uses nanotube-based sensors for other applications, such as structural health monitoring.
“We’ve been working with carbon nanotubes and nanotube-based composite sensors for a long time,” said Thostenson, who is affiliated faculty at UD’s Center for Composite Materials (UD-CCM). Working with researchers in civil engineering his group has pioneered the development of flexible nanotube sensors to help detect cracks in bridges and other types of large-scale structures.
“One of the things that has always intrigued me about composites is that we design them at varying lengths of scale, all the way from the macroscopic part geometries, an airplane or an airplane wing or part of a car, to the fabric structure or fiber level. Then, the nanoscale reinforcements like carbon nanotubes and graphene give us another level to tailor the material structural and functional properties. Although our research may be fundamental, there is always an eye towards applications. UD-CCM has a long history of translating fundamental research discoveries in the laboratory to commercial products through UD-CCM’s industrial consortium.”
Lucrările lor introduc o nouă clasă de sisteme nanocrystal-in-glass, care sporesc eficiența optoelectronicii, cum ar fi fotovoltaica și divizarea apelor induse de lumină.Această strategie va ajuta la proiectarea unor nanomateriale personalizate. Cercetătorii sugerează acum să utilizeze strategia prezentată pentru nanocompozitele semiconductoare relevante din punct de vedere tehnologic și sistemele nanoparticule în sticlă.
Posted: Aug 15, 2018
Designing nanocrystals for more efficient optoelectronics
(Nanowerk News) New artificial materials for semiconductors used in solar cells or photoelectrochemical cells that are designed from scratch with totally new and tailored properties: this is the latest research topic of Stefan Wippermann, head of the group “Atomistic Modelling“ at the Max-Planck-Institut für Eisenforschung), and his team. They characterized for the first time with atomic resolution a typical material system and are able to set design principles.
Their work introduces a new class of nanocrystal-in-glass systems, which increase the efficiency of optoelectronics such as photovoltaics and light-induced water splitting.
The luminescent atoms in the image show a nanocrystal which is characterized with atomistic resolution, including its interface chemistry. (Image: Peter Allen)
Nanocrystals can be used as “artificial atoms” to create designer materials for electronic applications and solar energy conversion as they are controllable, potentially non-toxic and earth-abundant. In collaboration with the groups of Dmitri Talapin and Giulia Galli, University of Chicago, wet-chemical techniques were used to synthesize those nanocrystals and assemble them into semiconducting nanocomposites.
“One great advantage of designing nanocrystals is that we are able to choose their properties”, explains Wippermann. “As we develop our own “atoms”, we do not rely anymore on the chemical properties of elements but are able to design materials with target properties through nanostructuring.”
That means the researchers can abstain for example from toxic or rare elements. And even though their current model system is still using toxic elements, they embed the nanocrystals into solid matrices so that the nanocrystals are not spread into air.
“The current key challenge is not the production of the nanocrystals themselves but rather the understanding and controlling of their interface chemistry and defects, as their surfaces and interfaces are only a few nanometres in size and buried inside the material”, says Wippermann.
He and his team produced and analysed buried interfaces in solids of indium arsenide nanoparticles capped with thiostannate (Sn2S64-) ligands as prototypical nanocomposites. The ligands are used during the synthesis of the nanocomposites. With the help of theoretical and experimental techniques they found that the ligands are not adsorbed as intact units but decompose upon contact with the nanocrystal surface, forming an amorphous matrix around the nanocrystals.
Exactly this matrix influences the electronic transport of the nanocrystal solids, as the decomposed ligands form a passivation layer on the nanocrystal surface and only on top of this layer an intact ligand may adsorb.
Indium arsenide nanocrystals embedded in amorphous SnS3. Magenta and violet balls, green and yellow tubes denote indium, arsenic, tin and sulphur atoms, respectively. A sulphur chain in red. (Image: Stefan Wippermann)
Another passivation mechanism is the incorporation of sulphur into the subsurface layer. Arsenic in turn diffuses into the matrix, leading to the formation of characteristic defects. These defects explain the observed switching between positive and negative photoconductivity. Simulations showed that the indium arsenide nanocrystals draw sulphur from the matrix leading to the formation of a sulphur shell around the nanocrystals.
Sulphur also affects the amount and character of defects in the nanocomposite: A high sulphur content reduces the number of dangling bond defects in the nanocomposite and leads to the formation of sulphur chains acting as hole-conducting interconnects between the nanocrystals.
The Max Planck scientists show that the properties of nanocrystal-based solids are influenced by the size, shape, composition, surface chemistry and mutual interactions of nanocrystals. The strong quantum confinement of charge carriers inside the nanocrystals enable efficient carrier multiplication, where a single high energy photon creates multiple electron-hole pairs, which contribute to the conductivity.
This way optoelectronics can be made more efficient. Nanocrystals capped with molecular metal chalcogenide complexes have especially high electron mobilities, which allow for fast extraction of the photogenerated charges. The scientists established a strategy to characterize buried interfaces in inorganic nanocomposites and more generally nanoparticle-in-glass systems.
This strategy will help in designing tailor-made nanomaterials. The researchers now suggests to employ the presented strategy to technologically relevant semiconductor nanocomposites and nanoparticle-in-glass systems.
Laboratorul Rice al inginerului chimic Sibani, Lisa Biswal, a realizat un compus cu nanoparticule magnetice care separă eficient picăturile de țiței din apa produsă, care s-au dovedit dificil de îndepărtat prin metodele actuale.Nanoparticulele magnetice trag ultimele picături de ulei din apele din puț
Posted: Aug 15, 2018
Magnetic nanoparticles pull last drops of oil from well water
(Nanowerk News) Oil and water tend to separate, but they mix well enough to form stable oil-in-water emulsions in produced water from oil reservoirs to become a problem. Rice University scientists have developed a nanoparticle-based solution that reliably removes more than 99 percent of the emulsified oil that remains after other processing is done.
The Rice lab of chemical engineer Sibani Lisa Biswal made a magnetic nanoparticle compound that efficiently separates crude oil droplets from produced water that have proven difficult to remove with current methods.
Rice University engineers have developed magnetic nanoparticles that separate the last droplets of oil from produced water at wells. The particles draw in the bulk of the oil and are then attracted to the magnet, as demonstrated here. (Image:Jeff Fitlow)
Produced water comes from production wells along with oil. It often includes chemicals and surfactants pumped into a reservoir to push oil to the surface from tiny pores or cracks, either natural or fractured, deep underground. Under pressure and the presence of soapy surfactants, some of the oil and water form stable emulsions that cling together all the way back to the surface.
While methods exist to separate most of the oil from the production flow, engineers at Shell Global Solutions, which sponsored the project, told Biswal and her team that the last 5 percent of oil tends to remain stubbornly emulsified with little chance to be recovered.
“Injected chemicals and natural surfactants in crude oil can oftentimes chemically stabilize the oil-water interface, leading to small droplets of oil in water which are challenging to break up,” said Biswal, an associate professor of chemical and biomolecular engineering and of materials science and nanoengineering.
The Rice lab’s experience with magnetic particles and expertise in amines, courtesy of former postdoctoral researcher and lead author Qing Wang, led it to combine techniques. The researchers added amines to magnetic iron nanoparticles. Amines carry a positive charge that helps the nanoparticles find negatively charged oil droplets. Once they do, the nanoparticles bind the oil. Magnets are then able to pull the droplets and nanoparticles out of the solution.
“It’s often hard to design nanoparticles that don’t simply aggregate in the high salinities that are typically found in reservoir fluids, but these are quite stable in the produced water,” Biswal said.
The enhanced nanoparticles were tested on emulsions made in the lab with model oil as well as crude oil.
In both cases, researchers inserted nanoparticles into the emulsions, which they simply shook by hand and machine to break the oil-water bonds and create oil-nanoparticle bonds within minutes. Some of the oil floated to the top, while placing the test tube on a magnet pulled the infused nanotubes to the bottom, leaving clear water in between.
Best of all, Biswal said, the nanoparticles can be washed with a solvent and reused while the oil can be recovered. The researchers detailed six successful charge-discharge cycles of their compound and suspect it will remain effective for many more.
She said her lab is designing a flow-through reactor to process produced water in bulk and automatically recycle the nanoparticles. That would be valuable for industry and for sites like offshore oil rigs, where treated water could be returned to the ocean.
) Imprimarea 3D prin scrierea directă cu laser permite producerea de structuri cu dimensiuni micro-metrice pentru multe aplicații, de la biomedicină la microelectronică până la metamateriale optice. Cercetătorii de la Institutul de Tehnologie din Karlsruhe (KIT) au dezvoltat acum cerneluri 3D care pot fi șterse selectiv. Acest lucru permite degradarea și reasamblarea specifică a structurilor foarte precise pe micrometrele și pe scalele nanometrice.
Posted: Aug 14, 2018
3D inks that can be erased selectively
(Nanowerk News) 3D printing by direct laser writing enables production of micro-meter-sized structures for many applications, from biomedicine to microelectronics to optical metamaterials. Researchers of Karlsruhe Institute of Technology (KIT) have now developed 3D inks that can be erased selectively. This allows specific degradation and reassembly of highly precise structures on the micrometer and nanometer scales.
3D printing is gaining importance, as it allows for the efficient manufacture of complex geometries. A very promising method is direct laser writing: a computer-controlled focused laser beam acts as a pen and produces the desired structure in a photoresist. In this way, three-dimensional structures with details in the sub-micrometer range can be produced.
“The high resolution is very attractive for applications requiring very precise filigree structures, such as in biomedicine, microfluidics, microelectronics or for optical metamaterials,” say Professor Christopher Barner-Kowollik, Head of the Macromolecular Architectures Group of KIT’s Institute for Chemical Technology and Polymer Chemistry (ITCP) and of the Soft Matter Materials Group of Queensland University of Technology (QUT) in Brisbane, Australia, and Dr. Eva Blasco of the ITCP of KIT.
Over a year ago, KIT researchers already succeeded in expanding the possibilities of direct laser writing: the working groups of Professor Martin Wegener at the Institute of Applied Physics (APH) and the Institute of Nanotechnology (INT) of KIT and of Professor Christopher Barner-Kowollik developed an erasable ink for 3D printing. Thanks to reversible binding, the building blocks of the ink can be separated again.
Now, the scientists from Karlsruhe and Brisbane have largely refined their development. As reported in the journal Nature Communications, they have developed several inks, in different colors so to speak, that can be erased independently of each other. This enables selective and sequential degradation and reassembly of the laser-written microstructures.
In case of highly complex constructions, for instance, temporary supports can be produced and removed again later on. It may also be possible to add or remove parts to or from three-dimensional scaffolds for cell growth, the objective being to observe how the cells react to such changes. Moreover, the specifically erasable 3D inks allow for the exchange of damaged or worn parts in complex structures.
When producing the cleavable photoresists, the researchers were inspired by degradable biomaterials. The photoresists are based on silane compounds that can be cleaved easily. Silanes are silicon-hydrogen compounds. The scientists used specific atom substitution for preparing the photoresists. In this way, microstructures can be degraded specifically under mild conditions without structures with other material properties being damaged.
This is the major advantage over formerly used erasable 3D inks. New photoresists also contain the monomer pentaerythritol triacrylate that significantly enhances writing without affecting cleavability.
Aceste progrese, făcute de mediul colaborativ al platformei Grafene, ar putea conduce la aplicații promițătoare în senzori, în optoelectronică și în dispozitive flexibile. Cercetătorii visează acum dispozitive hibride multifuncționale de înaltă performanță sub controlul celei mai abundente și puternice surse de lumină energetică a naturii.Această moleculă – un spiropyran capabil să poată fi redată prin imagine – poate fi apoi ancorată la suprafața materialelor cum ar fi grafenul sau disulfura de molibden, generând astfel o superlattică macroscopică hibridă precis atomică. Când este iluminat, întreaga structură supramoleculară are o rearanjare structurală colectivă, care poate fi vizualizată direct cu o rezoluție sub-nanometrică prin scanarea microscopiei de tunel.
Posted: Aug 14, 2018
Flipping the switch on supramolecular electronics
(Nanowerk News) Graphene and related materials hold great potential for technological applications such as electronics, sensors, and energy storage devices, among others. Thanks to their high surface sensitivity, these materials are an ideal platform to study the interplay between molecular assemblies at the nanoscale and macroscopic electrical phenomena.
This molecule – a photoswitchable spiropyran – can be then anchored to the surface of materials such as graphene or molybdenum disulfide, thus generating an atomically precise hybrid macroscopic superlattice. When illuminated, the whole supramolecular structure experiences a collective structural rearrangement, which could be directly visualized with a sub-nanometer resolution by scanning tunneling microscopy.
More importantly, this light-induced reorganization at the molecular level induces large changes in the macroscopic electrical properties of the hybrid devices. The molecules, together with the layers of graphene and related materials, can convert single-molecule events into a spatially homogeneous switching action that generates a macroscopic electrical response. This novel and versatile approach takes supramolecular electronics to the next level.
Photo-switchable molecular crystals in two dimensions. (click on image to enlarge)
‘Thanks to this new approach, we can exploit the capacity of collective switching events occurring in superlattices of photochromic molecules assembled onto graphene and related materials to induce large scale and reversible modulation in the electrical properties of high-performance opto-electronic devices,’ explains Paolo Samorì, lead author of the paper. ‘This technology could find applications in the next generation of smart and portable electronics, with programmable properties,’ he adds.
Samorì also explains how this idea of tailoring molecular superlattices could generate a wide variety of new materials with tunable and responsive properties. ‘To dial your functions! You only need to carefully choose the right molecules, the thus-formed superlattice will allow to maximize the change in properties as a response to external inputs,’ he says.
Vittorio Pellegrini, researcher at IIT and Division Leader for Energy, Composites, and Production at the Graphene Flagship, highlights how the research is ‘unique in the way it combines graphene and other related materials with light-responsive chemical molecules. These macroscopic arrangements are promising platforms for optoelectronics.’ Pellegrini points out the outstanding potential of these new findings: ‘the molecular ultra-thin coating can be tailored just by synthesizing different molecules.’ Moreover, ‘this discovery will lead us to the development of devices, as the technique developed by Samorì and his team can be scaled up in reproducible manner,’ he added. Samorì agrees: ‘The limit in the scalability is the accessibility to ultra-flat and atomically precise graphene and related materials.’
These advances, made possible by the collaborative environment of the Graphene Flagship, could lead to promising applications in sensors, optoelectronics, and flexible devices. Researchers now dream of high-performance multifunctional hybrid devices under control of nature’s most abundant and powerful source of energy – light.
Professor Andrea C. Ferrari, Science and Technology Officer of the Graphene Flagship, and Chair of its management panel added: ‘Supra-molecular chemistry has been part of the Flagship research since the very beginning. Over the years our partners have improved and developed the techniques that enable to interface molecules with graphene and related materials. We are now witnessing a steady progress towards applications, as shown by this interesting work.’
Un gel nou, super-izolator dezvoltat de cercetatorii de la Universitatea din Colorado Boulder ar putea creste dramatic eficienta energetica a zgarie-nori si a altor cladiri si ar putea ajuta intr-o zi oamenii de stiinta sa construiasca habitate de sera pentru coloniști pe Marte. „Aerogelul”, care seamănă cu o lentilă de contact plată din plastic, este atât de rezistent la căldură încât să-i poți pune o bandă pe mâna ta și să aprinzi focul fără să simți nimic
Posted: Aug 13, 2018
From office windows to Mars: Scientists debut super-insulating gel
(Nanowerk News) A new, super-insulating gel developed by researchers at the University of Colorado Boulder could dramatically increase the energy efficiency of skyscrapers and other buildings, and might one day help scientists to build greenhouse-like habitats for colonists on Mars. The “aerogel,” which looks like a flattened plastic contact lens, is so resistant to heat that you could put a strip of it on your hand and light a fire on top without feeling a thing. But unlike similar products on the market, the material is mostly see-through (Nano Energy, „Flexible transparent aerogels as window retrofitting films and optical elements with tunable birefringence”).
“Transparency is an enabling feature because you can use this gel in windows, and you could use it in extraterrestrial habitats,” said Ivan Smalyukh, a professor in the Department of Physics. “You could harvest sunlight through that thermally insulating material and store the energy inside, protecting yourself from those big oscillations in temperature that you have on Mars or on the moon.”
The group’s gel is also cheaper to produce because it comes from humble beginnings: beer waste.
Aerogels are at least 90 percent gas by weight, Smalyukh explained, but their defining feature is air. Their thin films are made up of crisscrossing patterns of solid material that trap air inside billions of tiny pores, similar to the bubbles in bubble wrap. It’s that trapping capacity that makes them such good insulators.
“You create a very tortuous network of these nanoparticles that link together in the aerogel, preventing the heat from going through,” Smalyukh said.
Most currently available aerogels, however, are opaque—a big problem if you want to use them to coat windows.
To make a different type of gel, Smalyukh and his colleagues begin with the common plant sugar cellulose. By carefully controlling how cellulose molecules link up, the team is able to orient them into a lattice-like pattern. That pattern is so uniform, he said, that it allows light to pass through unbothered, giving the gel its transparent appearance.
Researchers can make cellulose by adding specialized bacteria to a wide range of food waste. The team has been driving to breweries across the Boulder area to collect tubs of beer wort, or the waste liquid produced during the brewing process.
“So not only are we recycling and saving this valuable material from entering the landfill, but we’re also producing this raw material cheaply,” said Andrew Hess, a Ph.D. student in physics at CU Boulder.
The final product of the team’s efforts is a thin, flexible film that is roughly 100 times lighter than glass.
That could be especially useful for buildings in the United States. According to the Department of Energy, roughly one-quarter of the energy that is expended to heat and cool buildings in the country goes toward offsetting the loss of heat through windows, potentially costing building operators billions of dollars per year.
“We’re envisioning a retrofitting product that would basically be a peel-and-stick film that a consumer would buy at Home Depot,” Hess said.
Smalyukh and his colleagues have been exploring partnerships with window manufacturing companies and earlier this summer, their project was named one of the winners of NASA’s 2018 iTech competition. This national contest seeks out Earth-bound technologies that might one day help people travel to space.
“Our approach so far has been around windows,” Hess said. “However, we also see our technology being enabling for so many other applications, including smart clothes, for insulating cars and protecting firefighters.”
Source: By Daniel Strain, University of Colorado Boulder
chimiștii au demonstrat că trei structuri de carbon create recent de către oamenii de știință din Coreea de Sud și Japonia sunt, de fapt, schwarzi-urile căutate de mult timp, pe care cercetătorii le prezică că vor avea proprietăți electrice unice și de stocare cum ar fi cele descoperite acum în buckminsterfullerenes sau fullerene pentru scurt), nanotuburi și grafen.
Noile structuri au fost construite în interiorul porilor de zeoliți, forme cristaline de dioxid de siliciu – nisip – utilizat mai frecvent ca dedurizatori de apă în detergenții de rufe și pentru a crăpa catalitic petrolul în benzină. Denumit carbonul zeolit-template (ZTC), structurile au fost investigate pentru posibile proprietăți interesante, deși creatorii nu au fost conștienți de identitatea lor ca schwarzites, pe care chimistii teoretici au lucrat timp de decenii.
Posted: Aug 13, 2018
Long-sought carbon structure ‘schwarzite’ joins graphene, fullerene family
(Nanowerk News) The discovery of buckyballs surprised and delighted chemists in the 1980s, nanotubes jazzed physicists in the 1990s, and graphene charged up materials scientists in the 2000s, but one nanoscale carbon structure – a negatively curved surface called a schwarzite – has eluded everyone. Until now.
University of California, Berkeley, chemists have proved that three carbon structures recently created by scientists in South Korea and Japan are in fact the long-sought schwarzites, which researchers predict will have unique electrical and storage properties like those now being discovered in buckminsterfullerenes (buckyballs or fullerenes for short), nanotubes and graphene.
The new structures were built inside the pores of zeolites, crystalline forms of silicon dioxide – sand – more commonly used as water softeners in laundry detergents and to catalytically crack petroleum into gasoline. Called zeolite-templated carbons (ZTC), the structures were being investigated for possible interesting properties, though the creators were unaware of their identity as schwarzites, which theoretical chemists have worked on for decades.
Carbon atoms (black) assembling on the molecular surface of a zeolite (red oxygen atoms and yellow silicon atoms) to form a negatively curved schwarzite. (Graphics by Yongjin Lee and Efrem Braun)
Based on this theoretical work, chemists predict that schwarzites will have unique electronic, magnetic and optical properties that would make them useful as supercapacitors, battery electrodes and catalysts, and with large internal spaces ideal for gas storage and separation.
UC Berkeley postdoctoral fellow Efrem Braun and his colleagues identified these ZTC materials as schwarzites based of their negative curvature, and developed a way to predict which zeolites can be used to make schwarzites and which can’t.
“We now have the recipe for how to make these structures, which is important because, if we can make them, we can explore their behavior, which we are working hard to do now,” said Berend Smit, an adjunct professor of chemical and biomolecular engineering at UC Berkeley and an expert on porous materials such as zeolites and metal-organic frameworks.
Smit, the paper’s corresponding author, Braun and their colleagues in Switzerland, China, Germany, Italy and Russia will report their discovery this week in the journal Proceedings of the National Academy of Sciences („Generating carbon schwarzites via zeolite-templating „). Smit is also a faculty scientist at Lawrence Berkeley National Laboratory.
Playing with carbon
Diamond and graphite are well-known three-dimensional crystalline arrangements of pure carbon, but carbon atoms can also form two-dimensional “crystals” — hexagonal arrangements patterned like chicken wire. Graphene is one such arrangement: a flat sheet of carbon atoms that is not only the strongest material on Earth, but also has a high electrical conductivity that makes it a promising component of electronic devices.
The cage structure of a schwarzite that was formed inside the pores of a zeolite. The zeolite is subsequently dissolved to release the new material. (Image: Yongjin Lee and Efrem Braun)
Graphene sheets can be wadded up to form soccer ball-shaped fullerenes – spherical carbon cages that can store molecules and are being used today to deliver drugs and genes into the body. Rolling graphene into a cylinder yields fullerenes called nanotubes, which are being explored today as highly conductive wires in electronics and storage vessels for gases like hydrogen and carbon dioxide. All of these are submicroscopic, 10,000 times smaller than the width of a human hair.
To date, however, only positively curved fullerenes and graphene, which has zero curvature, have been synthesized, feats rewarded by Nobel Prizes in 1996 and 2010, respectively.
In the 1880s, German physicist Hermann Schwarz investigated negatively curved structures that resemble soap-bubble surfaces, and when theoretical work on carbon cage molecules ramped up in the 1990s, Schwarz’s name became attached to the hypothetical negatively curved carbon sheets.
“The experimental validation of schwarzites thus completes the triumvirate of possible curvatures to graphene; positively curved, flat, and now negatively curved,” Braun added.
Minimize me
Like soap bubbles on wire frames, schwarzites are topologically minimal surfaces. When made inside a zeolite, a vapor of carbon-containing molecules is injected, allowing the carbon to assemble into a two-dimensional graphene-like sheet lining the walls of the pores in the zeolite. The surface is stretched tautly to minimize its area, which makes all the surfaces curve negatively, like a saddle. The zeolite is then dissolved, leaving behind the schwarzite.
A computer-rendered negatively curved soap bubble that exhibits the geometry of a carbon schwarzite. (Image: Felix Knöppel)
“These negatively-curved carbons have been very hard to synthesize on their own, but it turns out that you can grow the carbon film catalytically at the surface of a zeolite,” Braun said. “But the schwarzites synthesized to date have been made by choosing zeolite templates through trial and error. We provide very simple instructions you can follow to rationally make schwarzites and we show that, by choosing the right zeolite, you can tune schwarzites to optimize the properties you want.”
Researchers should be able to pack unusually large amounts of electrical charge into schwarzites, which would make them better capacitors than conventional ones used today in electronics. Their large interior volume would also allow storage of atoms and molecules, which is also being explored with fullerenes and nanotubes. And their large surface area, equivalent to the surface areas of the zeolites they’re grown in, could make them as versatile as zeolites for catalyzing reactions in the petroleum and natural gas industries.
Braun modeled ZTC structures computationally using the known structures of zeolites, and worked with topological mathematician Senja Barthel of the École Polytechnique Fédérale de Lausanne in Sion, Switzerland, to determine which of the minimal surfaces the structures resembled.
The team determined that, of the approximately 200 zeolites created to date, only 15 can be used as a template to make schwarzites, and only three of them have been used to date to produce schwarzite ZTCs. Over a million zeolite structures have been predicted, however, so there could be many more possible schwarzite carbon structures made using the zeolite-templating method.
Universitatea din Texas de la Arlington a brevetat o piele inteligenta, creata de un cercetator UTA, care va da robotilor senzatii tactile mai sensibile decat oameni.Pielea inteligenta este de fapt alcatuita din milioane de senzori de nanofire flexibile care au mult mai multe informatii decat pielea oamenilor. Pe măsură ce senzorii perie o suprafață, robotul colectează toate informațiile pe care senzorii le trimit înapoi.Alte aplicații posibile viitoare includ aderarea pielii inteligente la proteze pentru a le dota cu un sentiment, aplicarea tehnologiei pe alte dispozitive medicale, țeserea pielii în uniforma unui soldat de luptă, astfel încât să poată fi detectată orice substanță chimică toxică sau identificarea amprentelor digitale.
Posted: Aug 09, 2018
Flexible nanowire sensors give robots ultra-sensitive skin
(Nanowerk News) The University of Texas at Arlington has patented a smart skin, created by a UTA researcher, that will give robots more sensitive tactile feeling than humans.
“The idea is to have robots work better alongside people,” said Zeynep Çelik-Butler, a UTA electrical engineering professor. “The smart skin is actually made up of millions of flexible nanowire sensors that take in so much more information than people’s skin. As the sensors brush against a surface, the robot collects all the information those sensors send back.”
Çelik-Butler said the sensors, which are flexible and made of zinc oxide nanorods, are self-powered and do not need any external voltage for operation. Each is about 0.2 microns in diameter, while a human hair is about 40 to 50 microns.
In addition, the developed sensors were fully packaged in a chemical and moisture resistant polyimide that greatly enhances usability in harsh environments. The result is a thin, flexible, self-powered tactile sensing layer, suitable as a robotic or prosthetic skin.
Smart skin technology. (Image: UTA)
The smart skin technology allows the robots to sense temperature changes and surface variations, which would allow a person alongside the robot to be safer or react accordingly.
Other possible future applications include adhering the smart skin to prosthetics to equip them with some feeling, applying the technology to other medical devices, weaving the skin into the uniform of a combat soldier so that any toxic chemicals could be detected or fingerprint identification.
“These sensors are highly sensitive and if they were brushed over a partial fingerprint, the technology could help identify who that person is,” Çelik-Butler said. “Imagine people being able to ascertain a person’s identity with this hairy robot, as my students call it.”
Teri Schultz, director of technology management in the UTA Office of Research, said the technology shows promise in a number of commercial sectors.
“Robots are the here and now,” Schultz said. “We could see this technology develop with the next generation of robots to allow them to be more productive in helping people.”
Un material care constă în atomi dintr-un singur element, dar are proprietăți complet diferite în funcție de aranjamentul atomic – acest lucru poate părea ciudat, dar este de fapt realitate cu nano-panglici graphene. Panglicile, care au doar câțiva atomi de carbon și un singur atom gros, au proprietăți electronice foarte diferite, în funcție de forma și lățimea lor: conductor, semiconductor sau izolator.
Posted: Aug 09, 2018
Quantum chains in graphene nanoribbons
(Nanowerk News) Empa researchers, together with researchers from the Max Planck Institute for Polymer Research in Mainz and other partners, have achieved a breakthrough that could in future be used for precise nanotransistors or – in the distant future – possibly even quantum computers, as the team reports in the current issue of the scientific journal Nature („Engineering of robust topological quantum phases in graphene nanoribbons”).
When graphene nanoribbons contain sections of varying width, very robust new quantum states can be created in the transition zone.
A material that consists of atoms of a single element, but has completely different properties depending on the atomic arrangement – this may sound strange, but is actually reality with graphene nano-ribbons. The ribbons, which are only a few carbon atoms wide and exactly one atom thick, have very different electronic properties depending on their shape and width: conductor, semiconductor or insulator.
An international research team led by Empa’s „nanotech@surfaces” laboratory has now suc-ceeded in precisely adjusting the properties of the ribbons by specifically varying their shape. The particular feature of this technology is that not only can the „usual” electronic properties mentioned above be varied – it can also be used to generate specific local quantum states.
So what’s behind it? If the width of a narrow graphene nanoribbon changes, in this case from seven to nine atoms, a special zone is created at the transition: because the electronic properties of the two areas differ in a special, so-called topological way, a „protected” and thus very robust new quantum state is created in the transition zone. This local electronic quantum state can now be used as a basic component to produce tailor-made semiconductors, metals or insulators – and possibly even as a component in quantum computers.
The Empa researchers under the lead of Oliver Gröning were able to show that if these ribbons are built with regularly alternating zones of different widths, a chain of interlinked quantum states with its own electronic structure is created by the numerous transitions. The exciting thing is that the electronic properties of the chain change depending on the width of the different segments. This allows them to be finely adjusted – from conductors to semiconductors with different bandgaps. This principle can be applied to many different types of transition zones – for example, from seven to eleven atoms.
„The importance of this development is also underlined by the fact that a research group at the University of California, Berkeley, came to similar results independently of us,” said Gröning. The work of the US research team has been published in the same issue of Nature .
On the way to nanoelectronics
Based on these novel quantum chains, precise nano-transistors could be manufactured in the future – a fundamental step on the way to nanoelectronics. Whether the switching distance between the „1” state and the „0” state of the nanotransistor is actually large enough depends on the bandgap of the semiconductor – and with the new method this can be set almost at will.
The electronic properties of the chain can be finely adjusted.
In reality, however, this is not quite as simple: for the chain to have the desired electronic properties, each of the several hundred or even thousands of atoms must be in the right place.
„This is based on complex, interdisciplinary research, ” says Empa researcher Gröning. „Researchers from different disciplines in Dübendorf, Mainz, Dresden, and Troy (USA) worked together – from theoretical understanding and specific knowledge of how precursor molecules have to be built and how structures on surfaces can be selectively grown to structural and electronic analysis using a scanning tunneling microscope.”
An excursion into the quantum realm
Ultrasmall transistors – and thus the next step in the further miniaturization of electronic circuits – are the obvious application possibilities here: although they are technically challenging, electronics based on nanotransistors actually work fundamentally the same as today’s microelectronics.
The semiconducting nanoribbons produced by the Empa researchers would allow transistors with a channel cross-section 1,000 times smaller than typically manufactured today. However, further possibilities can also be imagined, for example in the field of spintronics or even quantum informatics.
Top: Schematic representation of the production of hybrid nanobands using two different precursor molecules. The left (small) produces a smooth 7-carbon atom wide nanoband. The larger one produces a 7-11 atom wide, caroform segment. Atomic force microscopy: Atomic force microscope image of a hybrid graphene nanoband with 5 „diamond” segments (7-11 segments) in the middle which is continued left and right by smooth 7-nanobands. The black scale bar is 1 nm long. Scanning tunnel spectroscopy: Spectroscopic image of the localized quantum states (bright regions) at both ends of the diamond region. The section corresponds to that of the atomic force microscope image. Simulation of the scanning tunnel spectroscopy: Theoretical prediction of how the quantum states to be expected at the end of the diamond segment should look in the experiment.
This is because the electronic quantum states at junctions of graphene nanoribbons of different widths can also carry a magnetic moment. This could make it possible to process information not by charge as was previously customary, but by the so-called spin – in the figurative sense the „direction of rota-tion” of the state. And the development could even go one step further.
„We have observed that topological end states occur at the ends of certain quantum chains. This offers the possibility of using them as elements of so-called qubits – the complex, interlocked states in a quantum computer,” explains Oliver Gröning.
Today and tomorrow, however, no quantum computer is built from nanoribbons – there is still a lot of research needed, says Gröning: „The possibility of flexibly adjusting the electronic properties through the targeted combination of individual quantum states represents a major leap for us in the production of new materials for ultra-miniaturized transistors.”
The fact that these materials are stable under environmental conditions plays an important role in the development of future applications.
„The further-reaching potential of the chains to create local quantum states and link them together in a targeted manner is also fascinating,” Gröning continues. „Whether this potential can actually be exploited for future quantum computers remains to be seen, however. It is not enough to create localized topological states in the nanoribbons – these would also have to be coupled with other materials such as superconductors in such a way that the conditions for qubits are actually met.”
