Echipa a confirmat natura helicoidală a structurii prin cristalografie cu raze X, găsind și nanografi în sensul acelor de ceasornic și în sens invers acelor de ceasornic. Teste suplimentare au arătat că structura electronică și proprietățile de fotosabsorbție ale acestui compus sunt mult diferite de cele anterioare.
Schenmatic concept of nanographenes. (Image: Osaka University and Kyoto University)
These graphene constructs previously existed only in theory, so successful synthesis offers promising applications from nanoscale induction coils, to molecular springs for use in nanomechanics.
Graphene – a hexagonal lattice of single layer carbon atoms exhibiting outstanding charge and heat transport properties – has garnered extensive research and development interest.
Helically twisted graphenes have a spiral shape. Successful synthesis of this type of graphene could have major applications, but its model compounds have never been reported. And while past research has gotten close, resulting compounds have never exhibited expected properties.
„We processed some basic chemical compounds through step-by-step reactions, such as McMurry coupling, followed by stepwise photocyclodehydrogenation and aromatization,” explains first author Yusuke Nakakuki. „We then found that we had synthesized the foundational backbone of helical graphene.”
Chemical structure of the nanographene synthesized in the present work. (Image: Osaka University and Kyoto University)
The team confirmed the helicoid nature of the structure through X-ray crystallography, also finding both clockwise and counter-clockwise nanographenes. Further tests showed that the electronic structure and photoabsorption properties of this compound are much different from previous ones.
„This helical nanographene is the first of its kind,” concludes lead author Kenji Matsuda. „We will try to expand their surface area and make the helices longer. I expect to find many new physical properties as well.”
au descoperit ca grafenul „holey” ofera o cale in jurul acestei probleme. Ei foloseau coli de grafen dopate cu azot pentru a încapsula un aliaj de electrozi de nichel-molibden (NiMo). Crucial, grafenul a fost perforat plin de găuri de dimensiuni nanometrice, ca un șuviță.
Posted: Apr 26, 2018
Punching holes in graphene to boost hydrogen production
(Nanowerk News) Researchers may have brought the renewable energy future one step closer. A new electrode can accomplish the hydrogen evolution reaction (HER) in acidic conditions, making the technology both cheaper and more effective. The process is helped by a smart form of graphene.
The electrolysis of water to hydrogen is vital for energy storage in a green economy. One of the major obstacles, however, is the high cost of noble-metal electrodes. Cheaper non-nobles do work, but mainly in alkaline conditions, where the reaction is electricity-hungry; the more efficient acid-phase reaction requires scarce commodity metals such as platinum. Worse still, the acid electrolytes are corrosive and eat away at the core metal.
Now, researchers led by the University of Tsukuba have found that “holey” graphene offers a way round this problem. They used nitrogen-doped graphene sheets to encapsulate a nickel–molybdenum (NiMo) electrode alloy. Crucially, the graphene was punched full of nanometer-size holes, like a colander.
Porous NiMo composite covered with holy graphene. (Image: University of Tsukuba)
The use of graphene in HER electrodes is not new – this flexible, conductive carbon sheet is ideal for wrapping around the core metal. However, while protecting the metal against corrosion, graphene also suppresses its chemical activity. In the new Tsukuba system, the all-important holes promote the reaction in two ways, while the intact graphene part protects the metal.
“We created holes by decorating the NiMo surface with silica nanoparticles,” explains study co-author Kailong Hu. “Then, when we deposited the graphene layer, gaps were left behind at the nanoparticle positions – like a relief artwork. In fact, the holes are more than just gaps – they are ringed by chemically active ridges called ‘fringes’. Technically, these fringes are structural defects, but they drive the chemistry of the electrode.”
Compared with normal graphene, the fringes are more hydrophilic. This attracts hydronium (H3O+) in the acid solution, which plays a crucial role in one of the two HER mechanisms. The fringes are also excellent at adsorbing single H atoms, which provides extra surface area for the other important HER process. As a result, H2 is produced as efficiently as on a conventional (but expensive) Pt/C electrode. Meanwhile, the non-holey part of graphene delays the metal catalyst from dissolving in the acid.
“This is a versatile new concept for hydrogen evolution electrodes,” lead author Yoshikazu Ito says. “The goal is to minimize the overpotential needed for the reaction. Therefore, it’s not limited to one particular catalyst. We tuned our holey graphene layer specifically to NiMo by optimizing the size and number of holes. What’s impressive is that the catalyst was still stable in acid, despite the holes. In the future, holey graphene could be customized to a range of metals, pushing the efficiency of hydrogen production toward full-scale adoption.”
Haldele perovskite sunt într-o clasă interesantă de materiale pentru optoelectronică și fotovoltaice. Aceste materiale absoarbe eficient lumina vizibila, au lungimi lungi de difuzie si sunt usor si ieftin de realizat. Performanța dispozitivelor optice poate fi, de asemenea, îmbunătățită prin încorporarea particulelor pe scară nanometrică, care au proprietăți de absorbție și absorbție a luminii mult superioare decât materialul în vrac din care sunt derivate. Deci nu este surprinzător faptul că oamenii de știință sunt dornici să combine aceste două abordări. Provocarea este că particulele mici de perovskite nu sunt întotdeauna stabile din punct de vedere chimic, iar structura lor de cristal atomic este dificil de controlat.
Halide perovskites are in an exciting class of materials for optoelectronics and photovoltaics. These materials efficiently absorb visible light, possess long charge-carrier diffusion lengths and are easy and cheap to produce. The performance of optical devices can also be improved by incorporating nanometer-scale particles, which have far superior light-emitting and -absorbing properties than the bulk material from which they are derived. So it is unsurprising that scientists are keen to combine these two approaches. The challenge is that tiny perovskite particles aren’t always chemically stable, and their atomic crystal structure is difficult to control.
Attaching molecules, referred to as ligands, can stabilize a nanocrystal. But this so-called passivation can form an electrically insulating shell around the particle that inhibits their effectiveness in electronic devices.
Passivating the surface of perovskite nanocrystals with IDA molecules improves their stability and their optical and electrical properties, making them useful for optoelectronic devices. (Image: KAUST)
Now, Osman Bakr’s group, and co-workers from KAUST and ShanghaiTech University, has created halide perovskite nanocrystals made from cesium-lead-iodide passivated by 2,2′-iminodibenzoic acid (IDA) ligands. They show that this provides the necessary chemical stability while remaining useful for optoelectronics. And the passivation was simple: just adding IDA powder into the nanocrystal solution and using a centrifuge to remove any excess.
The team chose IDA because it is a bidentate ligand, meaning that it bonds to the nanocrystal at two sites. “The conventional ligands used in these applications, such as oleic acid, are dynamic on the surface of the perovskite nanocrystals and easily come loose,” says Jun Pan, the first author on the paper. “That’s why we apply a double carboxylic group to strongly bind on the surface, which also stabilizes the perovskite crystal phase at room temperature.”
Pan and his team compared the optical properties of both the passivated and unpassivated samples and observed that the treatment improved the photoluminescent quantum yield—a measure of how many photons are emitted for every photon absorbed—from 80 percent to over 95 percent. And while the intensity of light emitted from the unpassivated nanocrystals had dropped significantly five days later, the IDA-treated samples were still emitting light at 90 percent of their initial level 15 days later.
The team demonstrated that their stabilized halide perovskite nanocrystals were suitable for optoelectronic applications by using them to build light-emitting diodes. The red-light generating devices again outperformed the unpassivated control device in terms of maximum luminance and luminous power efficiency.
“The next step is to realize more stable perovskite structures and to create an LED with performance above 10 percent based on perovskite nanocrystals,” says Pan.
Source: King Abdullah University of Science and Technology (KAUST)
Grafenul are multe proprietăți; este, de exemplu, un conductor extrem de bun. Dar nu absorb foarte bine lumina. Pentru a remedia acest aspect limitativ al materialului altfel uimitor, fizicienii recurg la înglobarea unei foi de grafen într-un cristal fotonic plat, care este excelent pentru controlul fluxului de lumină. Combinația oferă grafen cu capacități de absorbție a luminii substanțial îmbunătățite.Acest lucru arată că există un număr de caracteristici care pot fi reglate care pot fi exploatate pentru proiectarea nano-dispozitivelor bazate pe grafen, cum ar fi absorbanții și senzorii sensibili la temperatură.
Posted: Apr 25, 2018
Turning graphene into light nanosensors
(Nanowerk News) Graphene has many properties; it is e.g. an extremely good conductor. But it does not absorb light very well. To remedy this limiting aspect of what is an otherwise amazing material, physicists resort to embedding a sheet of graphene in a flat photonic crystal, which is excellent for controlling the flow of light. The combination endows graphene with substantially enhanced light-absorbing capabilities.
In a new study published in EPJ B („Tunability of temperature-dependent absorption in a graphene-based hybrid nanostructure cavity”), Arezou Rashidi and Abdolrahman Namdar from the University of Tabriz, Iran demonstrate that, by altering the temperature in such a hybrid cavity structure, they can tune its capacity for optical absorption. They explain that it is the thermal expansion and thermo-optical effects which give the graphene these optical characteristics. Potential applications include light sensors, ultra-fast lasers, and systems capable of modulating incoming optical beams.
The authors study the light absorption of the material as a function of temperature, the chemical energy potential, the light polarisation and its incidence angles. To do so, they use a modelling method called the transfer matrix method. They find that for normal light incidence, there is enhanced absorption at room temperature, while the absorption peak is shifted toward the red as the temperature increases.
As light comes in at an angle, the authors show that the absorption peaks are sensitive to the incident angles as well as the polarisation state of the light. They also find that by increasing the incident angle, the peak wavelength is shifted toward the blue.
They conclude that the peak wavelength can be controlled by varying either the temperature or incident angle, as well as the chemical energy potential of graphene. This shows that there are a number of tunable features that could be exploited for the design of graphene-based nano-devices, such as temperature-sensitive absorbers and sensors.
au dezvoltat un nanofibru polimer puternic, ușor, conductiv termic, izolator electric și biocompatibil.Caracteristicile nanofibrelor sale polimerice îi conferă aplicabilitate în sistemele aerospațiale și auto, inginerie civilă și structurală, dispozitive medicale și robotică.
Posted: Apr 25, 2018
A high-tech spin on spider silk
(Nanowerk News) Spiderman has it figured out.
It’s no coincidence then that when Sheng Shen talks about his work with polymer nanofibers he compares it to a spider spinning its web.
“Just as a spider synthesizes silk from protein polymer to form a fiber with strength similar to high tensile steel, polymers can be spun and drawn to form high-strength materials with exceptionally high thermal conductivity,” said Shen, associate professor of mechanical engineering at Carnegie Mellon University.
Shen and his team have developed a polymer nanofiber that is strong, lightweight, thermally conductive, electrically insulating, and bio-compatible. They accomplished all of this in a single polymer fiber strand measuring less than 100 nanometers (Nature Communications, „Crystalline polymer nanofibers with ultra-high strength and thermal conductivity”).
According to Shen, the potential impact of this development is tremendous. The characteristics of his polymer nanofiber give it application in aerospace and automotive systems, civil and structural engineering, medical devices, and robotics.
Mechanical Engineering faculty member Sheng Shen describes his work developing low-density, multi-functional materials that have a broad range of applications in aerospace, automotive, and biomedical technologies.
In their simplest form, polymers are lots of identical molecules joined together over and over. The molecules could be joined in “simple” chains or more complicated structures. Either way, the resulting polymer has the same characteristics as the molecules used to create it. This means a polymer could be sticky, solid, pliable, or any number of other physical characteristics contained in its molecules.
Traditionally, said Shen, polymers are “the general material platform (used) to develop multifunctional materials,” including plastics, nylons, and rubbers. Polymers are easily processed at relatively low price points, but do have their drawbacks.
Prototypical bulk polymers are often amorphous, meaning their molecule chains are randomly coiled and lacking a defined shape and form. This lack of definition can lead to reduced strength, reduced thermal conductivity, and increased defects like voids and molecule entanglements.
The challenge was to develop a polymer that is both ultra-strong and thermally conductive.
For Shen, the place to do this was at the nano-level. At this level—one-billionth of one meter— Shen can engineer individual molecules to join together in exactly the way he wants them to join together.
“At the nanoscale, the polymer chains become highly oriented and defects that lower strength and thermal conductivity can be eliminated,” Shen said.
The resulting polymer nanofiber has a Young’s Modulus (the measure of the stiffness of a solid material) and a strength that Shen said are 300-times greater than bulk polymers.
As for thermal conductivity, Shen reports that his polymer nanofiber measures a conductivity rate of 100 W/mK. On average, the conductivity rate of steel is 54 W/mK and the rate of iron is 73 W/mK.
“These nanofibers provide a low-cost route to achieving highly effective heat removal in electronic systems,” said Shen. “They can also be bio-compatible heat spreaders for improving patient care.”
To date, Shen and his team have tested single nanofibers. On the strength of the results from those tests, they have turned their attention to creating an innovative manufacturing approach that will allow for the mass production of the polymer nanofibers.
Shen is confident that he and his team have invented a product that will have practical and large-scale impacts sooner rather than later.
“We really believe this is a game-changing technology by transforming polymers from soft and thermally insulating materials to ultra-strong and thermally conductive material,” Shen said.
au dezvoltat o nouă abordare tehnologică care a generat nanoparticule de argint De 32 de ori capacitatea bactericidă a celor utilizate în prezent în ambalarea produselor alimentare, ortezi, spitale și materiale medicale, printre altele.Aceste nanocompozite au fost compuse din nanoparticule de argint cuplate la un cristal semiconductor de tungsten de argint prin microscopie electronică de transmisie.
Posted: Apr 25, 2018
Novel technique achieves 32-fold increase in bactericidal effects of nanosilver
(Nanowerk News) In recent decades, various research groups in the field of materials science have invested time and resources to answer the following question: is it possible to develop new techniques capable of producing silver particles on a nanometric scale, thus enhancing the optical, catalytic and bactericidal properties of silver? A group of Brazilian investigators has taken a step forward in this contest.
In a research carried out within the Center for Development of Functional Materials (CDMF), one of the Research, Innovation & Dissemination Centers (RIDCs) funded by the São Paulo Research Foundation – FAPESP, they developed a new technological approach that generated silver nanoparticles with 32 times the bactericidal capacity of those currently used in food packaging, orthotics, and hospital and medical materials, among others.
A Professor at UFSCar and executive director for the CDMF, Elson Longo says that CDMF’s researchers developed an innovative method of obtaining nanocomposites three years ago. These nanocomposites were comprised of silver nanoparticles coupled to a silver tungstate semiconductor crystal by transmission electron microscopy.
However, the high cost of transmission electron microscopes limited plans of large-scale production of these materials for real-world applications. „The transmission electron microscope used to obtain this material costs approximately 1.3 million euros,” Longo said. The technique involved electron-beam irradiation of silver tungstate, which resulted in promising bactericides whereby the silver tungstate semiconductor attracts bacterial agents that are then are neutralized by silver nanoparticles.
To scale up production of these nanocomposites using a more competitive method, the researchers developed a novel technique consisting of pulsed laser irradiation of a silver tungstate semiconductor, with each pulse lasting only a femtosecond – one millionth of one billionth of a second (10-15 s).
Analysis of the irradiated samples showed that interaction between the silver tungstate semiconductor and the femtosecond laser gave rise to large numbers of microstructures, which they characterized by transmission electron microscopy and found to be of two different types.
„The new technique we developed resulted both in silver nanoparticles left on the semiconductor and in silver clusters,” said the coordinator of the FAPESP-funded research center.
To measure the bactericidal activity of the materials, the researchers placed samples of them in contact with methicillin-resistant strains of Staphylococcus aureus (MRSA), a bacterium that is resistant to numerous antibiotics and is frequently at the root of hospital-acquired infections.
Microscopic analysis showed a 32-fold increase in bactericidal activity for the laser-irradiated samples compared with silver nanoparticles produced by electron-beam irradiation.
„The new technique offers the possibility of obtaining high-performance bactericidal compounds that are easy to produce,” Longo said.
Potential applications
The researchers have applied for a patent on the new technique and the two new classes of silver nanoparticle obtained by the technique.
The idea is to license the technology to Nanox, a spinoff from CDMF based in São Carlos, São Paulo State, and supported by FAPESP’s Innovative Research in Small Business Program (PIPE http://www.bv.fapesp.br/en/3).
„Nanox already sells silver nanoparticles worldwide and could benefit a great deal from the new technique for obtaining the material,” Longo said.
The researchers plan to evaluate use of the material in dental prosthetics and have begun trials to investigate the action of nanocomposites in cancer cells.
Preliminary results of the experiments suggest the nanoparticles can eliminate tumor cells without affecting healthy cells.
Source: Fundação de Amparo à Pesquisa do Estado de São Paulo
În cursul studiului, echipa sa concentrat pe materiale semiconductoare 2D. Printre altele, acestea includ grafen, fosfor, straturi 2D de disulfură de molibden și perovskite 2D care au atras recent atenția oamenilor de știință. Aceste materiale sunt cristale de un atom gros cu proprietăți electronice 2D. Cercetătorii cred că pot fi utilizați pentru dezvoltarea de noi dispozitive.
Posted: Apr 24, 2018
2D sheets of cadmium telluride can spontaneously fold into nanoscrolls
(Nanowerk News) A team of scientists from the Faculty of Chemistry and the Faculty of Materials Science, MSU together with foreign colleagues discovered that two-dimensional sheets of cadmium telluride can spontaneously fold into nanoscrolls. This effect may be used in electronics and photonics. The results of the study were published in Chemistry of Materials („Spontaneous Folding of CdTe Nanosheets Induced by Ligand Exchange”).
In the course of the study the team focused on 2D semiconductor materials. Among others, they include graphene, phosphorene, 2D layers of molybdenum disulfide, and 2D perovskites that have recently attracted lots of attention from scientists. These materials are one atom thick crystals with 2D electronic properties. Researchers believe that they may be used for the development of new devices.
These are TEM images of 2-D cadmium telluride sheets. Left: initial flat sheets. Right: sheets after folding. Upper right corner: a scheme of a folded sheet. (Image: Roman Vasiliev)
„We studied 2D cadmium telluride CdTe and discovered an unexpected effect of spontaneous folding of its ultrathin (only 1 nm) sheets that are also called colloidal quantum wells,” said Roman Vasiliev, a co-author of the work, PhD of Chemical Sciences, and Associate Professor of the Faculty of Chemistry and the Faculty of Materials Science, MSU.
Colloidal quantum wells are a new generation of colloidal quantum dots. Quantum dots are distinguished by their luminescent properties and are used in commercial devices, such as TV sets. Quantum wells, a 2D type of quantum dots, are being studied today, but we already know that they possess very narrow luminescence bands, which is important for bright color rendering in light-emitting devices.
The team studied the properties of 2D sheets of cadmium telluride by exchanging organic molecules attached to their surface and securing the stability of nanoparticles. In order to synthesize 2D cadmium telluride the scientists used the colloidal method and obtained them in a flask. To do so, the scientists initiated a reaction of obtaining cadmium telluride nanoparticles in an organic solvent in the presence of surfactants. By changing the conditions of the reaction they managed to cause the particles to grow into one nanometer thick sheets.
At first the authors of the work grew flat 2D sheets covered with oleic acid as a stabilizer. They managed to obtain sheets with length reaching hundreds of nanometers and thickness of strictly one nanometer. After that the team started replacing the molecules of oleic acid with other organic molecules and analyzing sizes and shapes of the obtained nanoparticles, as well as their composition and crystal structure. At this stage they used a transmission electron microscope of MSU Shared Knowledge Center.
In the course of the study the team discovered that when a specific type of stabilizers (thiols) is used, flat sheets of cadmium telluride suddenly fold into perfect scrolls. When attached to the surface of a sheet, thiol molecules increase its thickness by one monolayer (0.15 nm) and cause mechanical stresses making the sheet to fold in a certain crystallographic direction. The folding takes place for all nanoparticles at once, and the radius of the fold is the same for all nanostructures.
„The study opens new prospects for manipulations with 2D materials and nanoparticles. The folding effect came as a surprise for us. It resembles the process of making origami, but in this case the sheets are one nanometer thick. Knowing how to change spatial shape of nanoparticles, we could use them in the manufacturing of optic materials with anisotropic behavior and polarized luminescence. We could create active light-emitting matrices for displays that would reduce energy consumption and increase brightness and intensity of various devices. Perhaps, we could also develop new nano-devices, for example, tube-shaped transistors. These interesting properties may be of use in new generations of light-emitting and sensor devices, as well as in optic and optoelectronic technologies and nanotechnologies,” concluded the scientist.
Un nou beton mai ecologic, mai puternic și mai durabil, care este realizat cu ajutorul grafenului, ar putea revoluționa industria construcțiilor.
Posted: Apr 23, 2018
Nanoengineering concrete with graphene drastically reduces carbon footprint
(Nanowerk News) A new greener, stronger and more durable concrete that is made using graphene could revolutionise the construction industry.
Experts from the University of Exeter have developed a pioneering new technique that uses nanoengineering technology to incorporate graphene into traditional concrete production.
The new composite material, which is more than twice as strong and four times more water resistant than existing concretes, can be used directly by the construction industry on building sites. All of the concrete samples tested are according to British and European standards for construction.
Crucially, the new graphene-reinforced concentre material also drastically reduced the carbon footprint of conventional concrete production methods, making it more sustainable and environmentally friendly.
The new concrete developed using graphene by experts from the University of Exeter (Image: Dimitar Dimov / University of Exeter)
The research team insist the new technique could pave the way for other nanomaterials to be incorporated into concrete, and so further modernise the construction industry worldwide.
Professor Monica Craciun, co-author of the paper and from Exeter’s engineering department, said: „Our cities face a growing pressure from global challenges on pollution, sustainable urbanization and resilience to catastrophic natural events, amongst others.
„This new composite material is an absolute game-changer in terms of reinforcing traditional concrete to meets these needs. Not only is it stronger and more durable, but it is also more resistant to water, making it uniquely suitable for construction in areas which require maintenance work and are difficult to be accessed .
„Yet perhaps more importantly, by including graphene we can reduce the amount of materials required to make concrete by around 50 per cent – leading to a significant reduction of 446kg/tonne of the carbon emissions.
„This unprecedented range of functionalities and properties uncovered are an important step in encouraging a more sustainable, environmentally-friendly construction industry worldwide.”
Previous work on using nanotechnology has concentrated on modifying existing components of cement, one of the main elements of concrete production.
In the innovative new study, the research team has created a new technique that centres on suspending atomically thin graphene in water with high yield and no defects, low cost and compatible with modern, large scale manufacturing requirements.
Dimitar Dimov, the lead author and also from the University of Exeter added: „This ground-breaking research is important as it can be applied to large-scale manufacturing and construction. The industry has to be modernised by incorporating not only off-site manufacturing, but innovative new materials as well.
„Finding greener ways to build is a crucial step forward in reducing carbon emissions around the world and so help protect our environment as much as possible. It is the first step, but a crucial step in the right direction to make a more sustainable construction industry for the future.”
au folosit anterior o textură nano-inginerie bazată pe frunzele fuzzy pentru a elabora sticlă auto-curățată și o plasă care separă petrolul de apă.Pentru a testa auto-curățarea, cercetătorii au pulverizat praf de carbură de siliciu negru pe piele și au măsurat cantitatea de pulbere care ar putea fi spălată de o singură picătură de apă. Pe piele sintetică netratată, apa spăla aproximativ 10% din pulbere, în timp ce pe pielea tratată, 90% din ea a fost spălată.
Posted: Apr 23, 2018
A better fake leather, inspired by plants
(Nanowerk News) If you’ve ever stained your favorite leather-look jacket or had to peel your bare legs from a sticky vinyl car seat in the summer, the solution to your woes just might be found on the surface of a lotus leaf.
Researchers at The Ohio State University have previously used a nano-engineered texture based on the fuzzy leaves to devise self-cleaning glass and a mesh that separates oil from water.
Now, in the journal Colloids and Surfaces A („Fabrication of bioinspired superliquiphobic synthetic leather with self-cleaning and low adhesion”), they report that they found a way to adapt the same nature-inspired coating to plastic-based synthetic leather. Both water and oil roll off the coating, which keeps the leather-like surface from getting sticky up to temperatures of 70 degrees Celsius (158 degrees Fahrenheit).
The coating could make for cleaner, less sticky furniture, automotive interiors, clothing, shoes and handbags—any products for which people use synthetic leather, said Bharat Bhushan, Ohio Eminent Scholar and Howard D. Winbigler Professor of mechanical engineering at Ohio State.
In these images, researchers place a drop of oil on an untreated piece of synthetic leather (top, left to right) and a piece of treated synthetic leather (bottom, left to right). After treatment, the oil rolls off. (Image: Ohio State University)
“Genuine leather has been an important material since the beginning of human history,” Bhushan said. “Today, the market for synthetic leather is growing because it’s less expensive and easier to work with. To our knowledge, this is the first time anyone has managed to fabricate synthetic leather that is not just water resistant, but super-liquiphobic—it repels both water and oil-based liquids.”
Synthetic leather is made from fabric coated with plastic, usually polyurethane (PU) or polyvinyl chloride (PVC). Both PVC and PU can be molded into flat sheets with grooves that give it a leather-like texture. Like genuine leather, synthetic leather is somewhat permeable to liquids. Unlike genuine leather, it gets sticky at high temperatures because heat softens the plastic surface.
Bhushan specializes in biomimetics, the science of creating materials and processes that mimic nature. Much of his work has been inspired by lotus leaves, whose bumpy surfaces naturally repel water.
As in their previous experiments creating water- and oil-repellant surfaces, the researchers tried to create a bumpy texture by spraying a coating of silica nano-particles on the surface of the synthetic leather.
But Bhushan and doctoral student Dev Gurera quickly discovered that the plasticizers in the synthetic leather—that is, the chemicals that give plastic its plasticity—prevented the nano-particles from sticking, especially inside the leather-look grooves. So they cleaned the surface with an ultraviolet light treatment commonly used in computer chip manufacturing.
The result: The nano-particles stuck to the cleaned synthetic leather, creating a bumpy surface. Then the researchers sealed the nano-particles with a silicone resin. The coating was mostly transparent, so the leather-like texture was still visible.
Bhushan and Gurera coated samples of PU and PVC and tested them for water and oil repellency and self-cleaning properties, as well as durability and heat resistance.
They squeezed droplets of oil and water onto the synthetic leather and tested how much the surface would have to be tilted for the droplet to roll off. Water rolled off with a tilt of 2 degrees and oil with a tilt of 4 degrees. Any tilt below 10 degrees is considered super-liquiphobic.
To see how wear affected the coating, the researchers scratched a groove into the surface by dragging a small sapphire bead back and forth over it 100 times. The tilt angle required to get droplets to roll off the scratched surface increased to 7 degrees—still super-liquiphobic—but only when the droplet rolled across (that is, perpendicular to the direction of) the worn-in groove.
When the leather was placed so that the droplet would have to roll inside the worn groove, the required angle for the droplet to roll off increased to 44 degrees. That sounds pretty bad, but it’s still better than the untreated PU and PVC surfaces, which remained coated with water or oil even when they were tilted to 90 degrees.
To test self-cleaning, the researchers sprayed black silicon carbide powder on the leather and measured how much of the powder could be washed away by a single water droplet. On untreated synthetic leather, the water washed away about 10 percent of the powder, while on the treated leather, 90 percent of it was washed away.
And the stickiness? The hottest temperature reported inside a closed car sitting in the sunlight is around 80 degrees Celsius (176 degrees Fahrenheit). At that temperature, the researchers said, the coating can’t maintain its integrity, because the PU or PVC beneath it begins to flow like an extremely viscous fluid. The coating did remain un-sticky up to 70 degrees Celsius (158 degrees Fahrenheit), so it could keep your legs from sticking to a car seat on most hot days.
It won’t prevent a very hot seat from burning you, however—so watch out. At least your favorite “leather” jacket will look and feel the same.
Cercetătorii au descoperit că ar putea utiliza vopsea conductoare pentru a crea electrozi pe suprafața unui perete, permițându-i să acționeze atât ca un touchpad pentru a urmări atingerea utilizatorilor, cât și ca un senzor electromagnetic pentru detectarea și urmărirea dispozitivelor și aparatelor electrice.
Posted: Apr 23, 2018
Paint job transforms walls into sensors, interactive surface (w/video)
(Nanowerk News) Walls are what they are – big, dull dividers. With a few applications of conductive paint and some electronics, however, walls can become smart infrastructure that sense human touch, and detect things like gestures and when appliances are used.
Researchers at Carnegie Mellon University and Disney Research found that they could transform dumb walls into smart walls at relatively low cost – about $20 per square meter –using simple tools and techniques, such as a paint roller.
These new capabilities might enable users to place or move light switches or other controls anywhere on a wall that’s most convenient, or to control videogames by using gestures. By monitoring activity in the room, this system could adjust light levels when a TV is turned on or alert a user in another location when a laundry machine or electric kettle turns off.
„Walls are usually the largest surface area in a room, yet we don’t make much use of them other than to separate spaces, and perhaps hold up pictures and shelves,” said Chris Harrison, assistant professor in CMU’s Human-Computer Interaction Institute (HCII). „As the internet of things and ubiquitous computing become reality, it is tempting to think that walls can become active parts of our living and work environments.”
Yang Zhang, a Ph.D. student in the HCII, will present a research paper („Wall++: Room-Scale Interactive and Context-Aware Sensing”) on this sensing approach, called Wall++, at CHI 2018, the Conference on Human Factors in Computing Systems, April 21-26 in Montreal.
The team presents Wall++, a low-cost sensing approach that allows walls to become a smart infrastructure. Instead of merely separating spaces, walls can now enhance rooms with sensing and interactivity. Our wall treatment and sensing hardware can track users’ touch and gestures, as well as estimate body pose if they are close. By capturing airborne electromagnetic noise, we can also detect what appliances are active and where they are located.
The researchers found that they could use conductive paint to create electrodes across the surface of a wall, enabling it to act both as a touchpad to track users’ touch and an electromagnetic sensor to detect and track electrical devices and appliances.
„Walls are large, so we knew that whatever technique we invented for smart walls would have to be low cost,” Zhang said. He and his colleagues thus dispensed with expensive paints, such as those containing silver, and picked a water-based paint containing nickel.
They also wanted to make it easy to apply the special coating with simple tools and without special skills. Using painter’s tape, they found they could create a cross-hatched pattern on a wall to create a grid of diamonds, which testing showed was the most effective electrode pattern. After applying two coats of conductive paint with a roller, they removed the tape and connected the electrodes. They then finished the wall with a top coat of standard latex paint to improve durability and hide the electrodes.
The electrode wall can operate in two modes – capacitive sensing and electromagnetic (EM) sensing. In capacitive sensing, the wall functions like any other capacitive touchpad: when a person touches the wall, the touch distorts the wall’s electrostatic field at that point. In EM sensing mode, the electrode can detect the distinctive electromagnetic signatures of electrical or electronic devices, enabling the system to identify the devices and their locations.
Similarly, if a person is wearing a device that emits an EM signature, the system can track the location of that person, Zhang said.
Wall++ hasn’t been optimized for energy consumption, Zhang said, but he estimated the wall-sized electrodes consume about as much power as a standard touch screen.
Izolații topologici sunt materiale noi care au fost studiate de mai multe grupuri de cercetare din întreaga lume pentru mai mult de zece ani. Principalul avantaj al acestor materiale este prezența (în anumite condiții de simetrie) a stărilor disipante la limita eșantionului, în timp ce materialul în vrac păstrează proprietățile unui izolator. Având în vedere aceste proprietăți, se speră că izolatoarele topologice pot fi utilizate în sistemele avansate de comunicații și procesare a informațiilor, precum și în calculul cuantic.
Multe proprietăți ale izolatoarelor topologice au fost bine descrise teoretic, unele dintre ele fiind verificate experimental. Proprietățile de bază care necesită încă o verificare cuprinzătoare includ forma curbei de disipare a energiei a stărilor de margine într-un izolator topologic, în funcție de componentele lor quasimoment.
Posted: Apr 20, 2018
Scientists propose new arguments for checking the properties of topological insulators
(Nanowerk News) Topological insulators are new materials that have been studied by many research groups around the world for more than ten years. The main advantage of such materials is the presence (under certain symmetry conditions) of dissipationless states at the sample boundary, while the bulk material retains the properties of an insulator. In view of these properties, it is hoped that topological insulators can be used in advanced communications and information processing systems, as well as in quantum computing.
Many properties of topological insulators have by now been well described theoretically, some of them have been verified experimentally. The basic properties that still require comprehensive verification include the shape of the energy dissipation curve of the edge states in a topological insulator, depending on their quasimomentum components.
The law described by this curve underlies most of the observable and applied properties of the material, therefore it is very important to know its details. If, for example, we make a plot of the dissipation law for the electrons on the surface of the Bi2Te3 class compounds, it will resemble a flower with intricately shaped petals. The shape of the petals will contain information about the symmetry of the dissipation law, which directly affects the physical properties of the electron gas.
Researchers at the UNN Faculty of Physics have long been engaged in the study of topological insulators. Recently, work has been completed on the impact of the dissipation law symmetry for electrons on the Bi2Te3 surface on the observed properties of this material. According to Associate Professor of the Department of Theoretical Physics Denis Khomitsky, researchers were able to show that the shape of the „petals” of the dissipation curve, or rather their symmetry, is a reflection of specific and measurable regularities.
Spectrum of Hamiltonian (1) in zero external fields. (Image: Lobachevsky University)
These regularities include the appearance of new peaks in the absorption spectrum of electromagnetic radiation with different polarization, as well as qualitative differences in the dynamics of the wave packet that are manifested when hexagonal distortion or corrugation of the spectrum is taken into account.
„With the results obtained, we will be able to estimate in our future optical and transport experiments the real contribution of this corrugation, that is, to describe more accurately the details of the „petal” shape of the dissipation law”, Denis Khomitsky notes.
The authors of the article published in the April issue of Journal of Experimental and Theoretical Physics hope that a better understanding of this law will contribute to accelerating the development of practically useful applications and devices based on this class of materials.
