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Interesting facts about plastics and rubber

We come across plastics and rubber everywhere in our daily lives. Discover fascinating stories, surprising facts and interesting background information – from historical developments and well-known products to key figures and innovations in the industry.

Results (423)

  • New materials for extra thin computer chips

    Currently, only a small selection of insulators for extremely small transistors exists: SiO2 (right) is amorphous and has an undefined surface, hBN (middle) is crystalline but it is not a good insulator, CaF2 (left) is crystalline, has a clean surface, and is a very good insulator. Image: TU Wien In order to create more compact electronic devices, new materials are being used - especially 2D-materials, which only consist of a single atomic layer. This, however, is only half the story: Every electronic device consists of multiple materials. So the ultra-thin semiconductors have to be paired with ultra-thin insulators. Scientists in Vienna have now found out how to do this. Ever smaller and ever more compact - this is the direction in which computer chips are developing, driven by industry. This is why so-called 2D materials are considered to be the great hope: they are as thin as a material can possibly be, in extreme cases they consist of only one single layer of atoms. This makes it possible to produce novel electronic components with tiny dimensions, high speed and optimal efficiency. However, there is one problem: electronic components always consist of more than one material. 2D materials can only be used effectively if they can be combined with suitable material systems - such as special insulating crystals. If this is not considered, the advantage that 2D materials are supposed to offer is nullified. A team from the Faculty of Electrical Engineering at the TU Wien (Vienna) is now presenting these findings in the journal Nature Communications. Reaching the End of the Line on the Atomic Scale "The semiconductor industry today uses silicon and silicon oxide," says Prof. Tibor Grasser from the Institute of Microelectronics at the TU Wien. "These are materials with very good electronic properties. For a long time, ever thinner layers of these materials were used to miniaturize electronic components. This worked well for a long time - but at some point we reach a natural limit". When the silicon layer is only a few nanometers thick, so that it only consists of a few atomic layers, then the electronic properties of the material deteriorate very significantly. "The surface of a material behaves differently from the bulk of the material - and if the entire object is practically only made up of surfaces and no longer has a bulk at all, it can have completely different material properties." Therefore, one has to switch to other materials in order to create ultra-thin electronic components. And this is where the so-called 2D materials come into play: they combine excellent electronic properties with minimal thickness. Thin layers need Thin Insulators "As it turns out, however, these 2D materials are only the first half of the story," says Tibor Grasser. "The materials have to be placed on the appropriate substrate, and an insulator layer is also needed on top of it - and this insulator also hast to be extremely thin and of extremely good quality, otherwise you have gained nothing from the 2D materials. It's like driving a Ferrari on muddy ground and wondering why you don't set a speed record." A team at the TU Wien around Tibor Grasser and Yury Illarionov has therefore analysed how to solve this problem. "Silicon dioxide, which is normally used in industry as an insulator, is not suitable in this case," says Tibor Grasser. "It has a very disordered surface and many free, unsaturated bonds that interfere with the electronic properties in the 2D material." It is better to look for a well-ordered structure: The team has already achieved excellent results with special crystals containing fluorine atoms. A transistor prototype with a calcium fluoride insulator has already provided convincing data, and other materials are still being analysed. "New 2D materials are currently being discovered. That's nice, but with our results we want to show that this alone is not enough," says Tibor Grasser. "These new electrically conductive 2D materials must also be combined with new types of insulators. Only then can we really succeed in producing a new generation of efficient and powerful electronic components in miniature format". Reference Illarionov et al., Insulators for 2D nanoelectronics: the gap to bridge, Nature Communications (2020), http://dx.doi.org/10.1038/s41467-020-16640-8

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  • For cleaner air, water, and soil

    Toxic chemicals stand no chance against a nanoshield created by scientists from IPC PAS. Photo made on site of the Front Modlin company. Image: IPC PAS, Grzegorz Krzyzewski The air around us is still getting more and more polluted. No wonder many scientists strive to find a way to purify it. Thanks to the work of an international team led by prof. Juan Carlos Colmenares from the Institute of Physical Chemistry, Polish Academy of Sciences, we are a big step closer to achieve this goal. They found a way to make an efficient reactive adsorbent able to purify the air from various toxic compounds, cheaply, and effectively. "Most important is the material we made at the laboratory," says prof. Colmenares. "It not only adsorbs toxic vapors from the air but also, thanks to its photocatalytic properties, can break them into less toxic elements." Material made by the team consists of two quite cheap and easy to acquire compounds: titanium dioxide and graphite oxide. "We intended to make it widely available," explains the professor, and "environmentally friendly." The innovation here was to use ultrasound to make the two counterparts - one organic and one inorganic - to co-operate. The organic counterpart catches the toxic particles, and the inorganic one destroys them by photocatalysis. Ultrasonic manipulation also significantly widens the active surface and chemical heterogeneity of the new material, allowing for higher detoxification efficiency against the "bad guys" from the air. "Thanks to the ultrasound waves, we get excellent dispersion and the layer of graphite oxide sort of rests on the surface of titanium dioxide," says prof. Colmenares. Initially, researchers planned to incorporate this material as an additional filter layer for soldiers' gas masks, or into fabrics, making uniforms that would protect a soldier from toxic gaseous chemicals on the combat field. All this, providing the day, was sunny, and garment had additional LED lights activating photocatalysis. However, high absorptance can be achieved even in the dark. However, although the invention has been tested on warfare agents, its potential applications are much broader and more peaceful. One could, for example, make industrial suits for workers exposed to toxic vapors daily. "Just milligrams in a suit would be sufficient," says professor, "if only dispersed properly. The only downside is that potential fabrics should be artificial polymers rather than natural cotton or flax," he smiles lightly. Scientists would also have to find a way to fasten their nanomaterial to the carrier fabric more securely as clothes get washed. We know that nearly 35% of microplastic found in the environment comes from synthetic clothes and washed linen. "We would not like our nanomaterial to end in rivers and seas," says the professor. "We aim for being environmentally friendly all the way, not only at the level of destroying air toxins." Although, as shown earlier by Dimitrios A. Giannakoudakis, the first author of the current work published in the Chemical Engineering Journal and other members of the international team, by ultrasonication, the active phases can be anchored quickly and stably both on cotton and carbon textiles. If adequately modified, the same technology could help purify not only air but also water and soil. "We have not examined these possibilities yet," says prof. Colmenares, "but it mainly depends on whether we would safely deposit our nanomaterial on possible future carriers/substrates. While purifying water from toxins, we would not like to pollute it with these oxides; we would not want nanotoxicity, although in theory neither TiO2 nor graphite oxide is toxic to humans," explains the scientist. "After all, who was not chewing on a pencil while at school?" If we resolved this issue, we could say, "sky is the limit." New material could detoxify sewage in paper and coke industries or even neutralize highly toxic remnants of World War II, lying deep in the Baltic Sea. "For now, we aim at sewage plants," says the professor. "Photocatalysis and nanocomposites can help where microbes cannot because the environment is too toxic for them." Photocatalysis of the soil is the greatest challenge. However, even this is imaginable with proper mixing, lighting, and a proper photocatalyst, for example, to remove herbicides or pesticides. Cleaner air is within active reach. For cleaner water and soil, we would have to wait a little longer for an optimum solution, but scientists from IPC PAN are just starting their quest for a better, cleaner environment by sustainable approaches for us all. Reference Ginannakoudakis et al., Ultrasound-activated TiO2/GO-based bifunctional photoreactive adsorbents for detoxification of chemical warfare agent surrogate vapors, Chemical Engineering Journal 395 (2020), https://doi.org/10.1016/j.cej.2020.125099

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  • New biomaterial could shield against harmful radiation

    Human cells treated with selenomelanin nanoparticles. Image: Northwestern University Northwestern University researchers have synthesized a new form of melanin enriched with selenium. Called selenomelanin, this new biomaterial shows extraordinary promise as a shield for human tissue against harmful radiation. Packing for outer space? Here's one thing you won't want to forget. Northwestern University researchers have synthesized a new form of melanin enriched with selenium. Called selenomelanin, this new biomaterial shows extraordinary promise as a shield for human tissue against harmful radiation. "Given the increased interest in space travel, and the general need for lightweight, multifunctional and radioprotective biomaterials, we've become excited about the potential of melanin," said Northwestern's Nathan Gianneschi, who led the research. "It occurred to our postdoctoral fellow Wei Cao that melanin containing selenium would offer better protection than other forms of melanin. That brought up the intriguing possibility that this as-yet undiscovered melanin may very well exist in nature, being used in this way. So we skipped the discovery part and decided to make it ourselves." The research will be published online on Wednesday, July 8 in the Journal of the American Chemical Society, ahead of publication in the July print edition. Gianneschi is the Jacob and Rosalind Cohn Professor of Chemistry in Northwestern's Weinberg College of Arts and Sciences and associate director of the International Institute for Nanotechnology. Cao is the paper's first author. Melanin is found in most organisms across the plant and animal kingdoms, as well as in bacteria and fungi. Though best known for pigmentation, melanin also provides valuable protection from radiation. Five kinds of melanin have been observed in nature, with pheomelanin (the pigment in red hair) shown to absorb X-rays more efficiently than the more common eumelanin (black and brown pigments in dark hair). Unwanted exposure to radiation occurs during many common activities, from air travel to X-ray diagnosis and clinical radiation therapy. It's an even greater consideration in extreme cases like a nuclear reactor malfunction or human space travel. NASA's landmark "Twins Study" showed damage to astronaut Scott Kelly's DNA from his year in orbit. An astronaut on a Mars mission could receive up to 700 times more radiation than on Earth. Compared to the weight and bulk of traditional radioprotective materials like lead, melanin it is lighter and more flexible in how it can be used. Melanin samples are currently in orbit at the International Space Station, being studied by another research team for the material's response to radiation exposure. Recent studies have focused on pheomelanin, which contains sulfur, as the best candidate for that purpose. Gianneschi's team hypothesized, however, that a new kind of melanin -- enriched with selenium instead of sulfur -- would provide better protection against X-rays. Selenium is an essential micronutrient that plays an important role in cancer prevention, and previous research reports that selenium compounds can protect animals against radiation. These compounds are found in normal human proteins, but have not been associated with melanin in nature before. Gianneschi's team synthesized the new biomaterial, which they called "selenomelanin," and used it to treat living cells. For comparison, they also prepared cells treated with synthetic pheomelanin and eumelanin, as well as cells with no protective melanin. After receiving a dose of radiation that would be lethal to a human being, only the cells treated with selenomelanin still exhibited a normal cell cycle. "Our results demonstrated that selenomelanin offers superior protection from radiation," Gianneschi said. "We also found that it was easier to synthesize selenomelanin than pheomelanin, and what we created was closer than synthetic pheomelanin to the melanin found in nature." Further testing with bacteria showed that selenomelanin can be biosynthesized, meaning that live cells fed with appropriate nutrients can then produce selenomelanin on their own -- and retain its radioprotective properties. In fact, although the researchers synthesized selenomelanin in their lab, they believe it may already be present in nature. "With an abundant source of selenium in the environment, some organisms may have been able to adapt to extreme circumstances such radiation through the beneficial effects of selenomelanin," Gianneschi said. "Our work points to the possibility that melanin may act as a repository for selenium, helping ensure that organisms benefit from it," said Cao. "Selenomelanin may play an important role in how selenium is metabolized and distributed biologically. It's an area for further investigation." Gianneschi and his team envision that this new biomaterial could be applied to a person's skin, like a melanin-based sunscreen. It could also be used as a protective film to shield materials from radiation while in transit.

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  • Porous graphene ribbons doped with nitrogen for electronics and quantum computing

    A team of physicists and chemists has produced the first porous graphene ribbons in which specific carbon atoms in the crystal lattice are replaced with nitrogen atoms. These ribbons have semiconducting properties that make them attractive for applications in electronics and quantum computing, as reported by researchers from the Universities of Basel, Bern, Lancaster and Warwick in the Journal of the American Chemical Society. Graphene consists of a single layer of carbon atoms arranged in a honeycomb structure. The material is of interest not only in basic research but also for various applications given to its unique properties, which include excellent electrical conductivity as well as astonishing strength and rigidity. Research teams around the world are working to further expand these characteristics by substituting carbon atoms in the crystal lattice with atoms of different elements. Moreover, the electric and magnetic properties can also be modified by the formation of pores in the lattice. Ladder-like structure The individual building blocks are heated on a silver surface in order to synthesize a porous graphene ribbon that exhibits semiconducting properties and a ladder-like structure. In each rung of the ladder, two carbon atoms have been replaced with nitrogen atoms (blue). Source: University of Basel Now, a team of researchers led by the physicist Professor Ernst Meyer of the University of Basel and the chemist Dr. Shi-Xia Liu from the University of Bern have succeeded in producing the first graphene ribbons whose crystal lattice contains both periodic pores and a regular pattern of nitrogen atoms. The structure of this new material resembles a ladder, with each rung containing two atoms of nitrogen. In order to synthesize these porous, nitrogen-containing graphene ribbons, the researchers heated the individual building blocks step by step on a silver surface in a vacuum. The ribbons are formed at temperatures up to 220°C. Atomic force microscopy allowed the researchers not only to monitor the individual steps in the synthesis, but also to confirm the perfect ladder structure - and stability - of the molecule. Extraordinary properties Using scanning tunneling microscopy, the scientists from the Department of Physics and the Swiss Nanoscience Institute (SNI) at the University of Basel also demonstrated that these new graphene ribbons were no longer electrical conductors, like pure graphene, but actually behaved as semiconductors. Colleagues from the Universities of Bern and Warwick confirmed these findings by performing theoretical calculations of the electronic properties. "The semiconducting properties are essential for the potential applications in electronics, as their conductivity can be adjusted specifically," says Dr. Rémy Pawlak, first author of the study. From the literature, it is known that a high concentration of nitrogen atoms in the crystal lattice causes graphene ribbons to magnetize when subjected to a magnetic field. "We expect these porous, nitrogen-doped graphene ribbons to display extraordinary magnetic properties," says Ernst Meyer. "In the future, the ribbons could therefore be of interest for applications in quantum computing." Reference Pawlak et al., Bottom-up Synthesis of Nitrogen-Doped Porous Graphene Nanoribbons, Journal of the American Chemical Society (2020), http://dx.doi.org/10.1021/jacs.0c03946

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  • Graphene: It is all about the toppings

    The way graphene interacts with other materials depends on how these materials are brought into contact with the graphene. The appropriate atoms are brought into contact with the graphene in such a way that they 'grow' on the graphene in the desired crystal structure. Until now the mechanisms of the 'growth' of such other materials on graphene have often remained unclear. A new study shows now how indium oxide grows on graphene. Graphene consists of a single layer of carbon atoms. Exceptional electronic, thermal, mechanical and optical properties have made graphene one of the most studied materials at the moment. For many applications in electronics and energy technology, however, graphene must be combined with other materials: Since graphene is so thin, its properties drastically change when other materials are brought into direct contact with it. However, combining graphene with other materials at the molecular level is difficult: The way graphene interacts with other materials depends not only on which material you choose, but also on how these materials are brought into contact with the graphene. Rather than sticking a finished material layer to the graphene, the appropriate atoms are brought into contact with the graphene in such a way that they "grow" on the graphene in the desired crystal structure. Until now the mechanisms of the "growth" of such other materials on graphene have often remained unclear. A new joint study by research teams from the TU Wien and the University of Vienna for the first time observes now how indium oxide grows on graphene. The combination of indium oxide with graphene is important, for example for displays and sensors. The results have now been presented in the scientific journal "Advanced Functional Materials". Graphene pizza "As with a pizza, graphene technology is not only dependent on the graphene pizza base but also on its toppings," explains Bernhard C. Bayer from the Institute of Materials Chemistry at the TU Wien, who led the study. "How these toppings are applied to the graphene is, however, crucial." In most cases, atoms in the gaseous state are condensed on the graphene. In the case of indium oxide, these are indium and oxygen. "But there are many parameters such as background pressure, temperature or the speed at which these atoms are directed at the graphene that influence the result drastically," says Bernhard Bayer. "It is therefore important to develop a fundamental understanding of the chemical and physical processes that actually take place. But to do this, you have to watch the growth process as it proceeds. " This is exactly what the research team has now succeeded in doing: for the first time, the individual steps of growing indium oxide on graphene were observed in the electron microscope at atomic resolution. Randomly distributed or perfectly aligned "What was particularly interesting for us was the observation that, depending on the background pressure, the indium oxide crystallites either arrange themselves randomly on the graphene's crystal lattice or snap perfectly on one another like Lego bricks. This difference in arrangement can have a major impact on the application properties of the combined materials," says Kenan Elibol, first author of the study. The new findings will be useful to make the integration of graphene with other materials more predictable and controllable with respect to future application requirements. Reference Elibol et al., Process Pathway Controlled Evolution of Phase and Van-der-Waals Epitaxy in In/In2O3 on Graphene Heterostructures, Advanced Functional Materials, 2020, early view, https://doi.org/10.1002/adfm.202003300

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  • Scaling up the quantum chip

    MIT researchers have developed a process to manufacture and integrate "artificial atoms," created by atomic-scale defects in microscopically thin slices of diamond, with photonic circuitry, producing the largest quantum chip of its type. The accomplishment "marks a turning point" in the field of scalable quantum processors, says Dirk Englund, an associate professor in MIT's Department of Electrical Engineering and Computer Science. Millions of quantum processors will be needed to build quantum computers, and the new research demonstrates a viable way to scale up processor production, he and his colleagues note. Unlike classical computers, which process and store information using bits represented by either 0s and 1s, quantum computers operate using quantum bits, or qubits, which can represent 0, 1, or both at the same time. This strange property allows quantum computers to simultaneously perform multiple calculations, solving problems that would be intractable for classical computers. The qubits in the new chip are artificial atoms made from defects in diamond, which can be prodded with visible light and microwaves to emit photons that carry quantum information. The process, which Englund and his team describe in Nature, is a hybrid approach, in which carefully selected "quantum micro chiplets" containing multiple diamond-based qubits are placed on an aluminum nitride photonic integrated circuit. "In the past 20 years of quantum engineering, it has been the ultimate vision to manufacture such artificial qubit systems at volumes comparable to integrated electronics," Englund says. "Although there has been remarkable progress in this very active area of research, fabrication and materials complications have thus far yielded just two to three emitters per photonic system." Using their hybrid method, Englund and colleagues were able to build a 128-qubit system -- the largest integrated artificial atom-photonics chip yet. Other authors on the Nature paper include MIT researchers Noel H. Wan, Tsung-Ju Lu, Kevin C. Chen, Michael P. Walsh, Matthew E. Trusheim, Lorenzo De Santis, Eric A. Bersin, Isaac B. Harris, Sara L. Mouradian and Ian R. Christen; with Edward S. Bielejec at Sandia National Laboratories. Quality control for chiplets he artificial atoms in the chiplets consist of color centers in diamonds, defects in diamond's carbon lattice where adjacent carbon atoms are missing, with their spaces either filled by a different element or left vacant. In the MIT chiplets, the replacement elements are germanium and silicon. Each center functions as an atom-like emitter whose spin states can form a qubit. The artificial atoms emit colored particles of light, or photons, that carry the quantum information represented by the qubit. Diamond color centers make good solid-state qubits, but "the bottleneck with this platform is actually building a system and device architecture that can scale to thousands and millions of qubits," Wan explains. "Artificial atoms are in a solid crystal, and unwanted contamination can affect important quantum properties such as coherence times. Furthermore, variations within the crystal can cause the qubits to be different from one another, and that makes it difficult to scale these systems." Instead of trying to build a large quantum chip entirely in diamond, the researchers decided to take a modular and hybrid approach. "We use semiconductor fabrication techniques to make these small chiplets of diamond, from which we select only the highest quality qubit modules," says Wan. "Then we integrate those chiplets piece-by-piece into another chip that 'wires' the chiplets together into a larger device." The integration takes place on a photonic integrated circuit, which is analogous to an electronic integrated circuit but uses photons rather than electrons to carry information. Photonics provides the underlying architecture to route and switch photons between modules in the circuit with low loss. The circuit platform is aluminum nitride, rather than the traditional silicon of some integrated circuits. Using this hybrid approach of photonic circuits and diamond chiplets, the researchers were able to connect 128 qubits on one platform. The qubits are stable and long-lived, and their emissions can be tuned within the circuit to produce spectrally indistinguishable photons, according to Wan and colleagues. A modular approach While the platform offers a scalable process to produce artificial atom-photonics chips, the next step will be to "turn it on," so to speak, to test its processing skills. "This is a proof of concept that solid-state qubit emitters are very scalable quantum technologies," says Wan. "In order to process quantum information, the next step would be to control these large numbers of qubits and also induce interactions between them." The qubits in this type of chip design wouldn't necessarily have to be these particular diamond color centers. Other chip designers might choose other types of diamond color centers, atomic defects in other semiconductor crystals like silicon carbide, certain semiconductor quantum dots, or rare-earth ions in crystals. "Because the integration technique is hybrid and modular, we can choose the best material suitable for each component, rather than relying on natural properties of only one material, thus allowing us to combine the best properties of each disparate material into one system," says Lu. Finding a way to automate the process and demonstrate further integration with optoelectronic components such as modulators and detectors will be necessary to build even bigger chips necessary for modular quantum computers and multichannel quantum repeaters that transport qubits over long distances, the researchers say.

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  • Scientists develop unique polymer coating to tackle harmful fungi

    Scientists from the University of Nottingham have developed a new way to control harmful fungi, without the need to use chemical bioactives like fungicides or antifungals. Fungi cause diverse, serious societal and economic problems in the UK and globally. As well as causing fatal diseases in humans, fungi devastate food crops and spoil valuable products and materials. This has led to an antifungals/fungicide industry worth around $30bn globally. There are tight regulations around the use of fungicides and antifungals and there is also growing resistance of fungi to these agents. In a paper published today in Science Advances, experts from the University’s Schools of Life Sciences, Pharmacy, and Engineering, show how they have developed an innovative solution to tackle fungi, by passively blocking fungal attachment to surfaces using a coating of (meth)acrylate polymers, and so negating the need to use potentially harmful anti-fungals or other bioactive chemicals. Through previous work, the team found different combinations of fungicides which worked against fungi and also produced new understanding of preservative action against spoilage fungi. Although these advances meant less use of certain fungicides and chemicals, frequent tightening of regulations around usage are restricting the take up of technologies that still rely on bioactive agents, while spread of resistance worsens the problem. Consequently, potential bioactive-free technologies for combatting fungi are highly attractive to the industry. In this latest study, scientists show an alternative fungal control strategy, which doesn’t have the ‘killing affect’ of fungicides. The team identified polymers that resist the attachment of different kinds of fungi, including pathogens. They screened hundreds of (meth)acrylate polymers in high throughput, identifying several that reduce attachment of the human pathogen Candida albicans, the crop pathogen Botrytis cinerea, and other fungi. Although these advances meant less use of certain fungicides and chemicals, frequent tightening of regulations around usage are restricting the take up of technologies that still rely on bioactive agents, while spread of resistance worsens the problem. Consequently, potential bioactive-free technologies for combatting fungi are highly attractive to the industry. In this latest study, scientists show an alternative fungal control strategy, which doesn’t have the ‘killing affect’ of fungicides. The team identified polymers that resist the attachment of different kinds of fungi, including pathogens. They screened hundreds of (meth)acrylate polymers in high throughput, identifying several that reduce attachment of the human pathogen Candida albicans, the crop pathogen Botrytis cinerea, and other fungi. Professor Simon Avery, from the School of Life Sciences at the University is a lead investigator on the paper, he said: “This is the first high-throughput study of polymer chemistries resisting fungal attachment. “Our engagement to date with industry has highlighted a clear need for a new approach to control fungi and the major socioeconomic problems that they cause, as the value of existing strategies using bioactives (antifungals, fungicides) is eroded by growing resistance and regulations. “This passive, anti-attachment technology that we have been developing addresses this need."

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  • Machine learning reveals vulnerabilities in 3D-printed carbon-fiber composites

    NYU Tandon researchers use micro-CT imaging and machine learning to reconstruct toolpaths in 3D-printed composites, raising intellectual property concerns.

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  • The lightest shielding material in the world

    Empa researchers have succeeded in applying aerogels to microelectronics: Aerogels based on cellulose nanofibers can effectively shield electromagnetic radiation over a wide frequency range - and they are unrivalled in terms of weight. Electric motors and electronic devices generate electromagnetic fields that sometimes have to be shielded in order not to affect neighboring electronic components or the transmission of signals. High-frequency electromagnetic fields can only be shielded with conductive shells that are closed on all sides. Often thin metal sheets or metallized foils are used for this purpose. However, for many applications such a shield is too heavy or too poorly adaptable to the given geometry. The ideal solution would be a light, flexible and durable material with extremely high shielding effectiveness. Aerogels against electromagnetic radiation A sample of the electromagnetic shielding material made by Empa - a composite of cellulose nanofibres and silver nanowires. Image: Empa A breakthrough in this area has now been achieved by a research team led by Zhihui Zeng and Gustav Nyström. The researchers are using nanofibers of cellulose as the basis for an aerogel, which is a light, highly porous material. Cellulose fibres are obtained from wood and, due to their chemical structure, enable a wide range of chemical modifications. They are therefore a highly popular research object. The crucial factor in the processing and modification of these cellulose nanofibres is to be able to produce certain microstructures in a defined way and to interpret the effects achieved. These relationships between structure and properties are the very field of research of Nyström's team at Empa. The researchers have succeeded in producing a composite of cellulose nanofibers and silver nanowires, and thereby created ultra-light fine structures which provide excellent shielding against electromagnetic radiation. The effect of the material is impressive: with a density of only 1.7 milligrams per cubic centimeter, the silver-reinforced cellulose aerogel achieves more than 40 dB shielding in the frequency range of high-resolution radar radiation (8 to 12 GHz) - in other words: Virtually all radiation in this frequency range is intercepted by the material. Ice crystals control the shape Not only the correct composition of cellulose and silver wires is decisive for the shielding effect, but also the pore structure of the material. Within the pores, the electromagnetic fields are reflected back and forth and additionally trigger electromagnetic fields in the composite material, which counteract the incident field. To create pores of optimum size and shape, the researchers pour the material into pre-cooled moulds and allow it to freeze out slowly. The growth of the ice crystals creates the optimum pore structure for damping the fields. With this production method, the damping effect can even be specified in different spatial directions: If the material freezes out in the mould from bottom to top, the electromagnetic damping effect is weaker in the vertical direction. In the horizontal direction - i.e. perpendicular to the freezing direction - the damping effect is optimized. Shielding structures cast in this way are highly flexible: even after being bent back and forth a thousand times, the damping effect is practically the same as with the original material. The desired absorption can even be easily adjusted by adding more or less silver nanowires to the composite, as well as by the porosity of the cast aerogel and the thickness of the cast layer. The lightest electromagnetic shield in the world In another experiment, the researchers removed the silver nanowires from the composite material and connected their cellulose nanofibres with two-dimensional nanoplates of titanium carbide, which were produced using a special etching process. The nanoplates act like hard "bricks" that are joined together with flexible "mortar" made of cellulose fibers. This formulation was also frozen in cooled forms in a targeted manner. In relation to the weight of the material, no other material can achieve such shielding. This ranks the titanium carbide nanocellulose aerogel as by far the lightest electromagnetic shielding material in the world. Reference [1] Z Zeng, T Wu, D Han, Q Ren, G Siqueira, G Nyström; Ultralight, Flexible, and Biomimetic Nanocellulose/Silver Nanowire Aerogels for Electromagnetic Interference Shielding; ACS Nano (2020); doi: 10.1021/acsnano.9b07452 [2] Z Zeng, C Wang, G Siqueira, D Han, A Huch, S Abdolhosseinzadeh, J Heier, F Nüesch, CJ Zhang, G Nyström; Nanocellulose-MXene Biomimetic Aerogels with Orientation-Tunable Electromagnetic Interference Shielding Performance; Advanced Science (2020); doi: 10.1002/advs.202000979

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  • Flexible material shows potential for use in fabrics to heat, cool

    A new North Carolina State University study finds that a material made of carbon nanotubes has a combination of thermal, electrical and physical properties that make it an appealing candidate for next-generation smart fabrics. A film made of tiny carbon nanotubes (CNT) may be a key material in developing clothing that can heat or cool the wearer on demand. A new North Carolina State University study finds that the CNT film has a combination of thermal, electrical and physical properties that make it an appealing candidate for next-generation smart fabrics. The researchers were also able to optimize the thermal and electrical properties of the material, allowing the material to retain its desirable properties even when exposed to air for many weeks. Moreover, these properties were achieved using processes that were relatively simple and did not need excessively high temperatures. "Many researchers are trying to develop a material that is non-toxic and inexpensive, but at the same time is efficient at heating and cooling," said Tushar Ghosh, co-corresponding author of the study. "Carbon nanotubes, if used appropriately, are safe, and we are using a form that happens to be inexpensive, relatively speaking. So it's potentially a more affordable thermoelectric material that could be used next to the skin." Ghosh is the William A. Klopman Distinguished Professor of Textiles in NC State's Wilson College of Textiles. "We want to integrate this material into the fabric itself," said Kony Chatterjee, first author of the study and a Ph.D. student at NC State. "Right now, the research into clothing that can regulate temperature focuses heavily on integrating rigid materials into fabrics, and commercial wearable thermoelectric devices on the market aren't flexible either." To cool the wearer, Chatterjee said, CNTs have properties that would allow heat to be drawn away from the body when an external source of current is applied. "Think of it like a film, with cooling properties on one side of it and heating on the other," Ghosh said. The researchers measured the material's ability to conduct electricity, as well as its thermal conductivity, or how easily heat passes through the material. One of the biggest findings was that the material has relatively low thermal conductivity - meaning heat would not travel back to the wearer easily after leaving the body in order to cool it. That also means that if the material were used to warm the wearer, the heat would travel with a current toward the body, and not pass back out to the atmosphere. The researchers were able to accurately measure the material's thermal conductivity through a collaboration with the lab of Jun Liu, an assistant professor of mechanical and aerospace engineering at NC State. The researchers used a special experimental design to more accurately measure the material's thermal conductivity in the direction that the electric current is moving within the material. "You have to measure each property in the same direction to give you a reasonable estimate of the material's capabilities," said Liu, co-corresponding author of the study. "This was not an easy task; it was very challenging, but we developed a method to measure this, especially for thin flexible films." The research team also measured the ability of the material to generate electricity using a difference in temperature, or thermal gradient, between two environments. Researchers said that they could take advantage of this for heating, cooling, or to power small electronics. Liu said that while these thermoelectric properties were important, it was also key that they found a material that was also flexible, stable in air, and relatively simple to make. "The point of this paper isn't that we achieved the best thermoelectric performance," Liu said. "We achieved something that can be used as a flexible, electronic, soft material that's easy to fabricate. It's easy to prepare this material, and easy to achieve these properties." Ultimately, their vision for the project is to design a smart fabric that can heat and cool the wearer, along with energy harvesting. They believe that a smart garment could help reduce energy consumption. "Instead of heating or cooling a whole dwelling or space, you would heat or cool the personal space around the body," Ghosh said. "If we could get the thermostat down a degree or two, that could save a tremendous amount of energy." Reference Chatterjee et al., In-plane Thermoelectric Properties of Flexible and Room Temperature Processable Doped Carbon Nanotube Films, ACS Applied Energy Materials (2020), https://doi.org/10.1021/acsaem.0c00995

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  • Carbon-loving materials designed to reduce industrial emissions

    Researchers at Oak Ridge National Laboratory and the University of Tennessee, Knoxville, demonstrated a novel fabrication method for affordable gas membranes that can remove carbon dioxide from industrial emissions. Image: Zhenzhen Yang/University of Tennessee Researchers at the Department of Energy's Oak Ridge National Laboratory and the University of Tennessee, Knoxville, are advancing gas membrane materials to expand practical technology options for reducing industrial carbon emissions. Results published in Chem demonstrate a fabrication method for membrane materials that can overcome current bottlenecks in selectivity and permeability, key variables that drive carbon-capturing performance in real environments. "Often there is a trade-off in how selective or how permeable you can make membranes that filter out carbon dioxide without allowing other gases to pass through. The ideal scenario is to create materials with high permeability and selectivity," said Zhenzhen Yang of UT's Department of Chemistry. Gas membranes are a promising but still developing technology for reducing post-combustion or flue gas emissions produced by fossil-fueled industries. The concept is simple: a thin, porous membrane acts as a filter for exhaust gas mixtures, selectively allowing carbon dioxide, or CO2, to flow through freely into a collector that is kept under reduced pressure, but preventing oxygen, nitrogen and other gases from tagging along. Unlike existing chemical methods to capture CO2 from industrial processes, membranes are easy to install and can operate unattended for long periods with no additional steps or added energy costs. The catch is that new, cost-effective materials are needed to scale up the technology for commercial adoption. "Gas membranes need pressure on one side and typically a vacuum on the other to maintain a free-flow environment, which is why materials' selectivity and permeability are so important to developing the technology," said Ilja Popovs of ORNL's Chemical Sciences Division. "Underperforming materials require more energy to push gases through the system, so advanced materials are key to keeping energy costs low." No natural and only a few synthetic materials have exceeded what is called the Robeson upper limit, a known boundary that constrains how selective and permeable most materials can be before these rates start to drop. Materials with sufficiently high selectivity and permeability for efficient gas separations are rare and often made from expensive starting materials whose production requires either long and tedious synthesis or costly transition metal catalysts. "We set out to test a hypothesis that introducing fluorine atoms into membrane materials could improve carbon-capture and separation performance," Yang said. The element fluorine, used to make consumer products such as Teflon and toothpaste, offers carbon dioxide-philic properties that make it attractive for carbon-capture applications. It is also widely available, making it a relatively affordable option for low-cost fabrication methods. Research on fluorinated gas membranes has been limited because of fundamental challenges of incorporating fluorine into materials to realize its carbon-loving functionality. "Our first step was to create a unique fluorine-based polymer using simple chemical methods and commercially available starting materials," Yang said. Next, researchers transformed, or carbonized, the material using heat to give it the porous structure and functionality needed for capturing CO2. The two-step process preserved the fluorinated groups and boosted CO2 selectivity in the final material, overcoming a fundamental hurdle encountered in other synthetic methods. "The approach resulted in a carbon dioxide-philic material with high surface area and ultra-micropores that is stable in high-temperature operating conditions," Yang said. "All of these factors make it a promising candidate for carbon-capture and separation membranes." The material's novel design contributes to its exceptional performance, observed in high selectivity and permeability rates that exceed the Robeson upper limit, something only a handful of materials have accomplished. "Our success was a material achievement that demonstrates feasible routes for leveraging fluorine in future membrane materials. Moreover, we achieved this goal using commercially available, inexpensive starting materials," Popovs said. The basic discovery expands the limited library of practical options for carbon-capture membranes and opens new directions for developing fluorinated membranes with other task-specific functionalities. Researchers aim to next investigate the mechanism by which fluorinated membranes absorb and transport CO2, a fundamental step that will inform the design of better carbon-capture systems with materials purposely tailored to grab CO2 emissions. Reference Yang et al., Surpassing Robeson Upper Limit for CO2/N2 Separation with Fluorinated Carbon Molecular Sieve Membranes, Chem (2020), http://dx.doi.org/10.1016/j.chempr.2019.12.006

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  • Electrons in the fast lane

    Along microscopic structures in perovskite solar cells electrons can move faster. Image: MPI-P Solar cells based on perovskite compounds could soon make electricity generation from sunlight even more efficient and cheaper. The laboratory efficiency of these perovskite solar cells already exceeds that of the well-known silicon solar cells. An international team led by Stefan Weber from the Max Planck Institute for Polymer Research (MPI-P) in Mainz has found microscopic structures in perovskite crystals that can guide the charge transport in the solar cell. Clever alignment of these "electron highways" could make perovskite solar cells even more powerful. Solar cells convert sunlight into electricity. During this process, the electrons of the material inside the cell absorb the energy of the light. Traditionally, this light-absorbing material is silicon, but perovskites could prove to be a cheaper alternative. The electrons excited by the sunlight are collected by special contacts on the top and bottom of the cell. However, if the electrons remain in the material for too long, they can lose their energy again. To minimize losses, they should therefore reach the contacts as quickly as possible. Microscopically small structures in the perovskites - so-called "ferroelastic twin domains" - can influence how fast the electrons move. An international research group led by Stefan Weber at the Max Planck Institute for Polymer Research in Mainz discovered this phenomenon. The stripe-shaped structures that the scientists investigated form spontaneously during the fabrication of the perovskite by mechanical stress in the material. By combining two microscopy methods, the researchers were able to show that electrons move much faster parallel to the stripes than perpendicular to them. "The domains act as tiny highways for electrons," compares Stefan Weber. For their experiments, the researchers first had to visualize the stripe-shaped domains. They succeeded in doing this with a piezo force microscope (PFM). Five years ago, Weber and his colleagues discovered the domains for the first time in a perovskite crystal using this method. "Back then, we already wondered whether the structures had an influence on the operation of a perovskite solar cell," Weber explains. "Our latest results now show that this is the case." The breakthrough came when the researchers compared their PFM images with data obtained from another method called photoluminescence microscopy. "Our photoluminescence detector works like a speed trap," explains Ilka Hermes, researcher in Weber's group and first author of the study. "We use it to measure the speed of electrons in different directions at the microscopic level." Hermes discovered that along the stripes the electrons moved about 50 to 60% faster than perpendicular to them. "If we were able to make the stripes point directly to the electrodes, a perovskite solar cell could become much more efficient," concludes Hermes. The researchers have now published their results in the journal "Energy Environmental Science". With the new results, not only solar cells could be improved. Other optoelectronic applications such as light-emitting diodes or radiation detectors could also benefit from directed charge transport. "In general, it is an advantage if we can direct the electrons in the right direction," explains Stefan Weber. The researchers' idea: to put perovskite crystals under mechanical stress during their production. This so-called "strain engineering" would enable an optimized orientation of the electron highways. Referenz Ilka M. Hermes, Andreas Best, Leonard Winkelmann, Julian Mars, Sarah M. Vorpahl, Markus Mezger, Liam Collins, Hans-Jürgen Butt, David S. Ginger, Kaloian Koynov, Stefan A. L. Weber: Anisotropic carrier diffusion in single MAPbI3 grains correlates to their twin domains (Energy & Environmental Science); https://dx.doi.org/10.1039/D0EE01016B

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