) Imprimarea 3D prin scrierea directă cu laser permite producerea de structuri cu dimensiuni micro-metrice pentru multe aplicații, de la biomedicină la microelectronică până la metamateriale optice. Cercetătorii de la Institutul de Tehnologie din Karlsruhe (KIT) au dezvoltat acum cerneluri 3D care pot fi șterse selectiv. Acest lucru permite degradarea și reasamblarea specifică a structurilor foarte precise pe micrometrele și pe scalele nanometrice.
Posted: Aug 14, 2018
3D inks that can be erased selectively
(Nanowerk News) 3D printing by direct laser writing enables production of micro-meter-sized structures for many applications, from biomedicine to microelectronics to optical metamaterials. Researchers of Karlsruhe Institute of Technology (KIT) have now developed 3D inks that can be erased selectively. This allows specific degradation and reassembly of highly precise structures on the micrometer and nanometer scales.
3D printing is gaining importance, as it allows for the efficient manufacture of complex geometries. A very promising method is direct laser writing: a computer-controlled focused laser beam acts as a pen and produces the desired structure in a photoresist. In this way, three-dimensional structures with details in the sub-micrometer range can be produced.
“The high resolution is very attractive for applications requiring very precise filigree structures, such as in biomedicine, microfluidics, microelectronics or for optical metamaterials,” say Professor Christopher Barner-Kowollik, Head of the Macromolecular Architectures Group of KIT’s Institute for Chemical Technology and Polymer Chemistry (ITCP) and of the Soft Matter Materials Group of Queensland University of Technology (QUT) in Brisbane, Australia, and Dr. Eva Blasco of the ITCP of KIT.
Over a year ago, KIT researchers already succeeded in expanding the possibilities of direct laser writing: the working groups of Professor Martin Wegener at the Institute of Applied Physics (APH) and the Institute of Nanotechnology (INT) of KIT and of Professor Christopher Barner-Kowollik developed an erasable ink for 3D printing. Thanks to reversible binding, the building blocks of the ink can be separated again.
Now, the scientists from Karlsruhe and Brisbane have largely refined their development. As reported in the journal Nature Communications, they have developed several inks, in different colors so to speak, that can be erased independently of each other. This enables selective and sequential degradation and reassembly of the laser-written microstructures.
In case of highly complex constructions, for instance, temporary supports can be produced and removed again later on. It may also be possible to add or remove parts to or from three-dimensional scaffolds for cell growth, the objective being to observe how the cells react to such changes. Moreover, the specifically erasable 3D inks allow for the exchange of damaged or worn parts in complex structures.
When producing the cleavable photoresists, the researchers were inspired by degradable biomaterials. The photoresists are based on silane compounds that can be cleaved easily. Silanes are silicon-hydrogen compounds. The scientists used specific atom substitution for preparing the photoresists. In this way, microstructures can be degraded specifically under mild conditions without structures with other material properties being damaged.
This is the major advantage over formerly used erasable 3D inks. New photoresists also contain the monomer pentaerythritol triacrylate that significantly enhances writing without affecting cleavability.
Aceste progrese, făcute de mediul colaborativ al platformei Grafene, ar putea conduce la aplicații promițătoare în senzori, în optoelectronică și în dispozitive flexibile. Cercetătorii visează acum dispozitive hibride multifuncționale de înaltă performanță sub controlul celei mai abundente și puternice surse de lumină energetică a naturii.Această moleculă – un spiropyran capabil să poată fi redată prin imagine – poate fi apoi ancorată la suprafața materialelor cum ar fi grafenul sau disulfura de molibden, generând astfel o superlattică macroscopică hibridă precis atomică. Când este iluminat, întreaga structură supramoleculară are o rearanjare structurală colectivă, care poate fi vizualizată direct cu o rezoluție sub-nanometrică prin scanarea microscopiei de tunel.
Posted: Aug 14, 2018
Flipping the switch on supramolecular electronics
(Nanowerk News) Graphene and related materials hold great potential for technological applications such as electronics, sensors, and energy storage devices, among others. Thanks to their high surface sensitivity, these materials are an ideal platform to study the interplay between molecular assemblies at the nanoscale and macroscopic electrical phenomena.
This molecule – a photoswitchable spiropyran – can be then anchored to the surface of materials such as graphene or molybdenum disulfide, thus generating an atomically precise hybrid macroscopic superlattice. When illuminated, the whole supramolecular structure experiences a collective structural rearrangement, which could be directly visualized with a sub-nanometer resolution by scanning tunneling microscopy.
More importantly, this light-induced reorganization at the molecular level induces large changes in the macroscopic electrical properties of the hybrid devices. The molecules, together with the layers of graphene and related materials, can convert single-molecule events into a spatially homogeneous switching action that generates a macroscopic electrical response. This novel and versatile approach takes supramolecular electronics to the next level.
Photo-switchable molecular crystals in two dimensions. (click on image to enlarge)
‘Thanks to this new approach, we can exploit the capacity of collective switching events occurring in superlattices of photochromic molecules assembled onto graphene and related materials to induce large scale and reversible modulation in the electrical properties of high-performance opto-electronic devices,’ explains Paolo Samorì, lead author of the paper. ‘This technology could find applications in the next generation of smart and portable electronics, with programmable properties,’ he adds.
Samorì also explains how this idea of tailoring molecular superlattices could generate a wide variety of new materials with tunable and responsive properties. ‘To dial your functions! You only need to carefully choose the right molecules, the thus-formed superlattice will allow to maximize the change in properties as a response to external inputs,’ he says.
Vittorio Pellegrini, researcher at IIT and Division Leader for Energy, Composites, and Production at the Graphene Flagship, highlights how the research is ‘unique in the way it combines graphene and other related materials with light-responsive chemical molecules. These macroscopic arrangements are promising platforms for optoelectronics.’ Pellegrini points out the outstanding potential of these new findings: ‘the molecular ultra-thin coating can be tailored just by synthesizing different molecules.’ Moreover, ‘this discovery will lead us to the development of devices, as the technique developed by Samorì and his team can be scaled up in reproducible manner,’ he added. Samorì agrees: ‘The limit in the scalability is the accessibility to ultra-flat and atomically precise graphene and related materials.’
These advances, made possible by the collaborative environment of the Graphene Flagship, could lead to promising applications in sensors, optoelectronics, and flexible devices. Researchers now dream of high-performance multifunctional hybrid devices under control of nature’s most abundant and powerful source of energy – light.
Professor Andrea C. Ferrari, Science and Technology Officer of the Graphene Flagship, and Chair of its management panel added: ‘Supra-molecular chemistry has been part of the Flagship research since the very beginning. Over the years our partners have improved and developed the techniques that enable to interface molecules with graphene and related materials. We are now witnessing a steady progress towards applications, as shown by this interesting work.’
Un gel nou, super-izolator dezvoltat de cercetatorii de la Universitatea din Colorado Boulder ar putea creste dramatic eficienta energetica a zgarie-nori si a altor cladiri si ar putea ajuta intr-o zi oamenii de stiinta sa construiasca habitate de sera pentru coloniști pe Marte. „Aerogelul”, care seamănă cu o lentilă de contact plată din plastic, este atât de rezistent la căldură încât să-i poți pune o bandă pe mâna ta și să aprinzi focul fără să simți nimic
Posted: Aug 13, 2018
From office windows to Mars: Scientists debut super-insulating gel
(Nanowerk News) A new, super-insulating gel developed by researchers at the University of Colorado Boulder could dramatically increase the energy efficiency of skyscrapers and other buildings, and might one day help scientists to build greenhouse-like habitats for colonists on Mars. The “aerogel,” which looks like a flattened plastic contact lens, is so resistant to heat that you could put a strip of it on your hand and light a fire on top without feeling a thing. But unlike similar products on the market, the material is mostly see-through (Nano Energy, „Flexible transparent aerogels as window retrofitting films and optical elements with tunable birefringence”).
“Transparency is an enabling feature because you can use this gel in windows, and you could use it in extraterrestrial habitats,” said Ivan Smalyukh, a professor in the Department of Physics. “You could harvest sunlight through that thermally insulating material and store the energy inside, protecting yourself from those big oscillations in temperature that you have on Mars or on the moon.”
The group’s gel is also cheaper to produce because it comes from humble beginnings: beer waste.
Aerogels are at least 90 percent gas by weight, Smalyukh explained, but their defining feature is air. Their thin films are made up of crisscrossing patterns of solid material that trap air inside billions of tiny pores, similar to the bubbles in bubble wrap. It’s that trapping capacity that makes them such good insulators.
“You create a very tortuous network of these nanoparticles that link together in the aerogel, preventing the heat from going through,” Smalyukh said.
Most currently available aerogels, however, are opaque—a big problem if you want to use them to coat windows.
To make a different type of gel, Smalyukh and his colleagues begin with the common plant sugar cellulose. By carefully controlling how cellulose molecules link up, the team is able to orient them into a lattice-like pattern. That pattern is so uniform, he said, that it allows light to pass through unbothered, giving the gel its transparent appearance.
Researchers can make cellulose by adding specialized bacteria to a wide range of food waste. The team has been driving to breweries across the Boulder area to collect tubs of beer wort, or the waste liquid produced during the brewing process.
“So not only are we recycling and saving this valuable material from entering the landfill, but we’re also producing this raw material cheaply,” said Andrew Hess, a Ph.D. student in physics at CU Boulder.
The final product of the team’s efforts is a thin, flexible film that is roughly 100 times lighter than glass.
That could be especially useful for buildings in the United States. According to the Department of Energy, roughly one-quarter of the energy that is expended to heat and cool buildings in the country goes toward offsetting the loss of heat through windows, potentially costing building operators billions of dollars per year.
“We’re envisioning a retrofitting product that would basically be a peel-and-stick film that a consumer would buy at Home Depot,” Hess said.
Smalyukh and his colleagues have been exploring partnerships with window manufacturing companies and earlier this summer, their project was named one of the winners of NASA’s 2018 iTech competition. This national contest seeks out Earth-bound technologies that might one day help people travel to space.
“Our approach so far has been around windows,” Hess said. “However, we also see our technology being enabling for so many other applications, including smart clothes, for insulating cars and protecting firefighters.”
Source: By Daniel Strain, University of Colorado Boulder
chimiștii au demonstrat că trei structuri de carbon create recent de către oamenii de știință din Coreea de Sud și Japonia sunt, de fapt, schwarzi-urile căutate de mult timp, pe care cercetătorii le prezică că vor avea proprietăți electrice unice și de stocare cum ar fi cele descoperite acum în buckminsterfullerenes sau fullerene pentru scurt), nanotuburi și grafen.
Noile structuri au fost construite în interiorul porilor de zeoliți, forme cristaline de dioxid de siliciu – nisip – utilizat mai frecvent ca dedurizatori de apă în detergenții de rufe și pentru a crăpa catalitic petrolul în benzină. Denumit carbonul zeolit-template (ZTC), structurile au fost investigate pentru posibile proprietăți interesante, deși creatorii nu au fost conștienți de identitatea lor ca schwarzites, pe care chimistii teoretici au lucrat timp de decenii.
Posted: Aug 13, 2018
Long-sought carbon structure ‘schwarzite’ joins graphene, fullerene family
(Nanowerk News) The discovery of buckyballs surprised and delighted chemists in the 1980s, nanotubes jazzed physicists in the 1990s, and graphene charged up materials scientists in the 2000s, but one nanoscale carbon structure – a negatively curved surface called a schwarzite – has eluded everyone. Until now.
University of California, Berkeley, chemists have proved that three carbon structures recently created by scientists in South Korea and Japan are in fact the long-sought schwarzites, which researchers predict will have unique electrical and storage properties like those now being discovered in buckminsterfullerenes (buckyballs or fullerenes for short), nanotubes and graphene.
The new structures were built inside the pores of zeolites, crystalline forms of silicon dioxide – sand – more commonly used as water softeners in laundry detergents and to catalytically crack petroleum into gasoline. Called zeolite-templated carbons (ZTC), the structures were being investigated for possible interesting properties, though the creators were unaware of their identity as schwarzites, which theoretical chemists have worked on for decades.
Carbon atoms (black) assembling on the molecular surface of a zeolite (red oxygen atoms and yellow silicon atoms) to form a negatively curved schwarzite. (Graphics by Yongjin Lee and Efrem Braun)
Based on this theoretical work, chemists predict that schwarzites will have unique electronic, magnetic and optical properties that would make them useful as supercapacitors, battery electrodes and catalysts, and with large internal spaces ideal for gas storage and separation.
UC Berkeley postdoctoral fellow Efrem Braun and his colleagues identified these ZTC materials as schwarzites based of their negative curvature, and developed a way to predict which zeolites can be used to make schwarzites and which can’t.
“We now have the recipe for how to make these structures, which is important because, if we can make them, we can explore their behavior, which we are working hard to do now,” said Berend Smit, an adjunct professor of chemical and biomolecular engineering at UC Berkeley and an expert on porous materials such as zeolites and metal-organic frameworks.
Smit, the paper’s corresponding author, Braun and their colleagues in Switzerland, China, Germany, Italy and Russia will report their discovery this week in the journal Proceedings of the National Academy of Sciences („Generating carbon schwarzites via zeolite-templating „). Smit is also a faculty scientist at Lawrence Berkeley National Laboratory.
Playing with carbon
Diamond and graphite are well-known three-dimensional crystalline arrangements of pure carbon, but carbon atoms can also form two-dimensional “crystals” — hexagonal arrangements patterned like chicken wire. Graphene is one such arrangement: a flat sheet of carbon atoms that is not only the strongest material on Earth, but also has a high electrical conductivity that makes it a promising component of electronic devices.
The cage structure of a schwarzite that was formed inside the pores of a zeolite. The zeolite is subsequently dissolved to release the new material. (Image: Yongjin Lee and Efrem Braun)
Graphene sheets can be wadded up to form soccer ball-shaped fullerenes – spherical carbon cages that can store molecules and are being used today to deliver drugs and genes into the body. Rolling graphene into a cylinder yields fullerenes called nanotubes, which are being explored today as highly conductive wires in electronics and storage vessels for gases like hydrogen and carbon dioxide. All of these are submicroscopic, 10,000 times smaller than the width of a human hair.
To date, however, only positively curved fullerenes and graphene, which has zero curvature, have been synthesized, feats rewarded by Nobel Prizes in 1996 and 2010, respectively.
In the 1880s, German physicist Hermann Schwarz investigated negatively curved structures that resemble soap-bubble surfaces, and when theoretical work on carbon cage molecules ramped up in the 1990s, Schwarz’s name became attached to the hypothetical negatively curved carbon sheets.
“The experimental validation of schwarzites thus completes the triumvirate of possible curvatures to graphene; positively curved, flat, and now negatively curved,” Braun added.
Minimize me
Like soap bubbles on wire frames, schwarzites are topologically minimal surfaces. When made inside a zeolite, a vapor of carbon-containing molecules is injected, allowing the carbon to assemble into a two-dimensional graphene-like sheet lining the walls of the pores in the zeolite. The surface is stretched tautly to minimize its area, which makes all the surfaces curve negatively, like a saddle. The zeolite is then dissolved, leaving behind the schwarzite.
A computer-rendered negatively curved soap bubble that exhibits the geometry of a carbon schwarzite. (Image: Felix Knöppel)
“These negatively-curved carbons have been very hard to synthesize on their own, but it turns out that you can grow the carbon film catalytically at the surface of a zeolite,” Braun said. “But the schwarzites synthesized to date have been made by choosing zeolite templates through trial and error. We provide very simple instructions you can follow to rationally make schwarzites and we show that, by choosing the right zeolite, you can tune schwarzites to optimize the properties you want.”
Researchers should be able to pack unusually large amounts of electrical charge into schwarzites, which would make them better capacitors than conventional ones used today in electronics. Their large interior volume would also allow storage of atoms and molecules, which is also being explored with fullerenes and nanotubes. And their large surface area, equivalent to the surface areas of the zeolites they’re grown in, could make them as versatile as zeolites for catalyzing reactions in the petroleum and natural gas industries.
Braun modeled ZTC structures computationally using the known structures of zeolites, and worked with topological mathematician Senja Barthel of the École Polytechnique Fédérale de Lausanne in Sion, Switzerland, to determine which of the minimal surfaces the structures resembled.
The team determined that, of the approximately 200 zeolites created to date, only 15 can be used as a template to make schwarzites, and only three of them have been used to date to produce schwarzite ZTCs. Over a million zeolite structures have been predicted, however, so there could be many more possible schwarzite carbon structures made using the zeolite-templating method.
Universitatea din Texas de la Arlington a brevetat o piele inteligenta, creata de un cercetator UTA, care va da robotilor senzatii tactile mai sensibile decat oameni.Pielea inteligenta este de fapt alcatuita din milioane de senzori de nanofire flexibile care au mult mai multe informatii decat pielea oamenilor. Pe măsură ce senzorii perie o suprafață, robotul colectează toate informațiile pe care senzorii le trimit înapoi.Alte aplicații posibile viitoare includ aderarea pielii inteligente la proteze pentru a le dota cu un sentiment, aplicarea tehnologiei pe alte dispozitive medicale, țeserea pielii în uniforma unui soldat de luptă, astfel încât să poată fi detectată orice substanță chimică toxică sau identificarea amprentelor digitale.
Posted: Aug 09, 2018
Flexible nanowire sensors give robots ultra-sensitive skin
(Nanowerk News) The University of Texas at Arlington has patented a smart skin, created by a UTA researcher, that will give robots more sensitive tactile feeling than humans.
“The idea is to have robots work better alongside people,” said Zeynep Çelik-Butler, a UTA electrical engineering professor. “The smart skin is actually made up of millions of flexible nanowire sensors that take in so much more information than people’s skin. As the sensors brush against a surface, the robot collects all the information those sensors send back.”
Çelik-Butler said the sensors, which are flexible and made of zinc oxide nanorods, are self-powered and do not need any external voltage for operation. Each is about 0.2 microns in diameter, while a human hair is about 40 to 50 microns.
In addition, the developed sensors were fully packaged in a chemical and moisture resistant polyimide that greatly enhances usability in harsh environments. The result is a thin, flexible, self-powered tactile sensing layer, suitable as a robotic or prosthetic skin.
Smart skin technology. (Image: UTA)
The smart skin technology allows the robots to sense temperature changes and surface variations, which would allow a person alongside the robot to be safer or react accordingly.
Other possible future applications include adhering the smart skin to prosthetics to equip them with some feeling, applying the technology to other medical devices, weaving the skin into the uniform of a combat soldier so that any toxic chemicals could be detected or fingerprint identification.
“These sensors are highly sensitive and if they were brushed over a partial fingerprint, the technology could help identify who that person is,” Çelik-Butler said. “Imagine people being able to ascertain a person’s identity with this hairy robot, as my students call it.”
Teri Schultz, director of technology management in the UTA Office of Research, said the technology shows promise in a number of commercial sectors.
“Robots are the here and now,” Schultz said. “We could see this technology develop with the next generation of robots to allow them to be more productive in helping people.”
Un material care constă în atomi dintr-un singur element, dar are proprietăți complet diferite în funcție de aranjamentul atomic – acest lucru poate părea ciudat, dar este de fapt realitate cu nano-panglici graphene. Panglicile, care au doar câțiva atomi de carbon și un singur atom gros, au proprietăți electronice foarte diferite, în funcție de forma și lățimea lor: conductor, semiconductor sau izolator.
Posted: Aug 09, 2018
Quantum chains in graphene nanoribbons
(Nanowerk News) Empa researchers, together with researchers from the Max Planck Institute for Polymer Research in Mainz and other partners, have achieved a breakthrough that could in future be used for precise nanotransistors or – in the distant future – possibly even quantum computers, as the team reports in the current issue of the scientific journal Nature („Engineering of robust topological quantum phases in graphene nanoribbons”).
When graphene nanoribbons contain sections of varying width, very robust new quantum states can be created in the transition zone.
A material that consists of atoms of a single element, but has completely different properties depending on the atomic arrangement – this may sound strange, but is actually reality with graphene nano-ribbons. The ribbons, which are only a few carbon atoms wide and exactly one atom thick, have very different electronic properties depending on their shape and width: conductor, semiconductor or insulator.
An international research team led by Empa’s „nanotech@surfaces” laboratory has now suc-ceeded in precisely adjusting the properties of the ribbons by specifically varying their shape. The particular feature of this technology is that not only can the „usual” electronic properties mentioned above be varied – it can also be used to generate specific local quantum states.
So what’s behind it? If the width of a narrow graphene nanoribbon changes, in this case from seven to nine atoms, a special zone is created at the transition: because the electronic properties of the two areas differ in a special, so-called topological way, a „protected” and thus very robust new quantum state is created in the transition zone. This local electronic quantum state can now be used as a basic component to produce tailor-made semiconductors, metals or insulators – and possibly even as a component in quantum computers.
The Empa researchers under the lead of Oliver Gröning were able to show that if these ribbons are built with regularly alternating zones of different widths, a chain of interlinked quantum states with its own electronic structure is created by the numerous transitions. The exciting thing is that the electronic properties of the chain change depending on the width of the different segments. This allows them to be finely adjusted – from conductors to semiconductors with different bandgaps. This principle can be applied to many different types of transition zones – for example, from seven to eleven atoms.
„The importance of this development is also underlined by the fact that a research group at the University of California, Berkeley, came to similar results independently of us,” said Gröning. The work of the US research team has been published in the same issue of Nature .
On the way to nanoelectronics
Based on these novel quantum chains, precise nano-transistors could be manufactured in the future – a fundamental step on the way to nanoelectronics. Whether the switching distance between the „1” state and the „0” state of the nanotransistor is actually large enough depends on the bandgap of the semiconductor – and with the new method this can be set almost at will.
The electronic properties of the chain can be finely adjusted.
In reality, however, this is not quite as simple: for the chain to have the desired electronic properties, each of the several hundred or even thousands of atoms must be in the right place.
„This is based on complex, interdisciplinary research, ” says Empa researcher Gröning. „Researchers from different disciplines in Dübendorf, Mainz, Dresden, and Troy (USA) worked together – from theoretical understanding and specific knowledge of how precursor molecules have to be built and how structures on surfaces can be selectively grown to structural and electronic analysis using a scanning tunneling microscope.”
An excursion into the quantum realm
Ultrasmall transistors – and thus the next step in the further miniaturization of electronic circuits – are the obvious application possibilities here: although they are technically challenging, electronics based on nanotransistors actually work fundamentally the same as today’s microelectronics.
The semiconducting nanoribbons produced by the Empa researchers would allow transistors with a channel cross-section 1,000 times smaller than typically manufactured today. However, further possibilities can also be imagined, for example in the field of spintronics or even quantum informatics.
Top: Schematic representation of the production of hybrid nanobands using two different precursor molecules. The left (small) produces a smooth 7-carbon atom wide nanoband. The larger one produces a 7-11 atom wide, caroform segment. Atomic force microscopy: Atomic force microscope image of a hybrid graphene nanoband with 5 „diamond” segments (7-11 segments) in the middle which is continued left and right by smooth 7-nanobands. The black scale bar is 1 nm long. Scanning tunnel spectroscopy: Spectroscopic image of the localized quantum states (bright regions) at both ends of the diamond region. The section corresponds to that of the atomic force microscope image. Simulation of the scanning tunnel spectroscopy: Theoretical prediction of how the quantum states to be expected at the end of the diamond segment should look in the experiment.
This is because the electronic quantum states at junctions of graphene nanoribbons of different widths can also carry a magnetic moment. This could make it possible to process information not by charge as was previously customary, but by the so-called spin – in the figurative sense the „direction of rota-tion” of the state. And the development could even go one step further.
„We have observed that topological end states occur at the ends of certain quantum chains. This offers the possibility of using them as elements of so-called qubits – the complex, interlocked states in a quantum computer,” explains Oliver Gröning.
Today and tomorrow, however, no quantum computer is built from nanoribbons – there is still a lot of research needed, says Gröning: „The possibility of flexibly adjusting the electronic properties through the targeted combination of individual quantum states represents a major leap for us in the production of new materials for ultra-miniaturized transistors.”
The fact that these materials are stable under environmental conditions plays an important role in the development of future applications.
„The further-reaching potential of the chains to create local quantum states and link them together in a targeted manner is also fascinating,” Gröning continues. „Whether this potential can actually be exploited for future quantum computers remains to be seen, however. It is not enough to create localized topological states in the nanoribbons – these would also have to be coupled with other materials such as superconductors in such a way that the conditions for qubits are actually met.”
creat materiale care pot stoca energie în acest fel, pot fi stoarse în mod repetat, fără a se deteriora și chiar schimba forma, dacă este necesar.
Aceste tipuri de materiale sunt numite auxetice și se comportă destul de diferit de cele obișnuite. În loc să se stingă atunci când sunt stoarse, se prăbușesc în toate direcțiile, stocând energia din interior.
Posted: Aug 09, 2018
Scientists design material that can store energy like an eagle’s grip
(Nanowerk News) What do a flea and an eagle have in common? They can store energy in their feet without having to continuously contract their muscles to then jump high or hold on to prey. Now scientists at Queen Mary University of London and University of Cambridge have created materials that can store energy this way, be squeezed repeatedly without damage, and even change shape if necessary.
These kinds of materials are called auxetics and behave quite differently from regular materials. Instead of bulging out when squeezed, they collapse in all directions, storing the energy inside.
Current auxetic material designs have sharp corners which enable them to fold onto themselves, achieving higher density. This is a property that has been recognised recently in lightweight armour designs, where the material can collapse in front of a bullet upon impact. This is important because mass in front of a bullet is the biggest factor in armour effectiveness.
The sharp corners also concentrate forces and cause the material to fracture if squeezed multiple times, which is not a problem for armour as it is only designed to be used once.
In this study, published in Frontiers in Materials („Low Fatigue Dynamic Auxetic Lattices with 3D Printable, Multistable, and Tuneable Unit Cells”), the team of scientists redesigned the materials with smooth curves which distribute the forces and make repeated deformations possible for other applications where energy storing and shape-changing material properties are required.
The ratcheting building block that could be embedded in the new materials. After vertical compression, it keeps materials collapsed, and can release their energy on side-ways pull. (click on image to enlarge)
The work lays the basis for designs of lightweight 3D supports, which also fold in specific ways and store energy which could be released on demand.
Principle investigator Dr Stoyan Smoukov, from Queen Mary University of London, said: “The exciting future of new materials designs is that they can start replacing devices and robots. All the smart functionality is embedded in the material, for example the repeated ability to latch onto objects the way eagles latch onto prey, and keep a vice-like grip without spending any more force or effort.”
The team expects its nature-inspired designs could be used in energy-efficient gripping tools required in industry, re-configurable shape-on-demand materials, and even lattices with unique thermal expansion behaviour.
Eesha Khare, a visiting undergraduate student from Harvard University who was instrumental in defining the project, added: “A major problem for materials exposed to harsh conditions, such as high temperature, is their expansion. A material could now be designed so its expansion properties continuously vary to match a gradient of temperature farther and closer to a heat source. This way, it will be able to adjust itself naturally to repeated and severe changes.”
The flexible auxetic material designs, which were not possible before, were adapted specifically to be easily 3D-printed, a feature the authors consider essential.
Dr Smoukov added: “By growing things layer-by-layer from the bottom up, the possible material structures are mostly limited by imagination, and we can easily take advantage of inspirations we get from nature.”
În plus, au descoperit o modalitate de a adapta intensitatea și distribuția spațială a PMF pe grafen prin schimbarea unghiului de rotație dintre direcțiile cristalografice ale grafenului și BP. Atunci când se aplică un câmp magnetic extern în prezența PMF, aceștia pot să creeze două tipuri de curenți neechivalenți, cunoscuți drept curentul polarizat în vale în măsurătorile de transport electric.
Posted: Aug 08, 2018
Tailoring a large area pseudo-magnetic field in graphene by placing it on a crystal with different symmetry
The field of electronics focuses on how to control and exploit the properties of electrons. To study or modify the properties of these electrons at the quantum regime, a magnetic field has to be applied.
Another way of achieving this effect is to mechanically create a special type of strain in graphene, where the electrons behave as if they are under the influence of an externally applied magnetic field. In this case, no magnetic field is physically applied and this is explained by the presence of strain-induced PMF.
Electrons have additional degrees of freedom (independent parameter describing the electronic state) other than its charge. These are known as the spins and valley degree of freedom. Valleys are the maxima and minima of electron energies in a crystalline solid. A method to control electrons in different valleys can potentially be used to develop more efficient computing technologies.
Strain-induced PMFs in graphene have been explored as a promising approach to pull apart the valleys in graphene and make their energies non-equivalent, producing intriguing physics such as valley-polarised current. Many researchers have been attracted by the enormous PMFs (up to 300 teslas) observed in non-planar, strained graphene nanostructures such as graphene nanobubbles.
However, these are distributed randomly and they are not feasible for practical implementation. Although theory predicts that strains with triangular symmetry are able to create PMF in materials, there is currently no known experimental technique which can create the specific strain texture to generate a uniform PMF with the desired spatial distribution and intensity.
Figure 1: (Left) The lattice mismatch between the monolayer graphene (black) on multilayer black phosphorous (blue) generates PMF on the graphene layer. (Right) The spatial distribution and intensity of the PMF can be tailored by changing the rotation angle between the graphene and black phosphorous. (Image: NUS)
A team led by Prof LOH Kian Ping from the Department of Chemistry and Centre for Advanced 2D Materials, NUS has discovered a way to generate PMFs on graphene by overlaying graphene on black phosphorous (BP) to form a graphene-on-BP heterostructure (Figure 1). The research team also includes surface chemist Prof LU Jiong and theoretician Prof Adam SHAFFIQUE from NUS. The large lattice mismatch and shear strain imposed by the lattices on each other give rise to PMFs on graphene, which can be measured directly using scanning tunnelling microscopy (Figure 2).
Figure 2: Moiré superlattices (left panel) formed by the graphene-on-black phosphorus heterostructure as measured by a scanning tunnelling microscope and its corresponding PMF map (right panel). (Image: NUS)
In addition, they discovered a way to tailor the intensity and spatial distribution of the PMFs on graphene by changing the rotation angle between the crystallographic directions of the graphene and the BP. When an external magnetic field is applied in the presence of the PMF, they are able to create two types of non-equivalent currents, known as the valley-polarised current in electrical transport measurements.
Prof Loh said, “Controlling PMFs at the nanoscale allows the following extreme physics to be tested: first, the PMF fields can serve as energy barriers to efficiently confine currents into a one-dimensional channel. In addition, valley filters can be developed based on valley polarisation. Importantly, we discovered that a complex strain texture formed by placing a hexagonal crystal (graphene) on an orthorhombic crystal (BP) is suitable for generating a large area PMF.
The implication is that there might be other combinations of two-dimensional crystals which have not been discovered yet. Our study thus opens up new opportunities for strain engineering with a view towards tailoring the spatial distribution and intensity of the PMFs.”
O echipă de cercetători de la Universitatea din Kiel (CAU) a reușit în mod semnificativ să mărească semnificativ efectul adeziv al unui material siliconic. Pentru a face acest lucru, au combinat două metode: în primul rând, au structurat suprafața pe scară micro pe baza exemplului picioarelor de gândac și apoi au tratat-o cu plasmă. În plus, au descoperit că aderența materialului structurat se modifică drastic, dacă este îndoit în grade diferite.
Posted: Aug 08, 2018
High-tech adhesives inspired by feet
(Nanowerk News) Geckos, spiders and beetles have shown us how to do it: thanks to special adhesive elements on their feet, they can easily run along ceilings or walls. The science of bionics tries to imitate and control such biological functions, for technological applications and the creation of artificial materials.
A research team from Kiel University (CAU) has now succeeded in boosting the adhesive effect of a silicone material significantly. To do so they combined two methods: First, they structured the surface on the micro scale based on the example of beetle feet, and thereafter treated it with plasma. In addition, they found out that the adhesiveness of the structured material changes drastically, if it is bent to varying degrees.
Different configurations change the adhesive effect of the silicone material, whose surface has been given a mushroom-like structure. (Image: Emre Kizilkan)
Elastic synthetic materials such as silicone elastomers are very popular in industry. They are flexible, re-usable, cheap and easy to produce. They are therefore used for example as seals, for insulation or as corrosion protection. However, due to their low surface energy, they are hardly adhesive at all. This makes it difficult, for example, to paint silicone surfaces.
Surfaces with a mushroom-like microstructure adhere much better
Professor Stanislav N. Gorb and Emre Kizilkan from the Functional Morphology and Biomechanics working group are researching how to improve the adhesive properties of silicone elastomers. Their example to mimic is the surface structure of certain male leaf beetles (Chrysomelidae), looking like mushrooms.
In two recent studies, they discovered that silicone elastomers adhere best if their surface is modified into mushroom-like structures and thereafter specifically treated with plasma. The electrically-charged gas which is the fourth state of matter, alongside solids, liquids and gases. Thus, the researchers combined a geometrical and a chemical method, to imitate biology. In addition, they showed that the degree of curvature of the materials affects their adhesion.
„Animals and plants provide us with a wealth of experience about some incredible features. We want to transfer the mechanisms behind them to artificial materials, to be able to control their behaviour in a targeted manner,” said the zoologist Gorb. Their goal of a reversible adhesion in the micro range without traditional glue could make completely new application possibilities conceivable – for example in micro-electronics.
During experimental tests silicones are curved
In a first step, the research team compared silicone elastomers of three different surfaces: one unstructured, one with pillar-shaped elements and a third with a mushroom-like structure. Using a micro-manipulator, they stuck a glass ball onto the surfaces and then removed it again. They tested how the adhesion changes when the materials with microstructured surfaces are bent convex (inwards) and concave (outwards).
Silicone surfaces treated with plasma (below) have stronger adhesiveness than untreated surfaces (above). (Image: Emre Kizilkan)
„In this way, we were able to demonstrate that silicone materials with a mushroom-like structure and curved concave have the double range of adhesive strength,” said doctoral researcher Emre Kizilkan, first author of the study. „With this surface structure, we can vary and control the adhesion of materials the most.”
Exact parameters for material-friendly plasma treatment
In a second step, the scientists treated the silicone elastomers with plasmas. This method is normally used to functionalise plastic materials, in order to increase their surface energy and to improve their adhesive properties. In comparison with other methods using liquids, plasma treatments can promise greater longevity – however, they often damage the surfaces of materials.
To find out how plasma treatments can significantly improve the adhesion of a material without damaging it, the scientists varied different parameters, such as the duration or the pressure. They found that the adhesion of unstructured surfaces on a glass substrate increased by approximately 30% after plasma treatment. On the mushroom-like structured surface the adhesion even increased by up to 91%.
„These findings particularly surprised us, because the structured surface is only half as large as the unstructured, but adhesion enhancement was even three times better after the plasma treatment,” explained Kizilkan.
What happens when the treated and non-treated structured surfaces are removed from the glass substrate show the recordings with a high-speed camera: Because of its higher surface energy the plasma-treated microstructure remains fully in contact with the surface of the glass for 50,6 seconds. However, the contact area of the untreated microstructure is reduced quickly by around one third during the removal process, which is why the microstructure completely detaches from the glass substrate after 33 seconds already (Figure 3).
Especially suitable for applications in microelectronics
„We therefore have on a very small area an extremely strong adhesion with a wide range,” summarizes the material scientist Kizilkan. This makes the results especially interesting for small-scale applications such as micro-robots. The findings of the Kiel working group have already resulted in the development of an extremely strong adhesive tape, which functions according to the „gecko principle”, and can be removed without leaving any residue.
The studies were conducted within the framework of the Collaborative Research Centre 677 „Function by Switching” at Kiel University.
Bateriile viitorului pot fi făcute din hârtie. Cercetătorii de la Universitatea Binghamton, Universitatea de Stat din New York, au creat o baterie biodegradabilă, pe bază de hârtie, care este mai eficientă decât era posibil anterior.anterior”.
Biobatteria folosește un hibrid de polimeri de hârtie și de inginerie. Polimerii – acidul poli (amic) și poli (dianhidrida piromelit-p-fenilendiamină) – au fost cheia pentru a da proprietăților biodegradabile ale bateriilor.
(Nanowerk News) The batteries of the future may be made out of paper. Researchers at Binghamton University, State University at New York have created a biodegradable, paper-based battery that is more efficient than previously possible (Advanced Sustainable Systems, „Green Biobatteries: Hybrid Paper–Polymer Microbial Fuel Cells”).
Researchers at Binghamton University, State University at New York have created a biodegradable, paper-based battery that is more efficient than previously possible. (Image: Seokheun “Sean” Choi)
For years, there has been excitement in the scientific community about the possibility of paper-based batteries as an eco-friendly alternative. However, the proposed designs were never quite powerful enough, they were difficult to produce and it was questionable whether they were really biodegradable.
This new design solves all of those problems.
Associate Professor Seokheun “Sean” Choi from the Electrical and Computer Engineering Department and Professor Omowunmi Sadik from the Chemistry Department worked on the project together. Choi engineered the design of the paper-based battery, while Sadik was able to make the battery a self-sustaining biobattery.
“There’s been a dramatic increase in electronic waste and this may be an excellent way to start reducing that,” said Choi. “Our hybrid paper battery exhibited a much higher power-to-cost ratio than all previously reported paper-based microbial batteries.”
The biobattery uses a hybrid of paper and engineered polymers. The polymers – poly (amic) acid and poly (pyromellitic dianhydride-p-phenylenediamine) – were the key to giving the batteries biodegrading properties.
The team tested the degradation of the battery in water and it clearly biodegraded without the requirements of special facilities, conditions or introduction of other microorganisms.
The polymer-paper structures are lightweight, low-cost and flexible. Choi said that flexibility also provides another benefit.
“Power enhancement can be potentially achieved by simply folding or stacking the hybrid, flexible paper-polymer devices,” said Choi.
The team said that producing the biobatteries is a fairly straightforward process and that the material allows for modifications depending on what configuration is needed.
