Large Nanotube Sheets
16 January 2012, 19:32
Categories: nanotubes-wires-fullerenes
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Nanotubes are among the strongest and most conductive materials known. For decades, researchers have dreamed of using them to make super-efficient electrical transmission lines, suspension bridges that can span several kilometers, and even elevators that convey satellites into space.
But while some companies have succeeded in making useful products by mixing nanotubes with resins to create composites, it’s been difficult to make materials with properties that reflect those of the individual nanotubes. Now, by making large sheets composed of nanotubes alone, Nanocomp Technologies has taken a big step in that direction.
The sheets are still not as strong or conductive as individual nanotubes, but they can provide a lighter replacement for copper and other conventional materials in some applications, including protective shielding for coaxial cables.
The nanotubes are made by feeding alcohol and a catalyst into a furnace at high temperatures and pressures. Nanocomp has fine-tuned the process to produce relatively long nanotubes that emerge from the furnace to form networks that can serve as the basis for sheets.
Nanocomp’s first customers are NASA, which has used nanotube sheets to shield a deep-space probe from radiation, and the U.S. military, which could use the sheets to reduce the weight of the electrical cables on unmanned drones by half, increasing flight times.
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Twelve Atom Storage Device
16 January 2012, 19:22
Categories: molecular-machines--devices
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Researchers at I.B.M. have stored and retrieved binary data from an array of just 12 atoms, pushing the boundaries of the magnetic storage of information to the edge of what is possible. The findings could help lead to a new class of nanomaterials for a generation of memory chips and disk drives that will not only have greater capabilities than the current silicon-based computers but will consume significantly less power. And they may offer a new direction for research in quantum computing.
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Happy New Year!
1 January 2012, 00:00
Categories: other
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Painting Solar Cells With Nanoparticle Paste
31 December 2011, 14:55
Categories: smt-energy-photovoltaic nanoparticles
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Researchers at Notre Dame have developed a solar cell that is remarkably easy to assemble because the middle layer can be painted onto a clear electrode. First, they mix t-butanol, water, cadmium sulfide and titanium dioxide for 30 minutes. Next, they mask off a clear electrode with office tape. Once the tape is in place, they spread the mixture onto the electode and then anneal it with a heat gun. Finally, they sandwich an electrolyte solution between the new electrode and a graphene composite electrode. And then, it’s time for testing under a beam of artificial light.
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Holographic 3-D Displays
31 December 2011, 14:30
Categories: nano-emissive-displays NEMS--MEMS
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Applications like holographic TV have long been relegated as the next big thing in the distant future but a Belgium-based R&D lab for nanoelectronics has come up with a process that might bring holographic images closer to realtime.
At Imec, their work involves creating moving pixels. They are constructing holographic displays by shining lasers on microelectromechanical systems (MEMS) platforms that can move up and down like small, reflective pistons.
“Holographic visualization promises to offer a natural 3-D experience for multiple viewers, without the undesirable side-effects of current 3D stereoscopic visualization (uncomfortable glasses, strained eyes, fatiguing experience),” the company states.
In their nanoscale system, they work with chips made by growing a layer of silicon oxide on to silicon wafer. They etch square patches of the silicon oxide. The result is a checkerboard-like pattern where etched-away pixels are nanometers lower than their neighbors. A reflective aluminum coating tops the chip. When laser light shines on the chip, it bounces off of the boundary between adjacent pixels at an angle.
Diffracted light interferes constructively and destructively to create a 3-D picture where small mirrored platforms are moving up and down, many times a second, to create a moving projection. The process can also be described as the pixels closer to the light interfering with it one way and those further off, in another. The small distances between them generate the image that the eye sees.
Imec hopes to construct the first, proof-of-concept moving structures by mid-2012. “Imec’s vision is to design the ultimate 3D display: a holographic display with a 60° diffraction angle and a high-definition visual experience,” they state.
As such, Imec will have lots of company elsewhere in the race to iron out complexities of holographic imaging. According to reports throughout 2011, research teams aim to make the technology more of a reality than a wish-list item for consumers.
The BBC R&D department has identified the work that broadcasters are doing across Europe, for example, in holographic TV. Engineers are also focused on research into 3-D holoscopy for the Internet and other 3-D applications.
Researchers at MIT this year said they were closing in on holographic TV by building a system with a refresh rate of 15 frames per second. Also earlier this year, the Defense Advanced Research Projects Agency (DARPA) completed a five-year project called Urban Photonic Sandtable Display that creates realtime, color, 360-degree 3-D holographic displays.
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An Eco-Friendly Alternative To Cement
31 December 2011, 14:11
Categories: nanotubes-wires-fullerenes nanocomposites
Researchers at the University of Alabama and Auburn University are working on a solution to environmental problems by finding an alternative to the use of cement in concrete, by developing an inexpensive and eco-friendly material consisting of fly ash and carbon nanotubes. While the material is like cement, it eliminates many environmental issues of cement use.
Fly ash is a fine powder derived from burning coal. Use of these coal waste products conserves space in landfills, in which they would otherwise be dumped. Fly ash has been used to make concrete and , because fly ash displaces the use of cement, it eliminates the main disadvantages of cement: greenhouse gas emissions, deterioration, non-recyclability, and radon exhalation.
The three-year study is focused on perfecting fly-ash materials and developing methods for large-scale production. Fly-ash materials tend to be strong with compression, but brittle with tension. To combat this issue, the team is experimenting with adding carbon nanotubes to the fly ash.
The carbon nanotubes (CNTs) are spun into long, thin fibers, like yarn, that are tougher and stronger than steel. Adding CNTs to the fly ash not only strengthens the material, but it also makes it multifunctional. In addition, CNTs are excellent electrical and thermal conductors. By adding CNTs, fly ash materials become electrically conductive. Electric conductivity can be used to enhance melting ice on structures, such as bridges and airport runways, eliminating possible winter hazards.
The conductivity also changes with applied force. As applied force changes, the electric resistance changes. A change in conductivity often indicates damage or increased load to a material. Therefore, testing the electric resistance of the fly ash materials reinforced with CNTs is a simple way to determine if there is any damage to a structure.
Dr. Jialai Wang said CNT’s can “sense” structural damage, a function called “self-sensing.”
“Civil structures are just like the human body,” Wang said. “They can be ‘sick.’ If no action is taken, there can be serious consequences. Materials with self-sensing abilities can let you know promptly where there is a problem in a structure and catastrophic failure, like the collapse of a bridge, can be avoided.”
Wang has received a patent for the technology he developed to combine CNTs with fly ash. The nanotube technology, nicknamed “Pop Tube Technology,” uses microwave radiation to initiate nanotube formation. The microwaves cause nanotubes to pop out, like popcorn. The PopTube technology has many advantages compared to existing methods. It requires very simple equipment, can be easily scaled up for large-scale manufacture and is highly energy-efficient and cost-effective.
The goal of this study is to garner information valuable for further studies in eco-friendly and durable materials. Such materials would have significant social, economic and environmental benefits for the construction industry.
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Dark Quantum Shadows Increase Solar Cell Efficiency
31 December 2011, 13:39
Categories: quantum-mechanics smt-energy-photovoltaic
Researchers at The University of Texas at Austin have discovered that it’s possible to double the number of electrons harvested from one photon of sunlight using an organic plastic semiconductor material.
“Plastic semiconductor solar cell production has great advantages, one of which is low cost,” said Xiaoyang Zhu. “Combined with the vast capabilities for molecular design and synthesis, our discovery opens the door to an exciting new approach for solar energy conversion, leading to much higher efficiencies.”
The maximum theoretical efficiency of the silicon solar cell in use today is approximately 31 percent, because much of the sun’s energy hitting the cell is too high to be turned into usable electricity. That energy, in the form of “hot electrons,” is instead lost as heat. Capturing hot electrons could potentially increase the efficiency of solar-to-electric power conversion to as high as 66 percent.
Zhu and his team previously demonstrated that those hot electrons could be captured using semiconductor nanocrystals. They published that research in Science in 2010, but Zhu says the actual implementation of a viable technology based on that research is very challenging.
“For one thing,” said Zhu, “that 66 percent efficiency can only be achieved when highly focused sunlight is used, not just the raw sunlight that typically hits a solar panel. This creates problems when considering engineering a new material or device.”
To circumvent that problem, Zhu and his team have found an alternative. They discovered that a photon produces a dark quantum “shadow state” from which two electrons can then be efficiently captured to generate more energy in the semiconductor pentacene.
Zhu said that exploiting that mechanism could increase solar cell efficiency to 44 percent without the need for focusing a solar beam, which would encourage more widespread use of solar technology.
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A Decade Of NanoRisk Research
31 December 2011, 13:11
Categories: responsible-nanotechnology
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A 60 page report recently published by the German Society for Chemical Engineering and Biotechnology (DECHEMA) and the Chemical Industry Association (VCI), titled “10 Jahre Forschung zu Risikobewertung, Human- und Ökotoxikologie von Nanomaterialien” (PDF), offers an overview of research projects conducted during the last decade on the subject of nanosafety. It covers six Swiss, 40 German, one US and 25 EU projects.
In another report, titled “Impact of engineered nanomaterials on health: considerations for benefit-risk assessment” (LINK), the European Academies Science Advisory Council (EASAC) drew attention to the gaps in our scientific knowledge in this field and indicated very clearly the topics which need to be researched in the coming years in order that nanomaterials can be directly utilized without risks to our environment or to human health.
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Graphene Oxide Controls Fluid Pressure By Plugging Pores
31 December 2011, 12:23
Categories: smt-rheometry-smart-fluids nanotubes-wires-fullerenes
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Graphene’s star is rising as a material that could become essential to efficient, environmentally sound oil production. Rice University researchers are taking advantage of graphene’s outstanding strength, light weight and solubility to enhance fluids used to drill oil wells.
The Rice University lab of chemist James Tour and scientists at M-I SWACO, a Texas-based supplier of drilling fluids and subsidiary of oil-services provider Schlumberger, have produced functionalized graphene oxide to alleviate the clogging of oil-producing pores in newly drilled wells.
Rice’s relationship with M-I SWACO began more than two years ago when the company funded the lab’s follow-up to research that produced the first graphene additives for drilling fluids known as muds. These fluids are pumped downhole as part of the process to keep drill bits clean and remove cuttings. With traditional clay-enhanced muds, differential pressure forms a layer on the wellbore called a filter cake, which both keeps the oil from flowing out and drilling fluids from invading the tiny, oil-producing pores.
When the drill bit is removed and drilling fluid displaced, the formation oil forces remnants of the filter cake out of the pores as the well begins to produce. But sometimes the clay won’t budge, and the well’s productivity is reduced.
The Tour Group discovered that microscopic, pliable flakes of graphene can form a thinner, lighter filter cake. When they encounter a pore, the flakes fold in upon themselves and look something like starfish sucked into a hole. But when well pressure is relieved, the flakes are pushed back out by the oil.
All that was known two years ago. Since then, Tour and a research team led by Dmitry Kosynkin, a former Rice postdoctoral associate and now a petroleum engineer at Saudi Aramco, have been fine-tuning the materials.
They found a few issues that needed to be dealt with. First, pristine graphene is hard to disperse in water, so it is unsuitable for water-based muds. Graphene oxide (GO) turned out to be much more soluble in fresh water, but tended to coagulate in saltwater, the basis for many muds.
The solution was to “esterify” GO flakes with alcohol. “It’s a simple, one-step reaction,” said Tour, Rice’s T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science. “Graphene oxide functionalized with alcohol works much better because it doesn’t precipitate in the presence of salts. There’s nothing exotic about it.”
In a series of standard American Petroleum Institute tests, the team found the best mix of functionalized GO to be a combination of large flakes and powdered GO for reinforcement. A mud with 2 percent functionalized GO formed a filter cake an average of 22 micrometers wide — substantially smaller than the 278-micrometer cake formed by traditional muds. GO blocked pores many times smaller than the flakes’ original diameter by folding.
Aside from making the filter cake much thinner, which would give a drill bit more room to turn, the Rice mud contained less than half as many suspended solids; this would also make drilling more efficient as well as more environmentally friendly. Tour and Andreas Lüttge, a Rice professor of Earth science and chemistry, reported last year that GO is reduced to graphite, the material found in pencil lead and a natural mineral, by common bacteria.
“The most exciting aspect is the ability to modify the GO nanoparticle with a variety of functionalities,” said James Friedheim, corporate director of fluids research and development at M-I SWACO and a co-author of the research. “Therefore we can ‘dial in’ our application by picking the right organic chemistry that will suit the purpose. The trick is just choosing the right chemistry for the right purpose.”
“There’s still a lot to be worked out,” Tour said. “We’re looking at the rheological properties, the changes in viscosity under shear. In other words, we want to know how viscous this becomes as it goes through a drill head, because that also has implications for efficiency.”
Muds may help graphene live up to its commercial promise, Tour said. “Everybody thinks of graphene in electronics or in composites, but this would be a use for large amounts of graphene, and it could happen soon,” he said.
Friedheim agreed. “With the team we currently have assembled, Jim Tour’s group and some development scientists at M-I SWACO, I am confident that we are close to both technical and commercial success.”
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Ordinary Sunlight Cleans Fabric, With Light In The Visible Range
31 December 2011, 10:54
Categories: nanoparticles self-cleaning
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Imagine jeans, sweats or socks that clean and de-odorize themselves when hung on a clothesline in the sun or draped on a balcony railing. Scientists from Hubei University for Nationalities and Shanghai Jiao Tong University, both in China, are reporting development of a new cotton fabric that does clean itself of stains and bacteria when exposed to ordinary sunlight.
Self-cleaning cotton fabrics have been made in the past, the authors note, but they self-clean thoroughly only when exposed to ultraviolet rays. So they set out to develop a new cotton fabric that cleans itself when exposed to ordinary sunlight.
Mingce Long and Deyong Wu say their fabric uses a coating made from a compound of titanium dioxide, the white material used in everything from white paint to foods to sunscreen lotions. The titanium dioxide breaks down dirt and kills microbes when exposed to some types of light. It already has found uses in self-cleaning windows, kitchen and bathroom tiles, odor-free socks and other products.
Their report describes a cotton fabric coated with AgI nanoparticles made from a compound of titanium dioxide and nitrogen. They show that the AgI–N–TiO2–cotton material removes an orange dye stain when exposed to sunlight. Further dispersing nanoparticles composed of silver and iodine accelerates the discoloration process. The coating remains intact after washing and drying.
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Porous Nanocoating For Smart Windows
31 December 2011, 09:04
Categories: coatings smart-materials-smt
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Vanadium dioxide (VO2) has long been recognized as a a material of significant technological interest for optics and electronics, and as a promising candidate for making smart windows; it can transition from a transparent semiconductive state at low temperatures, allowing infrared radiation through, to an opaque metallic state at high temperatures, while still allowing visible light to get through. VO2 is best known in the materials world for its speedy and abrupt phase transition that essentially transforms the material from a metal to an insulator. The phase change takes place at about 68 degrees Celsius.
So far, VO2 hasn’t been considered to be particularly suited for large-scale practical smart-window applications due to its low luminous transmittance and solar modulating ability. Strategies to improve these properties, for instance through doping or composites, have resulted in trade-offs between the luminous transmittance and thermochromic properties.
Researchers at the Shanghai Institute of Ceramics, Chinese Academy of Sciences (SICCAS), have now developed a process that can prepare VO2 thin-films with a controllable polymorph and morphology (including grain size and porosity). Their results show that with increased porosity and decreased optical constants the performance of the VO2 films is enhanced, leading to a higher transmittance of visible light and improved solar modulating ability.
“The traditional methods for the preparation of VO2 thin films are gas-phase reactions, such as sputtering or chemical vapor deposition,” says Yanfeng Gao. “These methods can grow VO2 with fine controlled thickness and homogeneity, however, low visible transmittance due to intrinsic absorption of VO2 and unacceptable solar energy modulation ability pose significant drawbacks. There are only very few reports on the chemical deposition of VO2 films using – for example – sol-gel process, but the quality of film is still not satisfactory. We are aiming to develop a process that can finally commercialize VO2. We selected our method to control the crystalline phase and morphology, and also optical properties.”
Experimenting with various thicknesses, the team found that the optimized thickness for films prepared by their technique to balance luminous transmittance and solar modulating ability is 100 nm. As Gao points out, a single-layer film of this thickness shows comparable luminous transmittance and solar modulating ability values to those of five-layered TiO2/VO2/TiO2/VO2/TiO2 films with optically optimized structures.
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Sketching Electronics
30 December 2011, 15:50
Categories: coatings artists
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Leah Buechley is an assistant professor at the MIT Media Lab and the director of the High-Low Tech research group. This is her latest video, which shows off a kit for “sketching” electronics. Buechley is using a conductive ink pen that was developed by the Lewis Lab at the University of Illinois at Urbana-Champaign.
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Self-Healing Electronics Could Work Longer And Reduce Waste
30 December 2011, 14:51
Categories: nanocomposites biomimicry
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When one tiny circuit within an integrated chip cracks or fails, the whole chip – or even the whole device – is a loss. But what if it could fix itself, and fix itself so fast that the user never knew there was a problem?
A team of University of Illinois engineers has developed a self-healing system that restores electrical conductivity to a cracked circuit in less time than it takes to blink. Led by aerospace engineering professor Scott White and materials science and engineering professor Nancy Sottos, the researchers published their results in the journal Advanced Materials.
“It simplifies the system,” said chemistry professor Jeffrey Moore, a co-author of the paper. “Rather than having to build in redundancies or to build in a sensory diagnostics system, this material is designed to take care of the problem itself.”
As electronic devices are evolving to perform more sophisticated tasks, manufacturers are packing as much density onto a chip as possible. However, such density compounds reliability problems, such as failure stemming from fluctuating temperature cycles as the device operates or fatigue. A failure at any point in the circuit can shut down the whole device.
“In general there’s not much avenue for manual repair,” Sottos said. “Sometimes you just can’t get to the inside. In a multilayer integrated circuit, there’s no opening it up. Normally you just replace the whole chip. It’s true for a battery too. You can’t pull a battery apart and try to find the source of the failure.”
Most consumer devices are meant to be replaced with some frequency, adding to electronic waste issues, but in many important applications – such as instruments or vehicles for space or military functions – electrical failures cannot be replaced or repaired.
The Illinois team previously developed a system for self-healing polymer materials and decided to adapt their technique for conductive systems. They dispersed tiny microcapsules, as small as 10 microns in diameter, on top of a gold line functioning as a circuit. As a crack propagates, the microcapsules break open and release the liquid metal contained inside. The liquid metal fills in the gap in the circuit, restoring electrical flow.
“What’s really cool about this paper is it’s the first example of taking the microcapsule-based healing approach and applying it to a new function,” White said. “Everything prior to this has been on structural repair. This is on conductivity restoration. It shows the concept translates to other things as well.”
A failure interrupts current for mere microseconds as the liquid metal immediately fills the crack. The researchers demonstrated that 90 percent of their samples healed to 99 percent of original conductivity, even with a small amount of microcapsules.
The self-healing system also has the advantages of being localized and autonomous. Only the microcapsules that a crack intercepts are opened, so repair only takes place at the point of damage. Furthermore, it requires no human intervention or diagnostics, a boon for applications where accessing a break for repair is impossible, such as a battery, or finding the source of a failure is difficult, such as an air- or spacecraft.
“In an aircraft, especially a defense-based aircraft, there are miles and miles of conductive wire,” Sottos said. “You don’t often know where the break occurs. The autonomous part is nice – it knows where it broke, even if we don’t.”
Next, the researchers plan to further refine their system and explore other possibilities for using microcapsules to control conductivity. They are particularly interested in applying the microcapsule-based self-healing system to batteries, improving their safety and longevity.
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Large Sheets Of Carbon Nanotubes
30 December 2011, 14:29
Categories: nanotubes-wires-fullerenes
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Nanocomp Technologies is turning carbon nanotubes into paper-thin sheets many meters long. The work is important because, while some companies have succeeded in making useful products by mixing nanotubes with resins to create composites, it’s been difficult to make materials with properties that reflect those of the individual nanotubes. By making large sheets composed of nanotubes alone, Nanocomp has taken a big step in that direction.
The sheets are still not as strong or conductive as individual nanotubes, but they can provide a lighter replacement for copper and other conventional materials in some applications, including protective shielding for coaxial cables. Nanocomp’s first customers are NASA, which has used nanotube sheets to shield a deep-space probe from radiation, and the U.S. military, which could use the sheets to reduce the weight of the electrical cables on unmanned drones by half, increasing flight times.
The nanotubes are made by feeding alcohol and a catalyst into a furnace at high temperatures and pressures. Nanocomp has fine-tuned the process to produce relatively long nanotubes that emerge from the furnace to form networks that can serve as the basis for sheets.
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Nanohairs Inhibit Biofilm Growth
30 December 2011, 14:12
Categories: bionanotech--nanobiotech self-cleaning
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Bacteria that contaminate systems ranging from medical implants to industrial pipelines are tough to eradicate once they attach to such surfaces as slimy “biofilms”. The conventional countermeasure of surface chemistry treatments only works for a number of hours, as secreted proteins and small molecules quickly mask the treated surface and re-enable colonization.
Taking a radically different approach, researchers at Harvard University and the Wyss Institute for Biologically Inspired Engineering have designed biofilm-inhibiting surfaces that rely only on nanoscale geometric and mechanical factors to reduce bacterial attachment. The work brings together two recent findings: (1) bacteria can be artificially and arbitrarily patterned as they attach to a surface that presents an array of nanoposts; and (2) bacteria decide to attach to materials based in part on mechanical stiffness, preferring stiffer substrates.
To determine the parameters of a nanopost array that drive bacterial patterning, the scientists tested asymmetric and combinatorial nanopost array surfaces with gradients of geometry. They found that the spacing between neighbouring nanoposts was key to bacterial insertion between posts and to maximizing cell contact with the array.
Next, the team asked: if bacteria can sense the stiffness of a flat surface, why not the effective stiffness of a soft “hairy” surface? Could the cells be tricked into perceiving the surface as being “too soft” to colonize?
Indeed, the group found that below a threshold effective stiffness, a super-flexible nanopost array significantly decreased bacterial attachment to a polymer surface compared with flat surfaces made from the same material. This was true even beyond 24 hours of incubation.
Surfaces with nanoarrays that induce bacterial patterning as well as effectively emulate a super-soft surface could be a new, longer-lasting way to control biofilm growth and consequently reduce biofilm-borne infections and damage. What’s more, such a “hairy” nanoarray could be cast or imprinted as part of the base material for one-step manufacturing of biofilm-resistant equipment.
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Humans Inspire Touchy Materials
30 December 2011, 11:32
Categories: biomimicry sensors
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When we rub a finger across a surface, our sense of touch is remarkably adept at distinguishing between different textures1. For example, astute clothes shoppers can easily feel the difference in texture between cotton and lower quality polyester fabrics, just as experienced cashiers can spot counterfeit banknotes from the feel of the paper.
Writing in Physical Review Letters, researcher from UPMC Université Paris have provided a major advance towards understanding the physics behind these tactile sensations, showing how a modulated frictional signal is generated by fingerprint-like ridges rubbing against the roughness of an opposing surface.
This improved understanding of the relationship between friction and surface textures should have an impact in many areas, but particularly in the field of tactile sensors for robotic design. Incorporating sensors capable of mimicking the human sense of touch has long been recognized as important for improving the ability of robots to grasp objects firmly without damaging them.
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Corkscrew Molecules Kill Infectious Organisms
30 December 2011, 11:11
Categories: biomimicry bionanotech--nanobiotech
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Scientists at the University of Warwick in the UK have taken inspiration from corkscrew structures found in nature to develop a new weapon in the fight against infections like E. coli and MRSA.
Researchers have created a new synthetic class of helix-shaped molecules which they believe could be a key tool in the worldwide battle against antibiotic resistance. By twisting molecules around iron atoms they have created what they term ‘flexicates’ which are active against MRSA and E. coli – but which also appear to have low toxicity, reducing the potential for side effects if used in treatment. The work is published in Nature Chemistry.
The new structures harness the phenomenon of ‘chirality’ or ‘handedness’ whereby the corkscrew molecules could be left-handed or right-handed. By making the most effective ‘hand’ to attack a specific disease, the University of Warwick research paves the way towards a more targeted approach to killing pathogens. In the case of E. coli and MRSA, it is the left ‘hand’ which is most effective.
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Graphene Foam Detects Explosives & Emissions Better
30 December 2011, 10:56
Categories: gels--foams sensors
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A new study by researchers from Rensselaer Polytechnic Institute and the Chinese Academy of Sciences demonstrates how graphene foam can outperform leading commercial gas sensors in detecting potentially dangerous and explosive chemicals. The discovery opens the door for a new generation of gas sensors to be used by bomb squads, law enforcement officials, defense organizations, and in various industrial settings.
The new sensor successfully and repeatedly measured ammonia (NH3) and nitrogen dioxide (NO2) at concentrations as small as 20 parts-per-million. Made from continuous graphene nanosheets that grow into a foam-like structure about the size of a postage stamp and thickness of felt, the sensor is flexible, rugged, and finally overcomes the shortcomings that have prevented nanostructure-based gas detectors from reaching the marketplace.
Results of the study were published in the journal Scientific Reports, published by Nature Publishing Group: High Sensitivity Gas Detection Using a Macroscopic Three-Dimensional Graphene Foam Network.
“We are very excited about this new discovery, which we think could lead to new commercial gas sensors,” said Rensselaer Engineering Professor Nikhil Koratkar, who co-led the study along with Professor Hui-Ming Cheng at the Shenyang National Laboratory for Materials Science at the Chinese Academy of Sciences. “So far, the sensors have shown to be significantly more sensitive at detecting ammonia and nitrogen dioxide at room temperature than the commercial gas detectors on the market today.”
Over the past decade researchers have shown that individual nanostructures are extremely sensitive to chemicals and different gases. To build and operate a device using an individual nanostructure for gas detection, however, has proven to be far too complex, expensive, and unreliable to be commercially viable, Koratkar said. Such an endeavor would involve creating and manipulating the position of the individual nanostructure, locating it using microscopy, using lithography to apply gold contacts, followed by other slow, costly steps. Embedded within a handheld device, such a single nanostructure can be easily damaged and rendered inoperable. Additionally, it can be challenging to “clean” the detected gas from the single nanostructure.
The new postage stamp-sized structure developed by Koratkar has all of the same attractive properties as an individual nanostructure, but is much easier to work with because of its large, macroscale size. Koratkar’s collaborators at the Chinese Academy of Sciences grew graphene on a structure of nickel foam. After removing the nickel foam, what’s left is a large, free-standing network of foam-like graphene. Essentially a single layer of the graphite found commonly in our pencils or the charcoal we burn on our barbeques, graphene is an atom-thick sheet of carbon atoms arranged like a nanoscale chicken-wire fence. The walls of the foam-like graphene sensor are comprised of continuous graphene sheets without any physical breaks or interfaces between the sheets.
Koratkar and his students developed the idea to use this graphene foam structure as a gas detector. As a result of exposing the graphene foam to air contaminated with trace amounts of ammonia or nitrogen dioxide, the researchers found that the gas particles stuck, or adsorbed, to the foam’s surface. This change in surface chemistry has a distinct impact upon the electrical resistance of the graphene. Measuring this change in resistance is the mechanism by which the sensor can detect different gases.
Additionally, the graphene foam gas detector is very convenient to clean. By applying a ~100 milliampere current through the graphene structure, Koratkar’s team was able to heat the graphene foam enough to unattach, or desorb, all of the adsorbed gas particles. This cleaning mechanism has no impact on the graphene foam’s ability to detect gases, which means the detection process is fully reversible and a device based on this new technology would be low power—no need for external heaters to clean the foam—and reusable.
Koratkar chose ammonia as a test gas to demonstrate the proof-of-concept for this new detector. Ammonium nitrate is present in many explosives and is known to gradually decompose and release trace amounts of ammonia. As a result, ammonia detectors are often used to test for the presence of an explosive. A toxic gas, ammonia also is used in a variety of industrial and medical processes, for which detectors are necessary to monitor for leaks.
Results of the study show the new graphene foam structure detected ammonia at 1,000 parts-per-million in 5 to 10 minutes at room temperature and atmospheric pressure. The accompanying change in the graphene’s electrical resistance was about 30 percent. This compared favorably to commercially available conducting polymer sensors, which undergo a 30 percent resistance change in 5 to 10 minutes when exposed to 10,000 parts-per-million of ammonia. In the same time frame and with the same change in resistance, the graphene foam detector was 10 times as sensitive. The graphene foam detector’s sensitivity is effective down to 20 parts-per-million, much lower than the commercially available devices. Additionally, many of the commercially available devices require high power consumption since they provide adequate sensitivity only at high temperatures, whereas the graphene foam detector operates at room temperature.
Koratkar’s team used nitrogen dioxide as the second test gas. Different explosives including nitrocellulose gradually degrade, and are known to produce nitrogen dioxide gas as a byproduct. As a result, nitrogen dioxide also is used as a marker when testing for explosives. Additionally, nitrogen dioxide is a common pollutant found in combustion and auto emissions. Many different environmental monitoring systems feature real-time nitrogen dioxide detection.
The new graphene foam sensor detected nitrogen dioxide at 100 parts-per-million by a 10 percent resistance change in 5 to 10 minutes at room temperature and atmospheric pressure. It showed to be 10 times more sensitive than commercial conducting polymer sensors, which typically detect nitrogen dioxide at 1,000 part-per-million in the same time and with the same resistance chance at room temperature. Other nitrogen dioxide detectors available today require high power consumption and high temperatures to provide adequate sensitivity. The graphene foam sensor can detect nitrogen dioxide down to 20 parts-per-million at room temperature.
“We see this as the first practical nanostructure-based gas detector that’s viable for commercialization,” said Koratkar, a professor in the Department of Mechanical, Aerospace, and Nuclear Engineering at Rensselaer. “Our results show the graphene foam is able to detect ammonia and nitrogen dioxide at a concentration that is an order of magnitude lower than commercial gas detectors on the market today.”
The graphene foam can be engineered to detect many different gases beyond ammonia and nitrogen dioxide, he said.
Studies have shown the electrical conductivity of an individual nanotube, nanowire, or graphene sheet is acutely sensitive to gas adsorbtion. But the small size of individual nanostructures made it costly and challenging to develop into a device, plus the structures are delicate and often don’t yield consistent results.
The new graphene foam gas sensor overcomes these challenges. It is easy to handle and manipulate because of its large, macroscale size. The sensor also is flexible, rugged, and robust enough to handle wear and tear inside of a device. Plus it is fully reversible, and the results it provides are consistent and repeatable. Most important, the graphene foam is highly sensitive, thanks to its 3-D, porous structure that allows gases to easily adsorb to its huge surface area. Despite its large size, the graphene foam structure essentially functions as a single nanostructure. There are no breaks in the graphene network, which means there are no interfaces to overcome, and electrons flow freely with little resistance. This adds to the foam’s sensitivity to gases.
“In a sense we have overcome the Achilles’ heel of nanotechnology for chemical sensing,” Koratkar said. “A single nanostructure works great, but doesn’t mean much when applied in a real device in the real world. When you try to scale it up to macroscale proportions, the interfaces defeats what you’re trying to accomplish, as the nanostructure’s properties are dominated by interfaces. Now we’re able to scale up graphene in a way that the interfaces are not present. This allows us to take advantage of the intrinsic properties of the nanostructure, yet work with a macroscopic structure that gives us repeatability, reliability, and robustness, but shows similar sensitivity to gas adsorbtion as a single nanostructure.”
Along with Koratkar, co-authors of the paper are: Rensselaer graduate students Fazel Yavari and Abhay Varghese Thomas; along with professors W.C. Ren, H.M. Cheng and graduate student Z.P. Chen of the Shenyang National Laboratory for Materials Science at the Chinese Academy of Sciences.
Posted by: The Editors
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Artificial Photosynthesis Produces Renewable Hydrogen and Natural Gas
30 December 2011, 10:43
Categories: biomimicry energy
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U.S. solar tech company, HyperSolar Inc., states it has developed a process for creating natural gas from wastewater using solar power and has filed for a patent of the technology.
The company says they have designed a cheap and efficient nanoparticle system that can mimic a plant’s ability to photosynthesise light and separate hydrogen for water; essentially splitting the molecule – a process that usually requires considerable amounts of energy.
The extracted hydrogen is then mixed with carbon dioxide in a chemical process known as the Sabatier reaction to produce a renewable source of methane gas that HyperSolar envisions could be used as a replacement for traditional natural gas.
The company hopes to put the technology to work purifying industrial wastewater from factories municipal zones, while simultaneously creating renewable energy.
Each HyperSolar nanoparticle contains a tiny solar absorber in a protective shell. This provides energy for a photochemical reaction between a cathode and an anode specifically programmed to detoxify various wastewater streams, removing hydrogen and leaving behind clean water and usable chemical by-products.
The company’s vision is a global-scale supply of solar-engineered natural gas, with huge treatment plants containing hundreds of millions of solar nanoparticles pumping carbon-neutral methane to collection points for distribution to cities and homes.
HyperSolar CEO Tim Young says his company’s nanotechnology breakthrough will replace current destructive natural gas mining techniques, such as fracking.
“With global consumption projected to surpass coal in 2035, natural gas will be the next great fuel. From sunrise to sunset, our proprietary nanoparticles will work in a water based solution to produce clean and environmentally friendly renewable natural gas that can be collected for later use in power plants, industrial plants and vehicles – anywhere and anytime.”
Posted by: The Editors
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NIST Releases First Certified Reference Material For Single-Wall Carbon Nanotubes
30 December 2011, 10:18
Categories: nanotubes-wires-fullerenes other
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The National Institute of Standards and Technology (NIST) has issued the world’s first reference material for single-wall carbon nanotube soot. Distantly related to the soot in your fireplace or in a candle flame, nanotube-laden soot is the primary industrial source of single-wall carbon nanotubes, perhaps the archetype of all nanoscale materials. The new NIST material offers companies and researchers a badly needed source of uniform and well-characterized carbon nanotube soot for material comparisons, as well as chemical and toxicity analysis.
With walls of carbon only one atom thick and looking like a sheet of chicken wire curled into a cylinder, single-wall carbon nanotubes are one of several families of pure carbon materials that, because of their nanoscale size, have special properties. “Single-wall carbon nanotubes,” says NIST chemical engineer Jeffery Fagan, “have exquisite optical, mechanical, thermal and electronic properties, and because of their small width but long lengths—think of something like a long piece of hair but 10,000 times thinner—full development of these materials should enable lighter, stronger materials, as well as improve many technologies from sensors to electronics and batteries.”
Unfortunately, nanotubes are difficult to produce without significant impurities or in large quantities. Single-wall nanotubes, in particular, have been notorious for their relatively low quality and batch-to-batch variability. They typically are produced in complex processes using small particles of metal catalysts that promote the growth of the nanotubes. The resulting material—often a powder not unlike the soot you would find in your fireplace—has frequently contained large amounts of impurities, such as other forms of carbon, and sometimes significant levels of catalysts.
“One of the issues that this reference material addresses is that there’s no homogeneous lot that people can buy to do comparative measurements,” says Fagan. “Even batch-to-batch, raw carbon nanotube powder samples have varied so much that there is no interlaboratory consistency. And that’s particularly a problem for comparisons such as toxicity measurements. If you bought carbon nanotubes, you were pretty much guaranteed that your sample could be so different from anyone else’s samples that either your measurements could be specific to some flaw of your material, or that others might not be able to reproduce what you were doing.”
To address these issues, a multidisciplinary research team at NIST has worked to develop the metrology necessary for quantitative single-wall carbon nanotube measurements through a three-prong approach: basic measurement and separation science, documentary protocols and standards through international standards organizations, and now certified reference materials.
The new $865.00 NIST product, Standard Reference Material (SRM) 2483, Single-Wall Carbon Nanotubes (Raw Soot), will directly address the issue of comparability. It is possibly the world’s single largest supply of homogeneous, chemically analyzed, carbon nanotube soot where the uniformity of the samples from unit to unit is assured. Each unit of SRM 2483, a glass vial containing 250 milligrams of soot, is certified by NIST for the mass fraction values of several common contaminants: barium, cerium, chlorine, cobalt, dysprosium, europium, gadolinium, lanthanum, molybdenum and samarium. Reference values (values believed to be accurate, but not rising to the level of confidence that NIST certifies) are provided for an additional seven elements.
NIST also provides additional reference data useful for nanotube analysis, including thermal gravimetric and Raman data, as well as informational values for ultraviolet-visible-near-infrared absorbance spectra, near-infrared fluorescence spectra, Raman scattering spectra and scanning electron microscopy images. With these sets of information, purchasers of the material should be able to compare their results against the NIST values and against those from suppliers or after processing, ensuring a consistent point of comparison.
Posted by: The Editors
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