Posts Tagged ‘carbon nanotubes’
Monday, January 20, 2014 @ 03:01 PM gHale
In a solid safety move at the nanoscale, it is possible to create a uniform, multi-walled carbon-nanotube-based coating that greatly reduces the flammability of foam commonly used in upholstered furniture and other soft furnishings.
The flammability of the nanotube-coated polyurethane foam went down 35 percent compared with untreated foam. Just as important, the coating prevented melting and pooling of the foam, which generates additional flames that are a major contributor to the spread of fires.
Nationwide, fires in which upholstered furniture is the first item ignited account for about 6,700 home fires annually and result in 480 deaths, or almost 20 percent of home fire deaths between 2006 and 2010, according to the National Fire Protection Association.
The technique, created by researchers at National Institute of Standards and Technology (NIST), squeezes nanotubes between two everyday polymers and stacks four of these trilayers on top of each other. The result is a plastic-like coating that is thinner than one-hundredth the diameter of human hair and has flame-inhibiting nanotubes distributed evenly throughout.
The brainchild of NIST materials scientists Yeon Seok Kim and Rick Davis, the duo said the technique can work with a variety of types of nanoparticles to improve the quality of surface coatings for diverse applications.
The pair experimented with a variety of layer-by-layer coating methods before arriving at their triple-decker approach. All had failed to meet their three key objectives: Entire coverage of the foam’s porous surface, uniform distribution of the nanotubes, and the practicality of the method. In most of these trials, the nanotubes — cylinders of carbon atoms resembling rolls of chicken wire — did not adhere strongly to the foam surface.
Kim and Davis opted to doctor the nanotubes themselves, borrowing a technique often used in cell culture to make DNA molecules stickier. The method attached nitrogen-containing molecules — called amine groups — to the nanotube exteriors.
This step proved critical: The doctored nanotubes ended up uniformly distributed and clung tenaciously to the polymer layers above and below. As a result, the coating fully exploits the nanotubes’ rapid heat-dissipating capability.
Gram for gram, the resulting coating confers much greater resistance to ignition and burning than achieved with the brominated flame retardants commonly used to treat soft furnishings today. As important, a “protective char layer” forms when the nanotube-coated foam suffers exposure to extreme heat, creating a barrier that prevents the formation of melt pools, Davis said.
“This kind of technology has the potential to reduce the fire threat associated with burning soft furniture in homes by about a third,” Davis said.
Wednesday, October 16, 2013 @ 12:10 PM gHale
Graphene is capable of blocking almost everything and companies are already taking advantage of the capabilities by adapting these characteristics to applications like filtration and desalinization. But there is much more to come.
Graphene’s impermeability also makes it a fit for cars that run on natural gas, said researchers at Rice University.
Right now, natural gas packs away into heavy metal tanks that end up stored somewhere on a car. The researchers were able to combine plastic and graphene to create a plastic tank capable of holding natural gas. These lighter plastic tanks could make cars more efficient by lowering the amount of fuel they need.
“The idea is to increase the toughness of the tank and make it impermeable to gas,” said Rice chemist James Tour. “This becomes increasingly important as automakers think about powering cars with natural gas. Metal tanks that can handle natural gas under pressure are often much heavier than the automakers would like.”
Because it is not yet affordable to manufacture sheets of graphene in bulk, the researchers turned to graphene nanoribbons. Nanoribbons end up manufactured by unzipping carbon nanotubes. Those nanotubes are really rolled up pieces of graphene. Carbon nanotube manufacturing ends up being more advanced than graphene manufacturing, as is graphene nanoribbon manufacturing.
Researchers then embed the nanoribbons in the plastic. While this combination is more permeable than a solid sheet of graphene, it is still 1,000 times harder for gas to escape than if the researchers used a plain plastic wall.
The researchers said their creation also can work for soda and beer bottles. Adding graphene to plastic bottles would extend the shelf life of soda before it goes flat. And, plastic bottles laced with graphene could keep beer fresh. Brewers do not use plastic bottles or beer now because oxygen can enter them, causing the suds to go bad.
Wednesday, March 21, 2012 @ 12:03 PM gHale
A robotic jellyfish, oddly named Robojelly, not only works for underwater search and rescue operations, but could also never run out of energy because it uses hydrogen fuel.
Constructed from a set of smart materials, which have the ability to change shape or size as a result of a stimulus, and carbon nanotubes, Robojelly mimics the natural movements of a jellyfish when placed in a water tank and gets power by chemical reactions taking place on its surface.
“To our knowledge, this is the first successful powering of an underwater robot using external hydrogen as a fuel source,” said Virginia Tech’s Yonas Tadesse, lead author of a study on the subject.
The jellyfish is an ideal invertebrate to base the vehicle on because of its simple swimming action: It has two prominent mechanisms known as “rowing” and “jetting”.
A jellyfish’s movement is down to circular muscles located on the inside of the bell – the main part of the body shaped like the top of an umbrella. As the muscles contract, the bell closes in on itself and ejects water to propel the jellyfish forward. After contracting, the bell relaxes and regains its original shape.
They were able to replicate the movement in the vehicle using commercially-available shape memory alloys (SMA) – smart materials that “remember” their original shape – wrapped in carbon nanotubes and coated with a platinum black powder.
The robot gets its power by heat-producing chemical reactions between the oxygen and hydrogen in water and the platinum on its surface. The heat given off by these reactions transfers to the artificial muscles of the robot, causing them to transform into different shapes.
This green, renewable element means Robojelly can regenerate fuel from its natural surroundings and therefore doesn’t require an external power source or the constant replacement of batteries.
At the moment, the hydrogen-powered Robojelly has been functioning while clamped down in a water tank. Researchers said the robot still needs development to achieve full functionality and efficiency.
“The current design allows the jellyfish to flex its eight bell segments, each operated by a fuel-powered SMA module. This should be sufficient for the jellyfish to lift itself up if all the bell segments are actuated.
“We are now researching new ways to deliver the fuel into each segment so that each one can be controlled individually. This should allow the robot to be controlled and moved in different directions,” Tadesse said.
Tuesday, January 31, 2012 @ 02:01 PM gHale
Paint may end up being the biggest safety enhancer for critical infrastructure.
That is because a low-cost smart paint can detect microscopic faults in wind turbines, mines and bridges before structural damage occurs. The environmentally-friendly paint uses nanotechnology to detect movement in large structures, and could shape the future of safety monitoring.
Traditional methods of assessing large structures are complex, time consuming and use expensive instrumentation, with costs spiraling into millions each year.
However, the smart paint costs just a fraction of the cost and can spray onto any surface, with electrodes attached to detect structural damage long before failure occurs, said researchers at the University of Strathclyde in Glasgow, Scotland.
“The development of this smart paint technology could have far-reaching implications for the way we monitor the safety of large structures all over the world,” said Dr Mohamed Saafi, of the University’s Department of Civil Engineering. “There are no limitations as to where it could be used and the low-cost nature gives it a significant advantage over the current options available in the industry. The process of producing and applying the paint also gives it an advantage as no expertise is required and monitoring itself is straightforward.”
The paint uses a recycled waste product known as fly ash and highly aligned carbon nanotubes. When mixed it has a cement-like property which makes it useful in harsh environments.
“The process of monitoring involves in effect a wireless sensor network,” Saafi said. “The paint is interfaced with wireless communication nodes with power harvesting and warning capability to remotely detect any unseen damage such as micro-cracks in a wind turbine concrete foundation.
“Wind turbine foundations are currently being monitored through visual inspections. The developed paint with the wireless monitoring system would significantly reduce the maintenance costs and improve the safety of these large structures.
“Current technology is restricted to looking at specific areas of a structure at any given time, however, smart paint covers the whole structure which is particularly useful to maximize the opportunity of preventing significant damage.”
With fly ash the main material used to make the paint, it costs just one percent of the alternative widely used inspection methods.
Prototype tests show the paint is highly effective. More tests will occur in Glasgow.
“We are able to carry out the end-to-end process at the University and we are hoping that we can now demonstrate its effectiveness on a large structure,” Saafi said.
“The properties of the fly ash give the paint a durability that will allow it to be used in any environment which will be a massive advantage in areas where the weather can make safety monitoring particularly difficult.
“The smart paint represents a significant development and is one that has possibly been overlooked as a viable solution because research tends to focus on high-tech options that look to eliminate human control. Our research shows that by maintaining the human element the costs can be vastly reduced without an impact on effectiveness.”
Monday, October 31, 2011 @ 04:10 PM gHale
A new prototype wireless sensor is capable of detecting trace amounts of a key ingredient found in quite a few explosives.
The device, which employs carbon nanotubes and prints on paper or paper-like material using standard inkjet technology, could be deploy in large numbers to alert authorities to the presence of explosives, such as improvised explosive devices (IEDs).
“This prototype represents a significant step toward producing an integrated wireless system for explosives detection,” said Krishna Naishadham, a principal research scientist who is leading the work at the Georgia Tech Research Institute (GTRI). “It incorporates a sensor and a communications device in a small, low-cost package that could operate almost anywhere.”
Other types of hazardous gas sensors rely upon expensive semiconductor fabrication and gas chromatography, Naishadham said, and they consume more power, require human intervention, and typically do not operate at ambient temperatures. Furthermore, those sensors do not have communication devices such as antennas.
The wireless component for communicating the sensor information — a resonant lightweight antenna – printed on photographic paper using inkjet techniques devised by Professor Manos Tentzeris of Georgia Tech’s School of Electrical and Computer Engineering. Tentzeris is collaborating with Naishadham on development of the sensing device.
Xiaojuan (Judy) Song, a GTRI research scientist, fabricated and tested the sensing component, based on functionalized carbon nanotubes (CNTs). The device relies on carbon-nanotube materials optimized by Song.
This is not the first inkjet-printed ammonia sensor integrated with an antenna on paper, Tentzeris said. His group produced a similar integrated sensor last year in collaboration with the research group of C.P. Wong, who is Regents professor and Smithgall Institute Endowed Chair in the School of Materials Science and Engineering at Georgia Tech.
“The fundamental difference is that this newest CNT sensor possesses dramatically improved sensitivity to miniscule ammonia concentrations,” Tentzeris said. “That should enable the first practical applications to detect trace amounts of hazardous gases in challenging operational environments using inkjet-printed devices.”
Tentzeris said the key to printing components, circuits and antennas lies in novel “inks” that contain silver nanoparticles in an emulsion that can “print out” from the printer at low temperatures – around 100 degrees Celsius. A process called sonication helps to achieve optimal ink viscosity and homogeneity, enabling uniform material deposition and permitting maximum operating effectiveness for paper-based components.
“Ink-jet printing is low-cost and convenient compared to other technologies such as wet etching,” Tentzeris said. “Using the proper inks, a printer can be used almost anywhere to produce custom circuits and components, replacing traditional clean-room approaches.”
Low-cost materials – such as heavy photographic paper or plastics like polyethylene terephthalate — can be water resistant to ensure greater reliability, he added. Inkjet component printing can also use flexible organic materials, such as liquid crystal polymers (LCP), known for their robustness and weather resistance. The resulting components are similar in size to conventional components but can conform and adhere to almost any surface.
Naishadham explained the same inkjet techniques used to produce RF components, circuits and antennas can also deposit the functionalized carbon nanotubes used for sensing. These nanoscale cylindrical structures — about one-billionth of a meter in diameter, or 1/50,000th the width of a human hair – come alive after coating them with a conductive polymer that attracts ammonia, a major ingredient found in IEDs.
Sonication of the functionalized carbon nanotubes produces a uniform water-based ink that can print side-by-side with RF components and antennas to produce a compact wireless sensor node.
“The optimized carbon nanotubes are applied as a sensing film, with specific functionalization designed for a particular gas or analyte,” Song said. “The GTRI sensor detects trace amounts of ammonia usually found near explosive devices, and it can also be designed to detect similar gases in household, healthcare and industrial environments at very low concentration levels.”
The sensor has been designed to detect ammonia in trace amounts – as low as five parts per million, Naishadham said.
The resulting integrated sensing package can potentially detect the presence of trace explosive materials at a distance, without endangering human lives. This approach, called standoff detection, involves the use of RF technology to identify explosive materials at a relatively safe distance. The GTRI team has designed the device to send an alert to nearby personnel when it detects ammonia.
The wireless sensor nodes require relatively low power, which could come from a number of technologies including thin-film batteries, solar cells or power-scavenging and energy-harvesting techniques. In collaboration with Tentzeris’s and Wong’s groups, GTRI is investigating ways to make the sensor operate passively, without any power consumption.
“We are focusing on providing standoff detection for those engaged in military or humanitarian missions and other hazardous situations,” Naishadham said. “We believe that it will be possible, and cost-effective, to deploy large numbers of these detectors on vehicles or robots throughout a military engagement zone.”
Wednesday, August 31, 2011 @ 12:08 PM gHale
Wind energy continues to grow, but the efforts to build larger turbines able to capture more power from the air remain stilted because of the weight of blades. But that may soon change.
A prototype blade substantially lighter and eight times tougher and more durable than current blade materials is now in development, said Marcio Loos, a post-doctoral researcher in the Case Western Reserve University Department of Macromolecular Science and Engineering. He is comparing the properties of new materials with the current standards used in blade manufacturing with a team from Case Western, Bayer MaterialScience in Pittsburgh, and Molded Fiber Glass Co. in Ashtabula, Ohio.
Loos started this idea when he would go into the lab on weekends and he built a polyurethane blade reinforced with carbon nanotubes. He wanted to be sure the composite that was scoring best on preliminary tests could mold into the right shape and at the same time maintain its strength properties.
Using a small commercial blade as a template, he made a 29-inch blade that is substantially lighter, more rigid and tougher.
“The idea behind all this is the need to develop stronger and lighter materials which will enable manufacturing of blades for larger rotors,” Loos said.
In order to achieve the expansion expected in the market for wind energy, turbines need a bigger share of the wind. But, simply building larger blades isn’t a smart answer.
The heavier the blades, they need more wind to turn the rotor. That means capturing less energy. And the more the blades flex in the wind, the more they lose the optimal shape for catching moving air, so they capture even less energy.
Lighter, stiffer blades enable maximum energy and production.
“Results of mechanical testing for the carbon nanotube reinforced polyurethane show that this material outperforms the currently used resins for wind blades applications,” said Ica Manas-Zloczower, professor of macromolecular science and engineering and associate dean in the Case School of Engineering.
Loos is working in the Manas-Zloczower lab where she and Chemical Engineering Professor Donald L. Feke, a vice provost at the university, serve as advisors on the project.
In a comparison of reinforcing materials, the researchers found carbon nanotubes are lighter per unit of volume than carbon fiber and aluminum and had more than 5 times the tensile strength of carbon fiber and more than 60 times that of aluminum.
Fatigue testing showed the reinforced polyurethane composite lasts about eight times longer than epoxy reinforced with fiberglass. The new material was also about eight times tougher in delamination fracture tests.
The performance in each test was even better when compared to vinyl ester reinforced with fiberglass, another material used to make blades.
The new composite also has shown fracture growth rates at a fraction of the rates found for traditional epoxy and vinyl ester composites.
Loos and the rest of the team are continuing to test for the optimal conditions for the stable dispersion of nanotubes, the best distribution within the polyurethane and methods to make that happen.
The functional prototype blades built by Loos, which turned a 400-watt turbine, will remain stored in the laboratory, Manas-Zloczower said. “They will be used to emphasize the significant potential of carbon nanotube reinforced polyurethane systems for use in the next generation of wind turbine blades.”
Wednesday, September 15, 2010 @ 09:09 PM gHale
There is now a way to concentrate solar energy 100 times more than a regular photovoltaic cell by using carbon nanotubes.
These nanotubes could form antennas that capture and focus light energy, potentially allowing much smaller and more powerful solar arrays.
“Instead of having your whole roof be a photovoltaic cell, you could have little spots that were tiny photovoltaic cells, with antennas that would drive photons into them,” said Michael Strano, the MIT Charles and Hilda Roddey Associate Professor of Chemical Engineering and leader of the research team.
Their new antennas, or “solar funnels,” might also be useful for other applications that require concentrated light, such as night-vision goggles or telescopes.
Solar panels generate electricity by converting photons (packets of light energy) into an electric current. Strano’s nanotube antenna boosts the number of photons they can capture and transform the light into energy they can funnel into a solar cell.
The antenna consists of a fibrous rope about 10 micrometers (millionths of a meter) long and four micrometers thick, containing about 30 million carbon nanotubes. Strano’s team built, for the first time, a fiber made of two layers of nanotubes with different electrical properties — specifically, different bandgaps.
In any material, electrons can exist at different energy levels. When a photon strikes the surface, it excites an electron to a higher energy level, which is specific to the material. The interaction between the energized electron and the hole it leaves behind is an exciton, and the difference in energy levels between the hole and the electron is the bandgap.
The inner layer of the antenna contains nanotubes with a small bandgap, and nanotubes in the outer layer have a higher bandgap. That’s important because excitons like to flow from high to low energy. In this case, that means the excitons in the outer layer flow to the inner layer, where they can exist in a lower (but still excited) energy state.
Therefore, when light energy strikes the material, all of the excitons flow to the center of the fiber, where they are concentrated. Strano and his team have not yet built a photovoltaic device using the antenna, but they plan to. In such a device, the antenna would concentrate photons before the photovoltaic cell converts them to an electrical current. This could happen by constructing the antenna around a core of semiconducting material.
The interface between the semiconductor and the nanotubes would separate the electron from the hole, with electrons collected at one electrode touching the inner semiconductor, and holes collected at an electrode touching the nanotubes. This system would then generate electric current. The efficiency of such a solar cell would depend on the materials used for the electrode, the researchers said.
Strano’s team is the first to construct nanotube fibers in which they can control the properties of different layers, an achievement made possible by advances in separating nanotubes with different properties.
While the cost of carbon nanotubes was once prohibitive, it has been coming down in recent years as chemical companies build up their manufacturing capacity. “At some point in the near future, carbon nanotubes will likely be sold for pennies per pound, as polymers are sold,” Strano said. “With this cost, the addition to a solar cell might be negligible compared to the fabrication and raw material cost of the cell itself, just as coatings and polymer components are small parts of the cost of a photovoltaic cell.”
Strano’s team is now working on ways to minimize the energy lost as excitons flow through the fiber, and on ways to generate more than one exciton per photon. The nanotube bundles lose about 13 percent of the energy they absorb, but the team is working on new antennas that would lose only 1 percent.
Wednesday, September 15, 2010 @ 08:09 PM gHale
Sometimes something, like single ions marching through a tiny carbon-nanotube channel, can end up being something very big.
These tiny channels could end up being extremely sensitive detectors or part of a new water-desalination system. They could also allow scientists to study chemical reactions at the single-molecule level.
Carbon nanotubes — tiny, hollow cylinders whose walls are lattices of carbon atoms — are 10,000 times thinner than a human hair. Since their discovery nearly 20 years ago, researchers have experimented with them as batteries, transistors, sensors and solar cells, among other applications.
But now they are finding charged molecules, such as the sodium and chloride ions that form when salt dissolves in water, can not only flow rapidly through carbon nanotubes, but also can, under some conditions, do so one at a time, like people taking turns crossing a bridge, said MIT Associate Professor Michael Strano.
The new system allows passage of much smaller molecules, over greater distances (up to half a millimeter), than any existing nanochannel. Currently, the most commonly studied nanochannel is a silicon nanopore, made by drilling a hole through a silicon membrane. However, these channels are much shorter than the new nanotube channels (the nanotubes are about 20,000 times longer), so they only permit passage of large molecules such as DNA or polymers — anything smaller would move too quickly for detection.
Strano and his team built their new nanochannel by growing a nanotube across a one-centimeter-by-one-centimeter plate, connecting two water reservoirs. Each reservoir contained an electrode, one positive and one negative. Because electricity can flow only if protons — positively charged hydrogen ions, which make up the electric current — can travel from one electrode to the other, the researchers can easily determine whether ions are traveling through the nanotube.
They found protons do flow steadily across the nanotube, carrying an electric current. Protons flow easily through the nanochannel because they are so small, but the researchers observed other positively charged ions, such as sodium, can also get through but only if they apply enough electric field. Sodium ions are much larger than protons, so they take longer to cross once they enter. While they travel across the channel, they block protons from flowing, leading to a brief disruption in current known as the Coulter effect.
Strano said the channels allow only positively charged ions to flow through them because the ends of the tubes contain negative charges, which attract positive ions. However, he plans to build channels that attract negative ions by adding positive charges to the tube.
Once the researchers have these two types of channels, they hope to embed them in a membrane they could use for water desalination. More than 97 percent of Earth’s water is in the oceans, but that vast reservoir is undrinkable unless they are able to remove the salt. Current desalination methods, distillation and reverse osmosis, are expensive and require lots of energy. So a nanotube membrane that allows sodium and chloride ions to flow out of seawater could become a cheaper way to desalinate water.
Strano’s research marks the first time they were able to observe individual ions dissolved in water at room temperature. This means the nanochannels could also detect impurities, such as arsenic or mercury, in drinking water.
“If a single arsenic ion is floating in solution, you could detect it,” Strano said.