NASA engineers develop 'blacker than black' nanotubes (w/ Video)

Enlarge

Principal Investigator John Hagopian developed a new nanotech-based material that is 10 times more effective than black paint used by instrument developers to absorb stray light, which can contaminate scientific data. The sample on the left is black paint typically used to suppress errant light in instruments; the sample on the right is the new nanotube material. Credit: Chris Gunn/NASA

The nanotech-based material now being developed by a team of 10 technologists at the NASA Goddard Space Flight Center in Greenbelt, Md., is a thin coating of multi-walled carbon nanotubes — tiny hollow tubes made of pure carbon about 10,000 times thinner than a strand of human hair. Nanotubes have a multitude of potential uses, particularly in electronics and advanced materials due to their unique electrical properties and extraordinary strength. But in this application, NASA is interested in using the technology to help suppress errant light that has a funny way of ricocheting off instrument components and contaminating measurements.

Better than Paint

"This is a technology that offers a lot of payback," said engineer Leroy Sparr, who is assessing its effectiveness on the Ocean Radiometer for Carbon Assessment (ORCA), a next-generation instrument that is designed to measure marine photosynthesis. "It's about 10 times better than black paint" typically used by NASA instrument designers to suppress stray light, he said.

Enlarge

Multi-walled carbon nanotubes are tiny hollow tubes made of pure carbon about 10,000 times thinner than a strand of human hair. NASA is investigating their use to help suppress errant light that ricochets off instrument components and contaminates measurements. Credit: NASA

The technology works because of its super-absorption abilities. The nanotubes themselves are packed vertically much like a shag rug. The tiny gaps between the tubes absorb 99.5 percent of the light that hits them. In other words, very few photons are reflected off the carbon-nanotube coating, which means that stray light cannot reflect off surfaces and interfere with the light that scientists actually want to measure. The human eye sees the material as black because only a small fraction of light reflects off the material.

The team began working on the technology in 2007. Unbeknownst to the group, the New York-based Rensselaer Polytechnic Institute also had initiated a similar effort and announced in 2008 that its researchers had developed the darkest carbon nanotube-based material ever made — more than three times darker than the previous record.

"Our material isn't quite as dark as theirs," said John Hagopian, the principal investigator leading the development team. "But what we're developing is 10 times blacker than current NASA paints that suppress system stray light. Furthermore, it will be robust for space applications," he said.

You need Flash installed to watch this video

NASA's Goddard Space Flight Center has a team of scientists testing micro and nanotechnology to use on spacecraft. The goal is to reduce the reflection off the surface of instruments satellites so that the data does not get polluted by the scattered light. The carbon nanotubes that the team grows have proven to be 10 times better than the NASA Z306 paint, currently used on spacecraft instruments.

That is an important distinction, said Carl Stahle, assistant chief of technology for Goddard's Instrument Systems and Technology Division. Not all technology can be used in space because of the harsh environmental conditions encountered there. "That's the real strength of this effort," Stahle said. "The group is finding ways to apply new technology and fly it on our instruments."

Big Breakthrough

The breakthrough was the discovery of a highly adhesive underlayer material upon which to grow the carbon nanotubes, which are just a few tens of nanometers in diameter. To grow carbon nanotubes, materials scientists typically apply a catalyst layer of iron to an underlayer on the silicon substrate. They then heat the material in an oven to about 750° C (1,382° F). While heating, the material is bathed in carbon-containing feedstock gas.

Stephanie Getty, the materials scientist on Hagopian's team, varied the underlayer as well as the thickness of the catalyst materials to create carbon nanotubes that not only absorb light, but also remain fixed to the material upon which they are grown. As a result, they are more durable and less likely to scratch off. The team also has grown durable nanotube coatings on titanium, a better structural material for space use. The team now is fine-tuning production techniques to assure consistent quality and light-suppression capabilities, Hagopian said.

New Capabilities Added

Should the team prove the material's suitability in space, the material would provide real benefits to instrument developers, Hagopian added.

Currently, instrument developers apply black paint to baffles and other components to reduce stray light. Because reflectance tests have shown the coating to be more effective than paint, instrument developers could grow the carbon nanotubes on the components themselves, thereby simplifying instrument designs because fewer baffles would be required. To accommodate larger components, the team now is installing a six-inch furnace to grow nanotubes on components measuring up to five inches in diameter. And under a NASA R&D award, the team also is developing a separate technique to create sheets of nanotubes that could be applied to larger, non-conforming surfaces.

In addition to simplifying instrument design, the technology would allow scientists to gather hard-to-obtain measurements because of limitations in existing light-suppression techniques or to gather information about objects in high-contrast areas, including planets in orbit around other stars, Hagopian said.

The ORCA team, which is fabricating and aligning an instrument prototype, is the first to actually apply and test the technology. The instrument is the front-runner for the proposed Aerosol/Cloud/Ecosystems (ACE) mission and requires robust light-suppression technologies because more than 90 percent of the light gathered by the instrument comes from the atmosphere. Therefore, the team is looking for a technique to suppress the light so that it doesn't contaminate the faint signal the team needs to retrieve.

"It's been an issue with all the (ocean sensors) we've flown so far," said ORCA Principal Investigator Chuck McClain.

Working with the ORCA team, Hagopian's group grew the coating on a slit, the conduit through which all light will pass on ORCA. "Having an efficient absorber is critical and the nanotubes could provide the solution," McClain said. "Right now, it looks promising," Sparr added. "If I can support them and they can continue advancing the technology so that it can be applied to other spacecraft components, it could be a very important development for NASA."

Goddard Chief Technologist Peter Hughes agrees, and, in fact, selected Hagopian and his team to receive his organization’s 2010 "Innovator of the Year" award. "Our job is to develop and advance new technology that will ultimately result in better scientific measurements. Goddard has a well-deserved reputation for creating technologies that enhance instrument performance because we are adept at quickly infusing emerging technology for specific spaceflight applications. John’s team demonstrated that key strength. And in doing so, he’s leading the way in NASA’s quest to bring about a new level of scientific discovery," Hughes said.

Light touch brightens nanotubes (w/ Video)

Single-walled carbon nanotubes treated with ozone incorporate oxygen atoms that shift and intensify the nanotubes' near-infrared fluorescence emission. The discovery by Rice University scientists should lead to new uses of nanotubes in biomedicine and materials science. (Credit: Bruce Weisman/Rice University)

The Rice lab of researcher Bruce Weisman, a pioneer in nanotube spectroscopy, found that adding tiny amounts of ozone to batches of single-walled carbon nanotubes and exposing them to light decorates all the nanotubes with oxygen atoms and systematically changes their near-infrared fluorescence.

Chemical reactions on nanotube surfaces generally kill their limited natural fluorescence, Weisman said. But the new process actually enhances the intensity and shifts the wavelength.

He expects the breakthrough, reported online in the journal Science, to expand opportunities for biological and material uses of nanotubes, from the ability to track them in single cells to novel lasers.

Best of all, the process of making these bright nanotubes is incredibly easy -- "simple enough for a physical chemist to do," said Weisman, a physical chemist himself.

He and primary author Saunab Ghosh, a graduate student in his lab, discovered that a light touch was key. "We're not the first people to study the effects of ozone reacting with nanotubes," Weisman said. "That's been done for a number of years.

"But all the prior researchers used a heavy hand, with a lot of ozone exposure. When you do that, you destroy the favorable optical characteristics of the nanotube. It basically turns off the fluorescence. In our work we only add about one oxygen atom for 2,000-3,000 carbon atoms, a very tiny fraction."

You need Flash installed to watch this video

Ghosh and Weisman started with a suspension of nanotubes in water and added small amounts of gaseous or dissolved ozone. Then they exposed the sample to light. Even light from a plain desk lamp would do, they reported.

Most sections of the doped nanotubes remain pristine and absorb infrared light normally, forming excitons, quasiparticles that tend to hop back and forth along the tube -- until they encounter oxygen.

"An exciton can explore tens of thousands of carbon atoms during its lifetime," Weisman said. "The idea is that it can hop around enough to find one of these doping sites, and when it does, it tends to stay there, because it's energetically stable. It becomes trapped and emits light at a longer (red-shifted) wavelength.

"Essentially, most of the nanotube is turning into an antenna that absorbs light energy and funnels it to the doping site. We can make nanotubes in which 80 to 90 percent of the emission comes from doped sites," he said.

Lab tests found the doped nanotubes' fluorescent properties to be stable for months.

Weisman said treated nanotubes could be detected without using visible light. "Why does that matter? In biological detection, any time you excite at visible wavelengths, there's a little bit of background emission from the cells and from the tissues. By exciting instead in the infrared, we get rid of that problem," he said.

The researchers tested their ability to view doped nanotubes in a biological environment by adding them to cultures of human uterine adenocarcinoma cells. Later, images of the cells excited in the near-infrared showed single nanotubes shining brightly, whereas the same sample excited with visible light displayed a background haze that made the tubes much more difficult to spot.

His lab is refining the process of doping nanotubes, and Weisman has no doubt about their research potential. "There are many interesting scientific avenues to pursue," he said. "And if you want to see a single tube inside a cell, this is the best way to do it. The doped tubes can also be used for biodistribution studies.

"The nice thing is, this isn't an expensive or elaborate process," Weisman said. "Some reactions require days of work in the lab and transform only a small fraction of your starting material. But with this process, you can convert an entire nanotube sample very quickly."

A greener way to grow carbon nanotubes

Enlarge

Graphic: Christine Daniloff

Given their size, strength and electrical properties, carbon nanotubes — tiny, hollow cylinders made of carbon atoms — hold promise for a range of applications in electronics, medicine and other fields. Despite industrial development of nanotubes in recent years, however, very little is known about how they form or the environmental impacts of their manufacture.

It turns out that one process commonly used to produce carbon nanotubes, or CNTs, may release several hundred tons of chemicals, including greenhouse gases and hazardous air pollutants, into the air each year. In a paper published last week on the ACS Nano website, the researchers report that in experiments, removing one step in that process — a step that involves heating carbon-based gases and adding key reactive “ingredients” — reduced emissions of harmful by-products at least tenfold and, in some cases, by a factor of 100. It also cut the amount of energy used in the process by half.

“We were able to do all of this and still have good CNT growth,” says Desiree Plata, who led the research between 2007 and 2009 as a doctoral student in MIT’s joint program with the Woods Hole Oceanographic Institution. Now a visiting assistant professor in MIT’s Departments of Aeronautics and Astronautics and Civil and Environmental Engineering (CEE), Plata collaborated on the paper with several MIT and University of Michigan researchers, including Philip Gschwend, Ford Professor of Engineering in CEE, and John Hart, a mechanical engineering professor at the University of Michigan. The study is part of a long-term effort to change the approach to material development so that environmental chemists work with the young CNT industry to develop methods to prevent or limit undesirable environmental consequences.

In their study, Plata and her colleagues analyzed a common CNT manufacturing process known as catalytic chemical vapor deposition. In this method, manufacturers combine hydrogen with a “feedstock gas,” such as methane, carbon monoxide or ethylene. They then heat the combination in a reactor that contains a metal catalyst like nickel or iron, which then forms CNTs. The problem is that once the CNTs form, unreacted compounds (up to 97 percent of the initial feedstock) are often released into the air.

Turning off the heat

In a custom-made laboratory-scale reactor, the researchers heated hydrogen and ethylene, which is commonly used in high-volume CNT manufacturing, and then delivered it to a metal catalyst. They found that more than 40 compounds formed, including greenhouse gases like methane and toxic air pollutants like benzene.

The researchers suspected that not all of those compounds were essential for growing CNTs, and they knew that heating the feedstock gas plays a critical role in creating the dangerous compounds. So they combined unheated ethylene and hydrogen with several of the 40 compounds, one by one, to see which combination of compounds led to the best growth. They observed that certain alkynes, or molecules that have at least two carbon atoms stuck together with three distinct bonds, produced the best growth, while other compounds that are undesirable by-products, such as methane and benzene, did not.

Plata and her colleagues accomplished their dramatic reduction in both harmful emissions and energy consumption by impinging room-temperature alkynes, with ethylene and hydrogen, directly onto the metal catalyst, without heat. They also learned that they could reduce the amount of ethylene and hydrogen used by about 20 and 40 percent, respectively, and still achieve the same rate and quality of CNT growth. Plata says that while the results of lab experiments are hard to generalize, in a market that is expected to reach several billion dollars within several years, these changes could translate into “significant cost savings” for manufacturers.

Industry reaction

Although it’s too soon for manufacturers to adopt the method presented in the paper, David Lashmore, vice president and chief technology officer of Concord, N.H.-based Nanocomp Technologies, says the method is something his company is willing to try as it looks for ways to minimize the environmental effects of its production process. “This is of high interest to us and could have a broad impact on our process economics,” he says.

Plata points out that the MIT study analyzed only one of several feedstock gases used to make CNTs, and that the same analysis needs to be done for the others. But for her own part, she is now focusing on how CNTs form, trying to determine the precise interaction of the metal catalyst and the hydrocarbons in this process. Knowing the catalyst’s role could help researchers manipulate CNTs’ formation atom by atom — much more precisely than they can now, she says.
This story is republished courtesy of MIT News (http://web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

Provided by Massachusetts Institute of Technology (news : web)

'Express lanes' for ions: By aligning carbon nanotubes in electrodes, researchers boost performance

October 8, 2010 by Morgan Bettex

Enlarge

By aligning carbon nanotubes inside polymer composites, Wardle and his colleagues designed electrodes that allow ions to travel more quickly between the tiny cylinders. Image: Joe Klimek, Lazerpro Digital Media Group

Actuators are devices that convert electrical energy into mechanical energy, such as the battery-powered device inside a cell phone that causes the phone to vibrate. When this process is reversed -- when a device converts mechanical energy into electrical energy -- the device is called an energy harvester, and that electrical energy is often stored for future use. An example would be a device inside a pacemaker that converts mechanical energy created by the motion of a pair of breathing lungs into electrical energy that can be used to charge the pacemaker’s batteries.

Both devices typically contain electromechanical materials, such as electroactive polymers, that are made of chainlike molecules that change in size or shape when stimulated by an electric field. But their efficiency and speed depend on how quickly ions, or electrically charged particles, can move between electrodes, or the conductors that electric current passes through, to change the polymer’s size or shape. The faster ions can move between electrodes, the more ionic conductivity those electrodes will have and the more responsive the material will be to the electric field. Although these polymers usually contain nanoparticles that are randomly dispersed throughout the material to make it conductive, this slows ions by forcing them to travel in zigzag paths around the tiny particles.

Recently, an MIT researcher collaborated with a team of electrical engineers from Pennsylvania State University to devise a new way for ions to travel more quickly between electrodes than they do in traditional polymers. Brian L. Wardle, associate professor of aeronautics and astronautics, and his colleagues designed electrodes containing aligned carbon nanotubes — tiny, hollow cylinders made of carbon atoms — to be used in an electroactive polymer. As they report in a paper to be published Oct. 8 in Advanced Functional Materials, this alignment created “express lanes” that enabled the ions to travel more quickly between electrodes. Specifically, the researchers estimate that the ionic conductivity of these electrodes is about an order of magnitude greater than that of electrodes in polymers that contain randomly dispersed nanoparticles.

Wardle and his colleagues, including Qiming M. Zhang, a professor of electrical engineering at Penn State, and lead author Sheng Liu, one of Zhang’s graduate students, demonstrated that the aligned carbon-nanotube electrodes can enhance ion performance in an actuator, meaning they could be optimized for applications like artificial muscles and robots.

The researchers state that the devices could be used as energy harvesters through a reverse-conversion process. There is tremendous interest in developing energy harvesters for large-scale applications, such as to create electrical energy from the motion of wind or ocean waves, Wardle says. The devices could also be used to power vast networks of microscopic sensors in hard-to-reach areas like underground pipes.

Composite creation

The researchers’ goal was to design a composite that could function as a superior electrode. By heating natural gas and exposing it to a metal catalyst, Wardle and several of his graduate students grew the electrically conductive carbon nanotubes and poured a polymer mixed in a solvent over them. Once the solvent evaporated, it left behind a solid, ion-porous composite containing both polymer and carbon nanotubes. The researchers then used this composite to create a structure comprised of one layer of pure polymer (to act as an insulator) containing both positive and negative ions sandwiched between two layers of the composite made of both polymer and carbon nanotubes (to act as electrodes).

To test the structure’s actuator abilities, the researchers applied a low-voltage electric field. This voltage caused ions to flow from one electrode layer to the other, which resulted in one side of the structure containing more ions. This ion imbalance generated enough pressure to cause the entire structure to bend, thereby creating mechanical energy. The experiment also revealed that the composite electrode design helped to minimize electrical resistance.

The researchers believe the same device could be used as an energy harvester if it is stressed mechanically, such as through compression. That’s because compression would make the ions move differently, which would cause an unbalanced electrical charge. This, in turn, would create a voltage difference and produce a flow of electricity.

Optimizing design

Yoseph Bar-Cohen, a senior research scientist at NASA’s Jet Propulsion Laboratory, says that the study demonstrates an improvement of ionic polymers. But he is curious about the response of the device over longer periods of time, noting that the current study was limited to only a 10-minute experiment.

As they develop these electrodes, Wardle and his collaborators are trying to determine an optimal design. Now that they have demonstrated how effective carbon nanotubes are for electrode efficiency, they are exploring certain details that might enable optimal performance, such as the spacing between the tiny tubes.
This story is republished courtesy of MIT News (http://web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

Carbon nanotubes twice as strong as once thought

Carbon nanotubes -- those tiny particles poised to revolutionize electronics, medicine, and other areas ? are much bigger in the strength department than anyone ever thought, scientists are reporting.

New studies on the strength of these submicroscopic cylinders of carbon indicate that on an ounce-for-ounce basis they are at least 117 times stronger than steel and 30 times stronger than Kevlar, the material used in bulletproof vests and other products. The findings, which could expand commercial and industrial applications of nanotube materials, appear in the monthly journal ACS Nano.

Stephen Cronin and colleagues point out that nanotubes ? barely 1/50,000th the width of a human hair ? have been renowned for exceptional strength, high electrical conductivity, and other properties. Nanotubes can stretch considerably like toffee before breaking. This makes them ideal for a variety of futuristic applications, even, if science fiction ever become reality, as cables in "space elevators" that lift objects from the Earth's surface into orbit.

To resolve uncertainties about the actual strength of nanotubes, the scientists applied immense tension to individual carbon nanotubes of different lengths and widths. They found that nanotubes could be stretched up to 14 percent of their normal length without breaking, or more than twice that of previous reports by others. The finding establishes "a new lower limit for the ultimate strength of carbon nanotubes," the article noted.

A versatile, clean and efficient way to enhance widespread application of carbon nanotubes

August 26, 2010 (PhysOrg.com) -- Researchers at Imperial College London have developed a versatile, practical and efficient method for activating sites on the surface of carbon nanotubes (CNTs) and subsequently binding a wide range of molecules to them. This new method will enable large-scale manufacture of modified CNTs.

The new method, reported this month in the journal Chemical Science, overcomes a major hurdle in the development of industrial scale applications for CNTs. It provides manufacturers with a method that, in principle, can be used to modify the surface chemistry of the underlying nanotube structure, on a large scale. Surface modification can provide new properties or enable subsequent processing steps: for example, molecules grafted to the CNTs may introduce catalytic activity or provide compatibility with particular solvents.

Our approach is potentially a very significant step towards manufacturing carbon nanotubes with specific chemical characteristics, so-called functionalisation, at an industrial scale," said Professor Milo Shaffer, lead author of the study from the Department Chemistry at Imperial College London. "Our method is extremely practical because, in principle, it can exploit existing infrastructure and yet it remains extremely versatile; the huge range of molecules that can be bound to the CNTs makes the technology adaptable to almost any application."

"Our technique is intrinsically scalable and, for the first time, it should be feasible to functionalise CNTs on the same scale as they are produced. This change is significant as industry's current capacity to manufacture CNTs is hundreds, if not thousands, of times greater than its capacity to add complex surface chemistry. This technique should increase the availability of functionalised CNTs, enable new applications that require manufacturing in bulk, and hence enhance the growth of the market," added Professor Shaffer.

The method that Professor Shaffer and his colleagues have developed should allow CNTs to be readily tailored to potential applications such as sensor networks, filters, electrodes for electrochemical devices, advanced catalysts and to improve CNT compatibility in, for example, composite materials, solvents, and electrolytes.

The key step in the new method involves activating CNTs at high temperatures under an inert atmosphere or vacuum. The high temperature treatment drives desorption of surface oxides on the CNT surface, producing reactive radicals that can subsequently bind a wide range of functional molecules to modify CNT physico-chemical properties. The radicals can also initiate the polymerisation of monomers, so that oligomers of functional molecules are bound to CNTs. The treatment does not cause any significant damage to the CNT structure, because the surface sites that it activates are already present on nanotubes manufactured using standard industrial methods. The number of reactive sites, and hence degree of functionalisation, can be increased by additional oxidation steps.

Professor Shaffer's team has demonstrated that the functional molecules are bound to, and uniformly distributed over, the surface of the CNTs. While the molecules are bound at relatively low densities, the degree of functionalisation is sufficient to offer benefits in industrial applications. The team has already demonstrated the attachment of catalytic metal particles, enhanced solubilities, and improved wetting with polymer matrices.

Professor Shaffer said: "The heat treatment to activate CNTs is compatible with some existing production technologies and can be easily adopted to work with others. Where the functional molecules to be added are volatile, the method can be carried out in the gas phase without the need for solvents, at any stage. The absence of solvent simplifies purification of the functionalised CNTs and, as many solvents used in wet-activation methods are corrosive and toxic, this option has environmental and hazard control benefits. It also has the advantage of being less damaging, less wasteful, and less time consuming than existing methods."

More information: A versatile, solvent-free methodology for the functionalisation of carbon nanotubes. Chemical Science 2010 DOI:10.1039/C0SC00287A

Provided by Imperial College London (news : web)

Rate this story - 5 /5 (6 votes)

Move the slider to adjust rank threshold, so that you can hide some of the comments.