Materials & Coatings

Fluoroester Co-Solvents for Low-Temperature Li+ Cells

Both low-temperature performance and high-temperature resilience are improved. Electrolytes comprising LiPF6 dissolved in alkyl carbonate/fluoroester mixtures have been found to afford improved low-temperature performance and greater high-temperature resilience in rechargeable lithium-ion electrochemical cells. These and other electrolytes comprising lithium salts dissolved mixtures of esters have been studied in continuing research directed toward extending the lower limit of operating temperatures of such cells. This research at earlier stages, and the underlying physical and chemical principles, were reported in numerous previous NASA Tech Briefs articles.

Posted in: Briefs, TSP

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Functionalizing CNTs for Making Epoxy/CNT Composites

Functionalization of carbon nanotubes (CNTs) with linear molecular side chains of polyphenylene ether (PPE) has been shown to be effective in solubilizing the CNTs in the solvent components of solutions that are cast to make epoxy/CNT composite films. (In the absence of solubilization, the CNTs tend to clump together instead of becoming dispersed in solution as needed to impart, to the films, the desired CNT properties of electrical conductivity and mechanical strength.) Because the PPE functionalizes the CNTs in a non-covalent manner, the functionalization does not damage the CNTs. The functionalization can also be exploited to improve the interactions between CNTs and epoxy matrices to enhance the properties of the resulting composite films.

Posted in: Briefs

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Progress Toward Sequestering Carbon Nanotubes in PmPV

A report reopens the discussion of “Sequestration of Single-Walled Carbon Nanotubes in a Polymer” (MSC-23257), NASA Tech Briefs, Vol. 31, No. 12 (December 2007), page 38. To recapitulate: Sequestration of single-walled carbon nanotubes (SWNTs) in molecules of poly(m-phenylenevinylene-co-2,5-dioctyloxy- p-phenylenevinylene) [PmPV] is a candidate means of promoting dissolution of single-walled carbon nanotubes (SWNTs) into epoxies for making strong, lightweight epoxy-matrix/carbon-fiber composite materials. Bare SWNTs cannot be incorporated because they are not soluble in epoxies. One can render SWNTs soluble by chemically attaching various molecular chains to them, but such chemical attachments weaken them. In the present approach, one exploits the tendency of PmPV molecules to wrap themselves around SWNTs without chemically bonding to them. Attached to the backbones of the PmPV molecules are side chains that are soluble in, and chemically reactive with, epoxy precursors, and thus enable suspension of SWNTs in epoxy precursors. At time of the cited prior article, there had been only partial success in functionalizing the side chains to make them sufficiently soluble and reactive. The instant report states that a method of functionalization has been developed.

Posted in: Briefs, TSP

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Improvements in Production of Single-Walled Carbon Nanotubes

Continuous mass production in fluidized-bed reactors now appears feasible. A continuing program of research and development has been directed toward improvement of a prior batch process in which single-walled carbon nanotubes are formed by catalytic disproportionation of carbon monoxide in a fluidized-bed reactor. The overall effect of the improvements has been to make progress toward converting the process from a batch mode to a continuous mode and to scaling of production to larger quantities. Efforts have also been made to optimize associated purification and dispersion post processes to make them effective at large scales and to investigate means of incorporating the purified products into composite materials. The ultimate purpose of the program is to enable the production of high-quality single-walled carbon nanotubes in quantities large enough and at costs low enough to foster the further development of practical applications.

Posted in: Briefs

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Filtering Water by Use of Ultrasonically Vibrated Nanotubes

Water molecules could flow through; larger molecules and other particles could not. Devices that could be characterized as acoustically driven molecular sieves have been proposed for filtering water to remove all biological contaminants and all molecules larger than water molecules. Originally intended for purifying wastewater for reuse aboard spacecraft, these devices could also be attractive for use on Earth in numerous settings in which there are requirements to obtain potable, medical-grade, or otherwise pure water from contaminated water supplies. These devices could also serve as efficient means of removing some or all water from chemical products — for example, they might be useful as adjuncts or substitutes for stills in the removal of water from alcohols and alcoholic beverages. These devices may be constructed using various materials, such as ceramics, metallics, or polymers, depending on end-use requirements.

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Large-Format Carbon Nanotube Sheets Fabricated With Chemical Vapor Deposition

Non-woven, textile-like sheets of carbon nanotubes can be created without post-processing. Carbon nanotube (CNT) sheets, yarns, and their derivative products are beginning to emerge in the marketplace. A productive and scalable manufacturing method utilizes a chemical vapor deposition process for making very-large-format CNT non-woven, textile-like sheets directly from the reactor without post-processing.

Posted in: Materials, Briefs

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Quantifying Airborne Hydrogen in Nearly Real Time

An indirect method of measuring small concentrations of hydrogen gas in air in nearly real time has been devised to circumvent the difficulty of performing such measurements directly. In this method, a sample of air suspected of containing hydrogen is first enclosed in a suitable container, and its humidity is measured. The enclosed sample is then exposed to ultraviolet light (typically at a wavelength of 254 nm), which photolyzes the hydrogen to water vapor. The exposure time needed for photolysis is of the order of minutes, the exact value depending on the shape and size of the sample container.

Posted in: Briefs, TSP

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