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From:
http://www.ineffableisland.com/2010/06/carbon-nanotube-super-compressible.html
The blogger, Alton Parrish, writes:
“Carbon Nanotube Super-Compressible Foams Used in Actuators and Coatings For Mechanical Damping And Energy Absorbing Systems”
“Rensselaer Polytechnic Institute (Troy, NY) earned U.S. Patent 7,727,624 for super-compressible carbon nanotube films and micro-bundles. The open-cell nature of the nanotube foam provides excellent breathability with a high strength-to-weight ratio, dimensional stability at elevated temperature or humidity, and resistance to chemical environments.”
“Nanotube foams are used in a number of applications, for instance, in flexible electromechanical systems, or as compliant interconnect structures, actuators and coatings for mechanical damping and energy absorbing systems. The nanotubes foams are available for licensing from RPI's Office of Technology Commercialization.”
“An open-cell carbon nanotube foam is made of a plurality of separated carbon nanotubes. The foam exhibits a Poisson's ratio substantially equal to zero, a compressibility of at least 85%, a recovery rate of at least 120 mm/min, a compressive strength of at least 12 MPa, a sag factor of at least 4, a fatigue resistance to no more than 15% permanent deformation when subjected to at least 1,000 compressive cycles at a strain of 85%, and/or a resilience of between 25% and 30%. The carbon nanotubes may be multiwalled carbon nanotubes that are aligned parallel to a thickness of a film comprising the foam, according to inventors Anyuan Cao and former RPI Professor of Engineering Pulickel Ajayan, leader of the carbon nanotube research group. Professor Ajayan is now at Rice University.
“These nanotubes can be squeezed to less than 15 percent of their normal lengths by buckling and folding themselves like springs,” says Anyuan Cao, who did much of the work as a postdoctoral researcher in Ajayan’s lab and is now assistant professor of mechanical engineering at the University of Hawaii at Manoa. “After every cycle of compression, the nanotubes unfold and recover, producing a strong cushioning effect.”
When compared with conventional foams designed to sustain large strains, nanotube foams recovered very quickly and exhibited higher compressive strength. The thickness of the nanotube foams decreased slightly after several hundred cycles, but then stabilized and remained constant, even up to 10,000 cycles. Nanotubes also are stable in the face of extreme chemical environments, high temperatures, and humidity
The three schematics in FIG. 1A illustrate, from left to right: (1) an aligned nanotube foam having an initial cross-sectional film thickness equal to the free length of the carbon nanotubes; (2) the foam under a compressive load applied along the nanotube axes, wherein the nanotubes collectively buckle to form an aligned zigzag pattern; and (3) the foam upon release of the compressive load after 1000 loading cycles whereby the foam recovers approximately 85% of the original film thickness and retains the zigzag pattern at the lower portion of the film.
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