Pound for pound, carbon nanotubes are stronger and lighter than steel, but unlike other materials, the miniscule cylinders of carbon – which are no wider than a strand of DNA – remain remarkably robust even when chunks of their bodies are blasted away with heat or radiation. A new study by Rice University scientists offers the first explanation: tiny blemishes crawl over the skin of the damaged tubes, sewing up larger holes as they go.
"The shape and direction of this imperfection does not change, and it never gets any larger," said lead researcher Boris Yakobson, professor of mechanical engineering and materials science and of chemistry. "We were amazed by it, but upon further study we found a good explanation. The atomic irregularity acts as a kind of safety valve, allowing the nanotube to release excess energy, in much the way that a valve allows steam to escape from a kettle."
The research appears Feb. 16 issue of in Physical Review Letters.
Carbon nanotubes are hollow cylinders of pure carbon that measure about a billionth of a meter, or one nanometer, across. They are much longer than they are wide, akin in shape to 100-foot garden hose, and they're 100 times stronger than steel at one-sixth the weight.
The carbon atoms in nanotubes are joined together in six-sided hexagons, so when scientists sketch out the arrangement on paper, nanotubes look something like a rolled up tube of chicken wire. Yakobson's "smart repair machine" is a deformity, a blemish in this pattern. The blemish consists of a five-sided pentagon joined to a seven-sided heptagon and contains a total of ten atoms. Yakobson, who specializes in using computers to decipher the atomic pecularities of materials, discovered several years ago that mechanically stressed nanotubes – like those being pulled very hard from both ends – are predisposed to develop these 5/7-defects due to the complex interplay of thermodynamic forces at work in the nanotube.
In the latest study, Yakobson, research associate Feng Ding and students examined the effects of other types of stress, including exposure to heat and radiation. The tests confirmed the predisposition of nanotubes to develop the 5/7 blemishes, and they revealed the blemishes' unexpected healing powers.
"The 5/7-blemishes move across the surface of the nanotube like a steamship, giving off puffs of carbon gas," said Ding. "In their wake, the skin of the tube appears pristine, in its characteristic hexagonal arrangement."
Yakobson said the blemishes consume all larger defects, and chug along indefinitely, rearranging atoms and healing the skin of the damaged nanotubes. This explains how nanotubes retain their strength, even when severely damaged. But the healing comes with a price.
"In their role as a safety valve, the 57-steamers give off energy and mass, which is released as pairs of gaseous carbon atoms," Yakobson said. "Since they never change shape or stop moving, they ever so slowly eat away the surface of the nanotube, one pair of atoms at a time."
Yakobson said the 5/7-blemishes turn when they reach the end of the nanotube and return in the opposite direction. In fact, there's only one thing that can stop them: another 5/7 blemish. If two of the blemishes run headlong into one other, they cancel each other out and disappear.
Jade Boyd | EurekAlert!
X-ray photoelectron spectroscopy under real ambient pressure conditions
28.06.2017 | National Institutes of Natural Sciences
New photoacoustic technique detects gases at parts-per-quadrillion level
28.06.2017 | Brown University
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
28.06.2017 | Physics and Astronomy
28.06.2017 | Physics and Astronomy
28.06.2017 | Health and Medicine