According to scientists at Rice University, a material called carbyne will be the strongest material if and when anyone can make it in bulk.
Carbyne is a chain of carbon atoms held together by either double or alternating single and triple atomic bonds. That makes it a true one-dimensional material, unlike atom-thin sheets of graphene that have a top and a bottom or hollow nanotubes that have an inside and outside.
According to calculations reported in the journal ACS Nano, carbyne’s tensile strength – the ability to withstand stretching – surpasses that of any other known material and is double that of graphene.
It has twice the tensile stiffness of graphene and carbon nanotubes and nearly three times that of diamond. Stretching carbyne as little as 10 percent alters its electronic band gap significantly. The material is stable at room temperature, largely resisting crosslinks with nearby chains.
“You could look at it as an ultimately thin graphene ribbon, reduced to just one atom, or an ultimately thin nanotube. It could be useful for nanomechanical systems, in spintronic devices, as sensors, as strong and light materials for mechanical applications or for energy storage,” said study senior author Dr Boris Yakobson.
“Regardless of the applications, it’s very exciting to know the strongest possible assembly of atoms.”
“Based on the calculations, carbyne might be the highest energy state for stable carbon. People usually look for what is called the ‘ground state,’ the lowest possible energy configuration for atoms. For carbon, that would be graphite, followed by diamond, then nanotubes, then fullerenes. But nobody asks about the highest energy configuration. We think this may be it, a stable structure at the highest energy possible.”
Theories about carbyne first appeared in the 19th century, and an approximation of the material was first synthesized in the USSR in 1960. Carbyne has since been seen in compressed graphite, has been detected in interstellar dust and has been created in small quantities by experimentalists.
“I have always been interested in the stability of ultimately thin wires of anything and how thin a rod you could make from a given chemical. We had a paper 10 years ago about silicon in which we explored what happens to silicon nanowire as it gets thinner. To me, this was just a part of the same question,” Dr Yakobson explained.
The researchers were aware of a number of studies that described one property or another of carbyne. They set out to detail carbyne with computer models using first-principle rules to determine the energetic interactions of atoms.
“Our intention was to put it all together, to construct a complete mechanical picture of carbyne as a material. The fact that it has been observed tells us it’s stable under tension, at least, because otherwise it would just fall apart,” said co-author Dr Vasilii Artyukhov.
The team was surprised to find that the band gap in carbyne was so sensitive to twisting.
“It will be useful as a sensor for torsion or magnetic fields, if you can find a way to attach it to something that will make it twist. We didn’t look for this, specifically; it came up as a side product. That’s the good thing about studying things carefully,” Dr Artyukhov said.
Another finding of great interest was the energy barrier that keeps atoms on adjacent carbyne chains from collapsing into each other.
“When you’re talking about theoretical material, you always need to be careful to see if it will react with itself. This has never really been investigated for carbyne.”
“The literature seemed to indicate carbyne was not stable and would form graphite or soot.”
Instead, the researchers found carbon atoms on separate strings might overcome the barrier in one spot, but the rods’ stiffness would prevent them from coming together in a second location, at least at room temperature.
“Bundles might stick to each other, but they wouldn’t collapse completely,” Dr Yakobson said.
“That could make for a highly porous, random net that may be good for adsorption. The nominal specific area of carbyne is about five times that of grapheme,” Dr Artyukhov added.
Bibliographic information: Mingjie Liu et al. Carbyne from First Principles: Chain of C Atoms, a Nanorod or a Nanorope. ACS Nano, published online October 05, 2013; doi: 10.1021/nn404177r