New record for longest linear carbon chain

An international research team has created the longest linear carbon chain to date by linking more than 6,000 carbon atoms into a single-file strand that stretches for nearly a micrometer (Nat. Mater. 2016, DOI: 10.1038/nmat4617).

The previous record stood at around 100 carbon atoms, making the new result the closest approximation scientists have to carbyne, one of the world’s more contentious materials, says team leader Thomas Pichler of the University of Vienna.

Theoretically, carbyne is an infinite line of carbon atoms, strung together with alternating single and triple bonds, with higher strength and stiffness than carbon’s multidimensional allotropes: graphene, nanotubes, and diamond. But real linear carbon chains are prone to cross-link explosively. This instability and a litany of substances misidentified as carbyne have led to hot disputes when new claims of carbyne arise.

Pichler and his team deliberately dubbed their creations “long, linear carbon chains” and addressed the instability problem by growing their chains inside protective carbon nanotubes. The researchers annealed empty double-walled tubes with specific inner diameters—about 0.7 nm—under high vacuum to bolster formation of linear carbon chains. The team thus created much longer chains and many more of them compared with previous efforts, Pichler says.

This is an exciting study, says Hisanori Shinohara, a nanocarbon chemist at Nagoya University. “The next important and definitely required step is to extract the linear chain molecules from the carbon nanotubes” to understand their properties, he adds.