Jul 20, 2014
Limiting 'wiggle room' increases carbon chain stiffness
Carbyne is a one-dimensional (1D) chain of single- and triple-bonded carbon atoms. Predicted to be one of the strongest materials in existence, it has a specific strength and a Young's modulus exceeding that of steel, titanium and even diamond or graphene. However, the exemplary strength and stiffness only arise from loading in tension, i.e. when the chain is pulled apart rather than pushed together. Through a computational material science approach and reporting in Nanotechnology, researchers at Northeastern University have found a way to strengthen and control this behaviour in compression.
It is well known in structural engineering that buckling can be prevented by bracing a column along its length. By preventing the lateral motion of a column, the buckling strength increases and additional load can be sustained in compression. Discretely bracing a carbyne chain, however, is not possible. As an alternative, carbyne chains have been observed within the centre cavity of carbon nanotubes. The diameter of carbon nanotubes can vary, providing a potential range to confine or brace a carbyne chain, and thus control the compressive behaviour.
With this hypothesis, the researchers use molecular dynamics simulations to probe the effect of confinement on the compressive stiffness of carbyne chains at finite temperatures. Inspired by carbon nanotubes, carbyne chains of various lengths (65 Å to approximately 120 Å) are confined within an idealized cylindrical rigid enclosure with diameters varying from 0.1 Å to 4.2 Å. The carbyne chains are then compressed, and the potential energy of the system tracked along with the end-to-end distance and deformation.
This energy versus deformation provides the necessary data to fit the behaviour of a harmonic or linear spring. These fits provide an "effective spring stiffness" that can be varied over an order of magnitude (from less than 1 kcal/mol/ Å2 to more than 50 kcal/mol/ Å2) as a function of both chain length (L) and carbyne confinement (D). The trend is clear – as the "wiggle room" of the chain is decreased (either by chain length or cylindrical radius), the effective compressive stiffness increases.
While carbyne has a single material stiffness in tension, the researchers have clearly shown that compressive stiffness (due to the onset of buckling) is a system or geometric property, with the ability to be tuned or varied. Using carbyne as a building block, the compressive stiffness can be actively designed and exploited in applications such as molecular sensors, tunable nanodampers or other nanodevices.
The researchers published their work in the journal Nanotechnology 25 335709 (IOPselect article).
Graphyne: a two-dimensional material with thermoelectric properties (May 2014)
Manipulating boron-nitride nanotubes unconventionally (May 2014)
Studies of defects in boron nitride reveal useful properties for devices (Jan 2014)
About the author
Ashley Kocsis is a graduate student in Steven W Cranford’s Laboratory for Nanotechnology In Civil Engineering (NICE) in the Department of Civil and Environmental Engineering (CEE) at Northeastern University. Neta Aditya Reddy Yedama, also a graduate student with the CEE department at Northeastern, was a volunteer lab member. The NICE Lab undertakes multiscale investigations to both apply structural mechanics approaches to nanoscale systems and exploit material phenomena in civil engineering infrastructure.