Carbyne calculated to be 28 to 36% stronger than Graphene and twice as stiff

August 16, 2013

 A new form of carbon, carbyne, is calculated to be twice as stiff as carbon nanotubes or graphene and about significantly stronger than graphene, carbon nanotubes and diamond.

Rice University researchers calculate that it takes around 10 nanoNewtons to break a single strand of carbyne.

Carbyne specific strength 6.0–7.5×10^7 N∙m/kg
Graphene specific strength 4.7–5.5×10^7 N∙m/ kg (Carbyne 28-36% stronger)
carbon nanotubes specific strength 4.3–5.0×10^7 N∙m/ kg (Carbyne 40-50% stronger)
diamond specific strength 2.5–6.5×10^7 N∙m/kg (Carbyne 15-140% stronger)

Carbyne has other interesting properties too. Its flexibility is somewhere between that of a typical polymer and double-stranded DNA. And when twisted, it can either rotate freely or become torsionally stiff depending on the chemical group attached to its end.

Perhaps most interesting is the Rice team’s calculation of carbyne’s stability. They agree that two chains in contact can react but there is an activation barrier that prevents this happening readily. “This barrier suggests the viability of carbyne in condensed phase at room temperature on the order of days,” they conclude.

ABSTRACT -
Rice University report an extensive study of the properties of carbyne using first-principles calculations. We investigate carbyne's mechanical response to tension, bending, and torsion deformations. Under tension, carbyne is about twice as stiff as the stiffest known materials and has an unrivaled specific strength of up to 7.5*10^{7} Nm/kg, requiring a force of ~10 nN to break a single atomic chain. Carbyne has a fairly large room-temperature persistence length of about 14 nm. Surprisingly, the torsional stiffness of carbyne can be zero but can be `switched on' by appropriate functional groups at the ends. We reconstruct the equivalent continuum-elasticity representation, providing the full set of elastic moduli for carbyne, showing its extreme mechanical performance (e.g. a Young's modulus of 32.7 TPa with an effective mechanical thickness of 0.772 {\AA}). We also find an interesting coupling between strain and band gap of carbyne, which is strongly increased under tension, from 3.2 to 4.4 eV under a 10% strain. Finally, we study the performance of carbyne as a nanoscale electrical cable, and estimate its chemical stability against self-aggregation, finding an activation barrier of 0.6 eV for the carbyne-carbyne cross-linking reaction and an equilibrium cross-link density for two parallel carbyne chains of 1 cross-link per 17 C atoms (2.2 nm).