Theoretical strength and rubber-like behaviour in micro-sized pyrolytic carbon.

The creation of materials with a combination of high strength, substantial deformability and ductility, large elastic limit and low density represents a long-standing challenge, because these properties are, in general, mutually exclusive. Using a combination of two-photon lithography and high-temperature pyrolysis, we have created micro-sized pyrolytic carbon with a tensile strength of 1.60 ± 0.55 GPa, a compressive strength approaching the theoretical limit of ~13.7 GPa, a substantial elastic limit of 20-30% and a low density of ~1.4 g cm-3. This corresponds to a specific compressive strength of 9.79 GPa cm3 g-1, a value that surpasses that of nearly all existing structural materials. Pillars with diameters below 2.3 μm exhibit rubber-like behaviour and sustain a compressive strain of ~50% without catastrophic failure; larger ones exhibit brittle fracture at a strain of ~20%. Large-scale atomistic simulations reveal that this combination of beneficial mechanical properties is enabled by the local deformation of 1 nm curled graphene fragments within the pyrolytic carbon microstructure, the interactions among neighbouring fragments and the presence of covalent carbon-carbon bonds.