Nanoscale elasticity of highly anisotropic pyrocarbons

We report on the elastic properties of high-textured laminar pyrocarbons (PyCs) as obtained at the nanoscale using atomistic simulations on realistic models of the rough laminar (RL) PyC, the regenerative laminar (ReL) PyC, and the ReL PyC heat treated at temperatures up to 1700 °C. The purely longitudinal (C11,C12,C66,E1 and ν12) and transverse (C33 and E3) elastic properties of such materials have values of around 50-75% of those found for graphite. Conversely, cross longitudinal-transverse properties (C13,C44,ν13 and ν31) are much larger in PyCs than in graphite (up to around one order of magnitude for ν31). Our results also show that stiffness decreases with the hydrogen content, that longitudinal properties increase with the extent of graphene domains and decrease with the misorientation of the layers, and that transverse and cross properties significantly increase with the amount of interlayer cross-links present in the materials. Comparison to known experimental data indicates that texture effect at superior scales play an important role in the effective macroscopic elasticity constants. Finally, from a materials perspective and in agreement with the structural evolution, the elastic properties of the ReL PyC evolve with heat treatment towards those of the RL PyC.