(467f) Molecular-Dynamics Analysis of the Thermomechanical Behavior of Nanodiamond Superstructures in Interlayer-Bonded Twisted Bilayer Graphene

Graphene derivatives and metamaterials are usually fabricated through chemical functionalization and defect engineering of graphene sheets. These materials have potential for numerous technological applications since tailoring their nanostructure enables fine tuning of their thermomechanical properties. Toward this end, we have conducted a systematic computational study on the thermomechanical behavior of a class of two-dimensional (2D) graphene-diamond nanocomposite superstructures, formed through patterned hydrogenation-induced interlayer covalent bonding of twisted bilayer graphene with commensurate bilayers. These superstructures are fully characterized by the commensurate bilayer’s twist angle, the interlayer bond pattern, and the concentration of sp³-bonded C atoms in the nanocomposite material. The analysis of their thermomechanical behavior is based on molecular-dynamics (MD) simulations according to a reliable interatomic bond-order potential.

We report results on the mechanical behavior of such carbon nanocomposite superstructures based on MD simulations of uniaxial straining tests and establish the dependence of the superstructures’ mechanical properties on the concentration of sp³-bonded C atoms. We also demonstrate that a brittle-to-ductile transition occurs in these superstructures with increasing the concentration of sp³-bonded C atoms beyond a critical level. The underlying ductile fracture mechanism, mediated by void formation, growth, and coalescence, is characterized, and the superior mechanical response to uniaxial straining of the ductile nanodiamond superstructures is demonstrated.

Furthermore, we study the mechanical response of these superstructures to indentation and shear straining based on MD simulations of nanoindentation tests and dynamical shear straining tests. We establish the dependences of the elastic modulus, hardness, and shear strength of the superstructures on the full range of their structural parameters, especially on the fraction of diamond in the nanocomposite superstructure measured by the concentration of sp³-bonded C atoms. The resulting structural responses and fracture mechanisms of the superstructures under nanoindentation testing and shear straining also are characterized in detail. Finally, we report results for the lattice thermal conductivity of these superstructures based on non-equilibrium MD simulations of thermal transport. We find that the lattice thermal conductivity is reduced significantly with increasing concentration of sp³-bonded C atoms in the superstructures, which makes these 2D carbon nanomaterials very promising for thermal management applications.