Functionalized Graphene Origami Metamaterials

One-atom thick graphene is of great importance for next-generation thermoelectric devices, heat management systems, and flexible nanoelectronics due to its ultra-high stiffness, strength, and thermal conductivity. By employing the reverse non-equilibrium molecular dynamics method, we demonstrate that the hydrogenated graphene origami metamaterials provide a new platform for designing shape-changing graphene metamaterials with tunable thermal conductivity, tailorable strength and failure strain, and negative thermal expansion coefficients. The atomistic simulation results demonstrate that a vast range of thermal conductivity can be obtained by tailoring the topological parameters of the Miura-ori graphene origami, altering the adatom types and density, and applying mechanical strains. The comparison between the atomistic and continuum-based simulation results shows that the effect of size-dependency on the thermal conductivity can be neglected when the size is far beyond the average phonon mean free path due to the transformation of heat conduction mechanism from ballistic to diffusive transport of phonons. Further results of phonon density of states and phonon group velocity show that the softening of phonon modes and decreased phonon group velocity result in the decreased thermal conductivity of graphene origami metamaterials. Finally, 3D graphene origami metamaterials are constructed by assembling the graphene origami strips, and their thermo-mechanical performance is evaluated. The functionalized origami nanostructure proposed here presents two main differences with respect to those reported graphene metamaterials: First, the proposed graphene metamaterials are intrinsically nonporous and therefore retain high strength; the stretchability is also increased compared to the pristine graphene. Second, the thermal conductivity can be increased by applying tension and decreased by applying compression, presenting a feasible strategy for tuning the thermal conductivity of engineered nanomaterials. Our study provides a new route for designing reconfigurable graphene metamaterials with tunable thermo-mechanical properties and controllable functionalities.