Tunable thermal conductivities of graphene and graphyne under in-plane torsion

Abstract

Using the non-equilibrium molecular dynamics method, the thermal properties of two dimensional nanomaterials are investigated by considering graphene and graphyne nanosheets with circular boundaries. The thermal transport efficiency of graphene and graphyne under heat flux from the inner boundary to outer boundary is revealed to be tunable by applying in-plane torsion at the inner boundary, and the tunable range of thermal conductivity for graphyne could be up to 37% (15% for graphene). With the increase of rotation angle, the thermal conductivities of both graphene and graphyne are found to increase at small rotation angles and then decrease after the occurrence of wrinkle deformation. The maximum thermal conductivity appears at the onset of wrinkling which depends on the lattice structure and stiffness of the nanosheets. By systematically investigating the morphological characteristics and the phonon spectra under different torsion angles, the tunable thermal conductivities of both graphene and graphyne are found to be controlled by three factors including surface smoothness, stress concentration and lattice instability. The increase of thermal conductivity with small torsion angles is caused by the suppressed surface fluctuation which decreases the phonon scattering, while the wrinkling and lattice instability occurring under large torsion angles accounts for the deterioration of thermal conductivity. Since the fluctuation of graphyne is efficiently compressed at smaller torsion angles compared to graphene, the maximum thermal conductivity of graphyne appears earlier than graphene. Such correlation between out-of-plane deformation and in-plane thermal conductivity provides new insights into the thermal management of two dimensional nanomaterials.