Approach-to-equilibrium molecular dynamics simulations have been used tostudy thermal transport in nanocrystalline graphene sheets. Nanostructuredgraphene has been created using an iterative process for grain growth frominitial seeds with random crystallographic orientations. The resulting cellshave been characterized by the grain size distribution based on the radius ofgyration, by the number of atoms in each grain and by the number of atoms inthe grain boundary. Introduction of nanograins with a radius of gyration of 1nm has led to a significant reduction in the thermal conductivity to 3% of thevalue in single crystalline graphene. Analysis of the vibrational density ofstates has revealed a general reduction of the vibrational intensities andbroadening of the peaks when nanograins are introduced which can be attributedto phonon scattering in the boundary layer. The thermal conductivity has beenevaluated as a function of the grain size with increasing size up to 14 nm andit has been shown to follow an inverse rational function. The grain sizedependent thermal conductivity could be approximated well by a function wheretransport is described by a connection in series of conducting elements andresistances (at boundaries).
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