Molecular Dynamics Studies On Thermal Transport Properties Of Low-dimensional Materials

Due to the special bonding environment of low-dimensional materials,the heat transfer characteristics are much different from that in bulk materials.For instance,the thermal conductivity in low-dimensional materials shows strong size effect,ballistic transport and hot rectification effect.Therefore,it is of particular importance to explore the thermal transport behavior and the corresponding mechanisms in low-dimensional materials,which is benefit for their applications in the fields related to heat transfer.In this paper,molecular dynamics is used to simulate the heat transfer behaviors of two kinds of low dimensional materials,namely,graphdiyne and polyethylene.Specifically,we discussed the effects of chirality,side chain and strain on the thermal conductivity and phonon transmission of two systems.The main conclusions are as follows:(1)Different two dimensional graphdiyne were studied using non-equilibrium molecular dynamics,the size effect of the different acetylene number and multilayer graphdiyne.With acetylene number increases,the thermal conductivity of graphdiyne shows slow convergence.The size effect of multilayer graphdiyne thermal conductivity will also change,with layer number of the increase,the thermal conductivity shows faster convergence.Through dispersion relations,group velocity and the analysis of the spectrally decomposed heat current,we found that when the acetylene increase,it makes the system low frequency phonon heat transfer dominates,so induce the size effect.And interlayer van der Waals anharmonic scattering effects in multilayer graphdiyne system under 12 THz phonons,makes the thermal transfer properties change.(2)Quasi one-dimensional graphdiyne nanoribbon don't show thermal conductivity with the length of the index divergent phenomenon,but with boundary dependencies.Moreover,by adding atomic side chain on the edge of nanoribbon,which will further reduce the nanoribbon thermal conductivity,this is mainly due to side chain will lead to additional phonon resonance effect.In addition,one dimensional zigzag graphdiyne nanoribbon,armchair graphdiyne nanoribbon with strain have different response.By spectrally decomposed heat current analysis of strain is mainly due to the different response under 4 THz frequency phonons,which affect the change of thermal transfer in graphdiyne nanoribbon.(3)Using non-equilibrium and equilibrium molecular dynamics method to study the thermal transfer process of polyethylene system,considering the lattice strain and rotation mode of one dimensional system model,found that polyethylene single chain thermal conductivity does not exist divergence trend,according to the size of extrapolation to get its intrinsic thermal conductivity is 80.6 W/mK.When polyethylene chain form polyethylene fiber,due to the interaction between the chain and structure order degree is reduced,the thermal conductivity is lower than single thermal conductivity and reduce with the increase of fiber radius.The current research not only provides a clear picture on the phonon transport mechanism in low dimensional materials,but also gives a theoretical reference for thermal conductivity design in the fields like thermoelectric materials and thermal interface materials...