Unexpected anisotropy of (14,14,14)-Graphyne: A comprehensive study on the thermal transport properties of graphyne based nanomaterials

By performing molecular dynamics, the thermal transport properties of seven type graphyne (GY) with different structures (nanosheet, nanotube and GY/graphene (GR) heterojunction) are investigated. It can be observed comparing with other six GY, the thermal conductivity (TC) of (14,14,14)-GY shows unexpectedly significant anisotropy, which is consistent with previous study in Phys. Chem. Chem. Phys. 2016, 18, 24210. This anisotropy is mainly due to the lower contribution of high-frequency and short-wavelength phonons weakened by armchair (14,14,14)-GY. Moreover, when GY is rolled up to GY nanotubes (NTs), it is interesting to discover TC of GYNT, especially (14,14,14)-GYNT, shows a diameter-dependent anisotropy. For large-diameter NT, the TC of zigzag model is higher, however, an opposite phenomenon is obtained with small-diameter model. This phenomenon can be explained by the relative alternation of phonon group velocity and phonon lifetime and the appearance of band gap with the change of diameter. At last, we also notice the GY/GR heterojunctions express much lower thermal resistance (TR) comparing with other carbon based heterojunctions, and the in-plane TR of GY/GR heterojunction is two orders of magnitude lower than that of out-of-plane TR. Further, the alternation of TR can be well explained by the coupling degree of different type phonons. (C) 2018 Elsevier Ltd. All rights reserved.