Thermal conductivities of graphyne nanotubes from atomistic simulations

• Thermal conductivities of graphyne-n nanotubes are calculated by RNEMD simulations.
• TC decreases with the increase of the generation number n   and scales as λ∼n-0.57λ∼n-0.57.
• TC has a weak dependence on diameter and scales as λ∼d0.03λ∼d0.03 at larger diameters.
• TCs of GNT-n are two orders of magnitude smaller than that of CNT at μm scale.

Thermal conductivities (TCs) of graphyne-n nanotubes (GNT-n) are investigated by reverse non-equilibrium molecular dynamics simulations. Dependences of the generation number n, diameter d, and length L on TCs of GNT-n are derived with scaling relations and explained from the analysis of phonon density of states. Simulation results reveal that with the increase of the generation number n  , TC decreases and scales as λ∼n-0.57λ∼n-0.57. The diameter d   has a weak impact on TC and a universal scaling law of λ∼d0.03λ∼d0.03 at d > 5 nm is derived for all GNT-n. With the increase of the length, the scaling relation between TC and L has a crossover. After the crossover, the scaling exponents are 0.16, 0.07, 0.05, 0.04, 0.03 for n = 1–5, respectively, which are much smaller than the scaling exponent of 0.48 for the carbon nanotube (CNT). TC values of GNT-n are estimated to be 92.4, 43.6, 30.4, 27.4, 23.0 W/(m K) for n = 1–5, respectively, at L = 2.6 μm by extrapolation, which are two orders of magnitude smaller than 2820.6 W/(m K) of the CNT with the same length. This implies the graphyne-n nanotubes may be more promising thermoelectric materials than the CNT.

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