碳纳米管的热导率:从弹道到扩散输运

采用非平衡分子动力学方法研究了300 K和1000 K时（5，5）碳纳米管热导率随长度的变化.在室温下，碳纳米管长度小于40 nm时热导率与长度呈线性关系，此时导热处于弹道输运阶段，单位面积弹道热导为5.88×10⁹ Wm^-2K^-1．随着碳纳米管长度的增加，其热导率逐渐增加，但增加速度随长度逐渐减小，此时导热处于弹道—扩散输运阶段，并随长度的增加从以弹道输运为主向以扩散输运为主转变．长度大于10 μm时由于弹道输运可以忽略，导热近似达到完全 关键词： 碳纳米管 热导率 弹道输运 低维导热

Thermal conductivity of carbon nanotube: From ballistic to diffusive transport

Length dependence of the thermal conductivity of (5, 5) carbon nanotubo at 300 K and 1000 K is studied by nonequilibrium molecular dynamics simulations. At room temperature the thermal conductivity shows linear length dependence for the tube length less than 40 nm, which shows completely ballistic transport. The calculated ballistic thermal conductance per unit area is 5.88 x 10~9 Wm~(-2)K~(-1). The thermal conductivity increases with the increase of the nanotube length, but the increase rate decreases as the length increases. It shows that the phonon transport is in the ballistic-diffusive regime, and transits from ballistic to diffusive with increase of the tube length. The thermal conduction is close to completely diffusive transport and the ballistic transport can be ignored when the nanotube is longer than 10 μm. In the simulations, the power exponent of the thermal conductivity of carbon nanotube to the tube length decreases by decaying exponential function as the tube length increases.Different from one-dimensional material, in the thermodynamic limit, a completely diffusive transport will dominate the thermal transport in carbon nanotubes, and the thermal conductivity will converge to a finite value.