Chen Haibin, Johnson J Karl, Sholl David S
Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
J Phys Chem B. 2006 Feb 9;110(5):1971-5. doi: 10.1021/jp056911i.
Molecular dynamics simulations of rigid, defect-free single-walled carbon nanotubes have previously suggested that the transport diffusivity of gases adsorbed in these materials can be orders of magnitude higher than any other nanoporous material (A. I. Skoulidas et al., Phys. Rev. Lett. 2002, 89, 185901). These simulations must overestimate the molecular diffusion coefficients because they neglect energy exchange between the diffusing molecules and the nanotube. Recently, Jakobtorweihen et al. have reported careful simulations of molecular self-diffusion that allow nanotube flexibility (Phys. Rev. Lett. 2005, 95, 044501). We have used the efficient thermostat developed by Jakobtorweihen et al. to examine the influence of nanotube flexibility on the transport diffusion of CH4 in (20,0) and (15,0) nanotubes. The inclusion of nanotube flexibility reduces the transport diffusion relative to the rigid nanotube by roughly an order of magnitude close to zero pressure, but at pressures above about 1 bar the transport diffusivities for flexible and rigid nanotubes are very similar, differing by less than a factor or two on average. Hence, the transport diffusivities are still extremely large compared to other known materials when flexibility is taken into account.
此前，对刚性、无缺陷的单壁碳纳米管进行的分子动力学模拟表明，吸附在这些材料中的气体的传输扩散率可能比任何其他纳米多孔材料高出几个数量级（A. I. 斯库利达斯等人，《物理评论快报》，2002年，第89卷，第185901页）。这些模拟必定高估了分子扩散系数，因为它们忽略了扩散分子与纳米管之间的能量交换。最近，雅各布托魏亨等人报告了对分子自扩散的精细模拟，该模拟考虑了纳米管的柔韧性（《物理评论快报》，2005年，第95卷，第044501页）。我们使用雅各布托魏亨等人开发的高效恒温器，研究了纳米管柔韧性对CH4在（20,0）和（15,0）纳米管中传输扩散的影响。在接近零压力时，考虑纳米管的柔韧性会使传输扩散相对于刚性纳米管降低大约一个数量级，但在高于约1巴的压力下，柔性和刚性纳米管的传输扩散率非常相似，平均相差不到两倍。因此，当考虑柔韧性时，与其他已知材料相比，传输扩散率仍然极大。
