Rivera José L, McCabe Clare, Cummings Peter T
Department of Chemical Engineering, Universidad Michoacana de San Nicolás de Hidalgo, Santiago Tapia No. 403, Colonia Centro, Morelia, Michoacan 58000, Mexico.
Nanotechnology. 2005 Feb;16(2):186-98. doi: 10.1088/0957-4484/16/2/003. Epub 2004 Dec 23.
The mechanical properties of sliding carbon nanotubes have been investigated by classical molecular dynamics simulations in the canonical ensemble. In particular we have studied damped oscillations in the separation between the centres of mass of the inner and outer tubes of double-walled carbon nanotubes (DWCN). Incommensurate DWCNs forming (7, 0)@(9, 9) structures were simulated for systems at 298.15 K with axial lengths from 12.21 to 98.24 nm. The oscillations exhibited frequencies in the range of gigahertz with the frequency decreasing as the length of the system increases. The time until oscillations become negligible exhibited a nearly linear dependence on the length of the system. Two macroscopic models were developed in order to understand the forces involved in terms of macroscopic properties like friction and shear. The first model considered constant restoring forces during the whole event, while in the second the value of these constant restoring forces depended on the initial conditions of each oscillation. Both models reproduced the oscillations quite well, while the second model allows us to predict the dynamic shear strength in terms of the axial length of the system for tubes with the same diameters. The calculated dynamic shear strength exhibited monotonic behaviour with an inverse dependence on the length of the system. For systems with unequal axial lengths, the restoring force, which drives the oscillation, is reduced compared to the system with equal lengths, regardless of whether the outer nanotube is longer or shorter.
通过正则系综中的经典分子动力学模拟研究了滑动碳纳米管的力学性能。特别是，我们研究了双壁碳纳米管（DWCN）内外管质心之间间距的阻尼振荡。对形成（7, 0）@（9, 9）结构的非公度DWCN在298.15 K下进行模拟，系统轴向长度从12.21至98.24 nm。振荡频率在吉赫兹范围内，且频率随系统长度增加而降低。振荡变得可忽略不计所需的时间与系统长度呈现近似线性关系。为了从摩擦和剪切等宏观性质方面理解其中涉及的力，开发了两个宏观模型。第一个模型在整个过程中考虑恒定的恢复力，而在第二个模型中，这些恒定恢复力的值取决于每次振荡的初始条件。两个模型都能很好地再现振荡，而第二个模型使我们能够根据具有相同直径的管的系统轴向长度预测动态剪切强度。计算得到的动态剪切强度呈现单调行为，与系统长度成反比。对于轴向长度不等的系统，驱动振荡的恢复力与长度相等的系统相比会减小，无论外纳米管是更长还是更短。
