空位结构缺陷对C纳米管弹性性质的影响

用分子动力学方法对不同空位缺陷的扶手椅型与锯齿型单壁C纳米管杨氏弹性模量进行了计算和分析. 结果表明：扶手椅型（5, 5）, （10,10）和锯齿型（9, 0）, （18, 0） 纳米管在无缺陷时其杨氏模量分别为948,901和804,860 GPa. 随管径的增大，扶手椅型和锯齿型单壁C纳米管弹性模量分别减小和增大，表现出完全不同的变化规律. 随着C纳米管中单点空位缺陷的均匀增加，杨氏模量下降，当缺陷比率增加到一定程度时，杨氏模量下降骤然趋缓，形成一下降平台；双空位缺陷对C纳米管杨氏模量的影响与其分布方向有关；随单点空位缺陷间原子数的增加，在轴向上，杨氏模量下降到某一值小幅波动，而在周向上杨氏模量先下降，然后上升到某一稳定值. 随两单点空位缺陷的空间距离进一步增大，杨氏模量又呈微降趋势. 通过分子间σ键与π键特征及缺陷间近程电子云耦合作用规律与空位缺陷内部5-1DB缺陷的形成特点等理论对上述规律进行了分析. 关键词： 空位缺陷 C纳米管 分子动力学 杨氏模量

Effects of vacancy structural defects on the elastic properties of carbon nanotubes

The molecular dynamics method is used in this paper to investigate the effect of vacancy defects on the elastic properties of armchair and zigzag single walled carbon nanotubes （SWCNTs）.The results show that the Young's moduli of armchair （5,5）, （10,10） and zigzag （9,0）, （18,0） single walled carbon nanotubes are 948, 901 GPa, and 804, 860 GPa,respectively. The armchair and the zigzag SWCNTs Young's moduli decrease and increase with the increase of the nanotubes' diameter, respectively. With the increase of the vacancy defect ratio, the Young's moduli will decrease. When the vacancy defect achieves a certain ratio, there appears a sudden slow down in the curves of Young's modulus vs. vacancy defect ratio and a platform emerges. The influence of the bi vacancy defects on the Young's moduli of the carbon nanotubes depends on the orientation of the defects. As the number of atoms between the two single vacancy defects increases, when the defects are located in the direction of the axis, the Young's modulus decreases to certain value and fluctuates around it; but when the defects are located in the direction of the circumference, the Young's modulus decreases first, then ascends and finally tends to a constant, and the Young's moduli will decrease a little with increasing of the distance between the two singlevacancies. The reasons are analyzed by considering the features of the bond σ and bond π between the molecules and the theory of the short range coupling of the electron clouds between two defects as well as the theory of 5 1DB defect formation in the vacancy defects.