Molecular Dynamics Insight in the Tilt Effect of Carbon Nanotubes in Small Assemblies

Carbon nanotubes (CNTs) of finite length assembled in small bundles were modeled with molecular dynamics simulations. Instead of the generally considered parallel alignment of CNTs for long sizes and large assemblies, an interesting tilt angle is observed in the small hexagonal 7 CNT bundle, in which the outer 6 CNTs spirally tilt to one direction with respect to the CNT in the center. This effect was characterized with CNTs of different lengths. The tilt angle shows a strong length dependence in the short length regime and disappears at longer lengths. In addition, the tilt angle affected by CNT diameter was analyzed with CNTs of various diameters. Narrower CNTs are more parallel, while thicker ones show larger tilt angles and stronger vibrations. This tilt effect was confirmed for both armchair and zigzag type CNTs. The present work for the first time unveils the tilt effect of small CNT bundles in finite length.