Simulation of nanomechanics of an inner carbon nanotube in double-walled nanotube

抄録

Introduction

Carbon nanotubes (CNTs) have excellent mechanical properties such as lightweight, strength, and elasticity. These mechanical properties make CNTs promising materials as nanodevices. However, on the nanoscale, nanodevices are subject to fracture due to frictional forces because of the enhanced surface effect. To solve these problems, it is necessary to study mechanics of CNTs on the nanoscale. In this study, double-wall CNT (DWCNT) is discussed in order to elucidate the mechanical properties of CNTs. Molecular mechanics simulation for rotation of the inner tubes of DWCNT is performed. The relationship between the stacking structure of the inner and outer tubes of DWCNT and the interaction energy was analyzed to reveal the nanomechanics of the inner-layer tube.

Model and method of simulation

In this work, the rigid DWCNT comprised of the inner tube ( (3,3) armchair-type single-walled CNT (SWCNT)) and the outer tube ( (7,7) armchair-type SWCNT), was adopted as the simulation model. The models of SWCNTs were created by structural optimization using the conjugate gradient method.

Simulated results

As shown in Figure 1(a), the interaction energy of the DWCNTs showed a periodicity of about 17° with respect to the rotation angle of the inner-layer CNT. The interaction energy took the minimum values at θ=4°, 21°, 38°, 55°, 72°, ... and the maximum values at θ=12°, 30°, 47°, 64°, 81°, ... . The above simulated results can be explained by focusing on the coaxial cylindrical structure of DWCNT.

Discussions

As illustrated in Figure 1(b), the inner- and outer-layer CNTs are hexagonal and 14-square prisms, respectively. Therefore, when the inner-layer hexagonal prism rotates, the set of the planes facing parallel to each other changes between the inner-layer hexagonal and the outer-layer 14-square prisms. Therefore, the planes of the inner- and outer-layer CNTs become parallel to each other every 8.6°of rotation angle of the inner-layer CNT. Furthermore, when the inner- and outer-planes become parallel, the lattice stacking between the inner and outer planes becomes the same every about 17°. Thus the simulated results can be explained by the periodicity of the geometry and lattice stacking of DWCNT for the rotation of the inner-layer CNT.

Conclusions

In this study, the relation between the interaction energy of DWCNT and its structure was clarified as a function of the rotation angle of the inner-layer CNT. The interaction energy was found to reflect the structural information such as geometry and lattice stacking between the inner- and outer-layer CNTs.