Xingming Guo

Chirality- and size-dependent elastic properties of single-walled carbon nanotubes

An analytical molecular mechanics model is established to relate the chirality- and size-dependent elastic properties of a single-walled carbon nanotube to its atomic structure. Properties at different length scales are directly connected by the derived closed-form expressions. The effects of tube chirality and tube diameter are investigated. The present analytical results are helpful to the understanding of elastic properties of carbon nanotubes, and thus are important for the application of carbon nanotubes as building blocks of nanomechanical devices.

Prediction of chirality- and size-dependent elastic properties of single-walled carbon nanotubes via a molecular mechanics model

Molecular mechanics has been widely used to analytically study mechanical behaviour of carbon nanotubes. However, explicit expressions for elastic properties of carbon nanotubes are so far confined to some special cases due to the lack of fully constructed governing equations for the molecular mechanics model. In this paper, governing equations for an analytical molecular mechanics model are fully established. The explicit expressions for five in-plane elastic properties of a chiral single-walled carbon nanotube are derived, which make properties at different length-scales directly connected. The effects of tube chirality and tube diameter are investigated. In particular, the present results show that the classic relationship from the isotropic elastic theory of continuum mechanics between Youngs modulus and shear modulus of a single-walled carbon nanotube is not retained. The present analytical results are helpful to the understanding of elastic properties of carbon nanotubes, and also useful to the topic of linking molecular mechanics with continuum mechanics.

Reversible mechanical bistability of single-walled carbon nanotubes under axial strain

Using Brenner’s second generation reactive empirical bond order potential, we show by molecular dynamics that the single-walled carbon nanotube with a diameter of about 5nm under axial strain possesses excellent reversible mechanical bistability. This feature provides a high potential of using only one single-walled carbon nanotube to realize bistate functions in nanomechanical systems which will benefit from smaller size significantly.

The effects of an inserted linear carbon chain on the vibration of a carbon nanotube

An elastic string–elastic shell model is developed to study the coupled vibration of a carbon nanowire made of a linear carbon chain (C-chain) inserted inside a carbon nanotube (CNT). It is shown that the vibration of the inserted C-chain is coupled with vibration of the CNT only for vibration modes with circumferential wavenumber n = 1. In other cases, such as axisymmetric modes (n = 0) or higher-order vibration modes with n≥2, total resultant van der Waals (vdW) force acting on the C-chain due to the innermost tube always vanishes, and therefore vibration of the CNT does not cause vibration of the inserted C-chain, although the existence of the C-chain does have an effect on the vibration of the CNT through the chain–CNT vdW forces acting on the innermost tube. The present model predicts that non-coaxial vibration between the C-chain and the innermost tube does not occur due to negligible bending rigidity of the C-chain. In addition, it is found that the C-chain has most significant effect on the lowest frequency associated with the radial vibration mode for circumferential wavenumber 2 (n = 2). In particular, the effect of the C-chain on the axisymmetric radial breathing frequencies (n = 0) predicted by the present model is found to be in reasonable agreement with known experimental and modeling results available in the literature. The present work offers systematic modeling results on the effects of an inserted C-chain on the vibration of CNTs.

Modeling of nanostructured polymer-metal composite for thermal interface material applications

Previous studies have discovered a unique type of nanostructured polymer-metal composite for thermal interface material with effective thermal conductivity of 8 W/mK. It is a promising result but extensive efforts are still required to further enhance the thermal conductivity. Therefore, this paper will try to help the process with modeling and simulation. Calculations reveal the alignment of the fibers have insignificant influence. Therefore volume percentages of fiber together with mean interface temperature become the dominating parameters of effective thermal conductivities of thermal interface material. Based on this approximation, simulation was taken which showed good results in comparison with experimental data. However, the preferred volume percentage of fibers (33%) was slightly too large according to the surface image of thermal interface material.

Detecting single molecules inside a carbon nanotube to control molecular sequences using inertia trapping phenomenon

Here we show the detection of single gas molecules inside a carbon nanotube based on the change in resonance frequency and amplitude associated with the inertia trapping phenomenon. As its direct implication, a method for controlling the sequence of small molecule is then proposed to realize the concept of manoeuvring of matter atom by atom in one dimension. The detection as well as the implication is demonstrated numerically with the molecular dynamics method. It is theoretically assessed that it is possible for a physical model to be fabricated in the very near future.

The effect of modulus on the performance of thermal conductive adhesives

By analyzing the effect of modulus of epoxy and modulus of filler particles on the thermal conductivity of thermal conductive adhesives (TCA), this paper concludes, in contrast to intuition, that the stiffer epoxy will generate a larger contact area, and the “soft” epoxy with modulus of 0.5GPa will create the largest contact area, hence the highest thermal conductivity. Therefore, it is advisable to adopt softer epoxy in TCA. On the other hand, this paper finds that if the shrinkage of epoxy is low, i.e. 1% linear shrinkage, fillers composed of a mixture of Ag flakes and certain high stiffness material will cause a higher thermal conductivity, i.e. 7% larger than that of pure Ag fillers. This suggests that with low shrinkage epoxy, it is advisable to mix Ag flakes with high stiffness particles, e.g. Diamond or SiC. However, when linear shrinkage of epoxy is high, i.e. 3%, the highest thermal conductivity is achieved by using pure Ag fillers. Therefore, in such cases it is not advisable to use Bi-model.

Molecular dynamics simulation of inertial trapping-induced atomic scale mass transport inside single walled carbon nanotubes

The forced transverse vibration of a single-walled carbon nanotube (SWNT) embedded with atomic-size particles was investigated using molecular dynamic simulations. The particles inside the cylindrical cantilever can be trapped near the antinodes or at the vicinity of the SWNT tip. The trapping phenomenon is highly sensitive to the external driving frequencies such that even very small changes in driving frequency can have a strong influence on the probability of the location of the particle inside the SWNT. The trapping effect could potentially be employed to realize the atomic scale control of particle position inside an SWNT via the finite adjustment of the external driving frequency. It may also be suggested that the trapping phenomenon could be utilized to develop high-sensitive mass detectors based on a SWNT resonator.

The Effect of Boundary Conditions on a Theoretical Analysis of Axial Buckling in a Chiral Single-Wall Carbon Nanotube

Using molecular dynamics simulation, we predict that under fixed-end boundary condition, for an unsymmetrical chiral single-wall carbon nanotubes (SWCNTs), helix-like stripes would appear on the nanotube shell, and torsional buckling could occur. At the same time, buckling critical strains would be greatly reduce (e.g., similar to 20% for a (8,3) SWCNT) compared with those under simply supported boundary conditions. The mechanism for this decrease is not understood.