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Many recently synthesized materials feature aligned arrays or bundles of carbon nanotubes (CNTs) whose mechanical properties are partially determined by the van der Waals interactions between adjacent tubes. Of particular interest in this paper are instances where the resulting interaction between a pair of CNTs often produces a forklike structure. The mechanical properties of this structure are noticeably different from those for isolated individual CNTs. In particular, while one anticipates buckling phenomena in the forked structure, an adhesion instability may also be present. New criteria for buckling and adhesion instabilities in forklike structures are presented in this paper. The criteria are illuminated with a bifurcation analyses of the response of the forklike structure to applied compressive and shear loadings.

The paper at hand investigates degradation of elastic properties of a composite material reinforced by carbon nanotubes. Sources of degradation are waviness of a nanotube, vacancies and 5-7-7-5 defects. The manuscript aims to establish the computational procedure based on the atomistic finite element method for estimation of elastic properties by accounting for these defects. An epoxy nanocomposite with typical properties is selected and carefully analysed. Special attention is devoted to proper simulation of van der Waals forces at the matrix-nanotube interface. A series of numerical experiments with different waviness ratios and type of defects is performed and based on these results interpolation of elastic properties is carried out. It is found that proper modelling of van der Waals interactions and waviness has a profound influence on the mechanical behaviour of the nanocomposite, while the other type of defects are of secondary importance.

The elastic properties of a carbon nanotube (CNT) reinforced composite are affected by many factors such as the CNT–matrix interphase. As such, mechanical analysis without sufficient consideration of these factors can give rise to incorrect predictions. Using single-walled carbon nanotube (SWCNT) reinforced Polyvinylchloride (PVC) as an example, this paper presents a new technique to characterize interphase regions. The representative volume element (RVE) of the SWCNT–PVC system is modeled as an assemblage of three phases, the equivalent solid fiber (ESF) mimicking the SWCNT under the van der Waals (vdW) forces, the dense interphase PVC of appropriate thickness and density, and the bulk PVC matrix. Two methods are proposed to extract the elastic properties of the ESF from the atomistic RVE and the CNT-cluster. Using atomistic simulations, the thickness and the average density of interphase matrix are determined and the elastic properties of amorphous interphase matrix are characterized as a function of density. The method is examined in a continuum-based three-phase model developed with the aid of molecular mechanics (MM) and the finite element (FE) method. The predictions of the continuum-based model show a good agreement with the atomistic results verifies that the interphase properties of amorphous matrix in CNT-composites could be approximated as a function of density. The results show that ignoring either the vdW interaction region or the interphase matrix layer can bring about misleading results, and that the effect of internal walls of multi-walled carbon nanotubes (MWCNTs) on the density and thickness of the dense interphase is negligible.

A hybrid nanowire (HNW) was constructed by coating a single-wall carbon nanotube (SWCNT) with piezoelectric zinc oxide (ZnO). The two components of the HNW interact with each other via the van der Waals (vdW) force. This paper aims to study the effect of the piezoelectricity in the ZnO layer and the inter-phase vdW interaction on the fundamental vibration of the HNWs. In doing this, a new model was developed where the two components of the HNWs were modeled as Euler beams coupled via the interphase vdW interaction. Based on the model, the dependence of the frequency on an applied electrical voltage was calculated for HNWs of different geometric sizes to reveal the voltage effect. The results were then compared with those calculated without considering the inter-phase vdW interaction. It was found that the interphase vdW interaction can substantially decrease the structural stiffness, leading to a greatly enhanced piezoelectric effect but a lower frequency for the vibration of the HNWs.

A new inverse approach is proposed in this paper, which combines elements of nonlocal theory and molecular mechanics, based on the experimental results available in the nanoindentation literature. The effect of the inlayer van der Waals atomistic interactions for carbon nanotubes with multiple walls (MWCNT) is included by means of the Brenner-Tersoff potential and experimental results. The neighboring walls of MWCNT are coupled through van der Waals interactions, and the shell buckling would initiate in the outermost shell, when nanotubes are short. The nanoindentation technique is simulated for the axially compressed of individual nanotubes, in order to evaluate the load-unloaded-displacement, the curve critical buckling and the appropriate values for local Lamé constants.

At the nanoscale a number of very high frequency oscillating systems involving relative motion with respect to a carbon nanotube have been identified. In this paper, we study the two-body systems of an atom and a fullerene C60 orbiting around a single infinitely long carbon nanotube and a fullerene C60 orbiting around a fullerene C1500. The van der Waals interaction forces are modeled using the Lennard–Jones potential together with the continuum approach for which carbon atoms are assumed to be uniformly distributed over the surfaces of both the fullerenes and the carbon nanotube. Some analytical and perturbation solutions are obtained for the regime where the attractive term of the potential energy dominates. Certain circular orbiting radii of these nanoscale systems are estimated using a stability argument and the corresponding circular orbiting frequencies can then be calculated by investigating the minimum energy configuration of their effective potential energies. We find that the circular orbiting frequencies of the various proposed nano-systems are in the gigahertz range. Finally, the classification of their orbiting paths is determined numerically.

Aromatic hydrocarbon molecules encapsulated in carbon nanotubes have been proposed for applications as semiconductors. They can be formed by exploiting the van der Waals interaction as a simple method to incorporate molecules into carbon nanotubes. However, the existence of energy barriers near the open ends of carbon nanotubes may be an obstacle for molecules entering carbon nanotubes. In this paper, we investigate the encapsulation mechanism of a typical aromatic hydrocarbon, namely a benzene molecule, into a carbon nanotube in order to determine the dependence on radius of the tube. A continuous approach which assumes that the molecular interactions can be approximated using average atomic densities together with the semi-empirical Lennard-Jones potential function is adopted, and an analytical expression for the interaction energy is obtained which may be readily evaluated by algebraic computer packages. In particular, we determine the threshold radius of the carbon nanotube for which the benzene molecule will enter the carbon nanotube. The analytical approach adopted here provides a computationally rapid procedure for the determination of critical numerical values. Refereed/Peer-reviewed

Single-walled carbon nanotubes (SWNTs) possess extraordinary electrical properties, with many possible applications in electronics. Dense, horizontally aligned arrays of linearly configured SWNTs represent perhaps the most attractive and scalable way to implement this class of nanomaterial in practical systems. Recent work shows that templated growth of tubes on certain crystalline substrates yields arrays with the necessary levels of perfection, as demonstrated by the formation of devices and full systems on quartz. This paper examines advanced implementations of this process on crystalline quartz substrates with different orientations, to yield strategies for forming diverse, but well-defined horizontal configurations of SWNTs. Combined experimental and theoretical studies indicate that angle-dependent van der Waals interactions can account for nearly all aspects of alignment on quartz with X, Y, Z, and ST cuts, as well as quartz with disordered surface layers. These findings provide important insights into methods for guided growth of SWNTs, and possibly other classes of nanomaterials, for applications in electronics, sensing, photodetection, light emission, and other areas.

The present paper examines the thermal effect on axially compressed buckling of a multiwalled carbon nanotube based on the gradient elasticity theories. The small-size effect, which plays an essential role in the buckling behavior with large aspect ratios under axial compression coupling with temperature change, is captured by applying different gradient elasticity theories including stress and strain. In this model, each of the nested concentric tubes is regarded as an individual column and the deflection of all the columns is coupled together through the van der Waals interactions between adjacent tubes.