Design of High-Frequency Carbon Nanotube-Carbon Nanotorus Oscillators for Energy Harvesting: A Molecular Dynamics Study

The objective of this study is to examine the feasibility of using carbon-based nanostructures as nano-oscillators for future nanoelectromechanical applications such as energy harvesting devices and vibration sensing. The proposed nano-oscillator is comprised of a carbon nanotube (CNT) oscillating through a fixed carbon nanotorus molecule. For the first time in the literature, molecular dynamics (MD) simulations in conjunction with the Tersoff-Brenner (TB) and 6-12 Lennard-Jones (LJ) potential functions are adopted to determine the molecular interactions of the introduced nanodevice. To simulate the oscillatory behavior, two different schemes, namely, rigid and flexible, are considered. A detailed parametric study is performed to investigate the effects of rigidity, flexibility, and size of nanostructures as well as initial velocity on the force distribution and time histories of displacement and velocity of the core. Numerical results reveal that unlike the rigid oscillators, the flexible oscillators damp out within a few cycles. It is shown that the escape velocity of the flexible scheme is ∼6 times greater than that of the rigid scheme. The operating frequency and the generated power of rigid and flexible schemes under different system parameters are also calculated and compared. It is demonstrated that with increasing the ratio of nanotube-to-nanotorus diameter, the operating frequencies of both schemes decrease, while the generated powers do not behave monotonically. For a determined system parameter, it is observed that the flexible scheme provides higher operating frequencies compared to the rigid one. Moreover, considering that the initial velocity of the system is identical to the escape velocity, the generated power of the flexible scheme is calculated to be ∼14 times greater than that of the rigid scheme.

High velocity impact analysis of free-free carbon nanotubes

In the present work, molecular dynamics (MD) simulations are used to investigate the impact behavior of single-walled carbon nanotubes (SWCNTs) with free boundary conditions in two directions, i.e. vertical and horizontal. To consider the effect of consecutive impacts, the number of carbon nanotubes (CNTs) participated in simulations is chosen from two to five in a row. MD results show that adding the number of impacts increases the magnitude of energy loss in both mentioned directions and reduces the maximum impact force in horizontal cases. In addition, by increasing the velocity of striker CNT from 1 km/s to the maximum value which causes any fracture, the effect of initial velocity on the impact properties and also the ultimate initial velocity for each model are investigated. It is demonstrated that the energy loss and the maximum value of impact force increase as the initial velocity of the striker increases. Also, it is found that the impact strength in the vertical direction is higher than that of the horizontal one, while the horizontal CNTs perform better in the absorption of impact energy. Moreover, for all models, the fracture mechanism of CNTs resulting from the impact process is represented and the procedure of failure is explained.

Fundamental frequency analysis of endohedrally functionalized carbon nanotubes with metallic nanowires: a molecular dynamics study

The endohedral functionalization of carbon nanotubes (CNTs) with nanowires (NWs), i.e., NWs@CNTs, has been the center of attention in a lot of research due to the applications of NWs@CNTs in nanoelectronic devices, heterogeneous catalysis, and electromagnetic wave absorption. To this end, based on the classical molecular dynamics (MD) simulations, the effect of four pentagonal structures of encapsulated metallic nanowires (mNWs), namely the eclipsed pentagon (E), the deformed staggered pentagon (Ds), staggered pentagon (S), and staggered pentagonal structure without the monatomic chain passing through the centers of the parallel pentagons (R) configurations on the vibrational behavior of CNTs, is investigated. Also, the effects of geometrical parameters such as length and radius of CNTs on the natural frequencies of simulated models are explored. The results illustrate that by increasing the length, the natural frequency of pure CNTs and mNWs@CNTs decreases. In a similar length, mNWs@CNTs possess lower natural frequencies compared to the pure CNTs. According to the results, the highest and lowest natural frequencies are calculated by inserting the S structure of sodium NW and Ds structure of aluminum NW inside their proper armchair CNT, i.e., Na-S NW@ (9,9) CNT and Al-Ds NW@ (7,7) CNT, respectively.

A molecular dynamics study on the buckling behavior of single-walled carbon nanotubes filled with gold nanowires

Molecular dynamics (MD) simulations are carried out to study the buckling of pure gold nanowires (GNWs) and hybrid GNWs@single-walled carbon nanotubes (SWCNTs). The effects of geometrical parameters and endohedral filling of SWCNTs on the critical buckling force are taken into consideration. Two different types of GNWs, namely multi-shell and pentagonal GNWs, with various structures are considered. The results illustrate that the buckling force of the pure GNWs is less than those of the pure SWCNTs and hybrid structures. Also, GNWs possess higher buckling forces by increasing their cross-section area. It is observed that enclosing the GNWs by SWCNTs improves the mechanical behaviors of both CNTs and GNWs. In hybrid multi-shell GNWs@SWCNTs, by increasing the radius, the effect of encapsulation on the buckling force is more remarkable. It can be seen that the encapsulation of pentagonal GNWs has a slightly more effect on the buckling behavior than the encapsulation of multi-shell GNWs. Moreover, it is found out that by increasing the length, the buckling force decreases.

Tensile characteristics of carbene-functionalized CNTs subjected to physisorption of polymer chains: a molecular dynamics study

Tensile properties such as Young's modulus and ultimate tensile force are important properties in understanding the characteristics of nanocomposites. Besides, the importance of functionalization methods in modification of the unique mechanical and elastic properties of carbon nanotubes (CNTs) is being widely recognized. In this paper, the tensile properties of CNTs functionalized with carbene under physisorption of polymer chains, i.e., aramid and polyketone chains, are investigated by using a series of molecular dynamics (MD) simulations. The results illustrated that Young's modulus of carbene-functionalized CNTs (cfCNTs) decreases by rising the weight percentage of carbene. By contrast, Young's modulus of cfCNTs under physisorption of polymer chains (cfCNTs/polymers) increases as the carbene weight rises. In a particular carbene weight, Young's modulus of cfCNTs/polymers decreases by increasing the chains of non-covalent functional groups. Moreover, it is shown that similar to Young's modulus, ultimate tensile force of cfCNTs reduces by increasing the weight percentage of carbene whereas the ultimate tensile force of cfCNTs/polymers has an increasing trend with raising the carbene weight.

Interfacial properties of 3D metallic carbon nanostructures (T6 and T14)-reinforced polymer nanocomposites: A molecular dynamics study

Herein, the interfacial properties of new three-dimensional (3D) configurations of metallic carbon, namely T6 and T14, incorporated to different polymer matrices (T6 and T14@polymers) are studied using molecular dynamics (MD) simulations. The effects of two types of shape models for T6 and T14, i.e. beam- and plate-like models, various square cross-sectional areas for the reinforcements, pull-out velocity and polymer structure on the interaction energy and pull-out force of final system are investigated. The results reveal that the interfacial resistance of the system is improved by imposing a high pull-out velocity to the nanofillers. For each pull-out velocity, the effect of beam-like T6 and T14@polycarbonate (beam-like T6 and T14@PC) on increasing average pull-out force is more remarkable than that of similar models surrounded by polypropylene (PP). The beam- and plate-like structures@polymers possess the lowest and highest interfacial resistance, respectively. As the aspect ratio (length-to-width ratio) of nanofillers changes from the lowest value to the highest one, the average pull-out force decreases. The average pull-out force of plate-like T6@polymers is higher than their plate-like T14 counterparts. Besides, higher absolute values of interaction energy in plate-like T6 and T14@polymers in comparison with others imply that the load-carrying capacity from the surrounding matrix to the plate-like nanofillers is significantly increased.

On the mechanical stability and buckling analysis of carbon nanotubes filled with ice nanotubes in the aqueous environment: A molecular dynamics simulation approach

In this article, molecular dynamics (MD) simulations are utilized to investigate the buckling behavior of carbon nanotubes (CNTs) containing ice nanotubes in the vacuum and aqueous environment. The obtained results show that unlike the critical strain, the critical buckling load of CNT containing ice nanotube is higher than that of pure CNT in the vacuum. It is also indicated that the sensitivity of critical buckling load and the critical strain of CNT containing ice nanotube to the variation of length decreases when the nanostructure is subjected to the aqueous environment. Additionally, it is observed that the calculated critical buckling load and the critical strain of CNTs filled with ice nanotubes in the aqueous environment are respectively larger and smaller than those obtained in the vacuum. It is further observed that CNTs lose their symmetric buckling mode shape as they are filled with ice nanotubes in the vacuum. The results of these simulations can be used as a benchmark for further studies in designing novel potential applications such as proton electronic-based nanoelectromechanical systems (NEMS).

Buckling analysis of defective cross-linked functionalized single- and double-walled carbon nanotubes with polyethylene chains using molecular dynamics simulations

Functionalized carbon nanotubes (CNTs) can be used for improving the mechanical properties and load transfer in nanocomposites. In this research, the buckling behavior of perfect and defective cross-linked functionalized CNTs with polyethylene (PE) chains is studied employing molecular dynamics (MD) simulations. Two different configurations with the consideration of vacancy defects, namely mapped and wrapped, are selected. According to the results, critical buckling force of cross-linked functionalized CNTs with PE chains increases as compared to pure CNTs, especially in the case of double-walled carbon nanotubes (DWCNTs). By contrast, it is demonstrated that critical strain of cross-linked functionalized CNTs decreases as compared to that of pristine CNTs. Also, it is observed that increasing the weight percentage leads to the higher increase and the decrease in critical buckling force and strain of cross-linked functionalized CNTs, respectively. Moreover, the presence of defect considerably reduces both critical buckling force and strain of cross-linked functionalized CNTs. Finally, it is shown that the critical buckling strain is more sensitive to the presence of defects as compared to critical buckling force.

Characterization of the Mechanical Properties of Monolayer Molybdenum Disulfide Nanosheets Using First Principles

Recently, synthesized inorganic two-dimensional monolayer nanostructures are very promising to be applied in electronic devices. This article explores the mechanical properties of a monolayer molybdenum disulfide (MoS2) including Young's bulk and shear moduli and Poisson's ratio by applying density functional theory (DFT) calculation based on the generalized gradient approximation (GGA). The results demonstrate that the elastic properties of MoS2 nanosheets are less than those of graphene and hexagonal boron-nitride (h-BN) nanosheets. However, their Poisson's ratio is found to be higher than that of graphene and h-BN nanosheet. It is also observed that due to the special structure of MoS2, the thickness of nanosheet changes when the axial strain is applied.