Nanotube Curvature Research Articles

The adsorption of CO and NO on (8,0) SWCNT decorated with transition metals: A DFT study as a possible gas sensor

The adsorption and sensing capabilities of CO and NO on pristine and metal-decorated (8,0) SWCNT were analyzed by DFT. Both gases cause a slight deformation of the nanotube curvature in the direction of molecular adsorption. The molecule's adsorption and sensing performance are enhanced with the transition metal (Sc, Cr, Fe, and Ni) decoration on SWCNT. Decorated nanotubes are suitable for high-temperature sensors. According to relative energies for NO, the operational range is 900–1200 K. For CO/Cr- and Sc-SWCNT between 100 and 200 K and close to 550 K in the cases of decoration with Fe and Ni. From the recovery time analysis, the metal-decorated materials exhibit better performance at high temperatures and low pressures for NO compared to CO. Changes in magnetic moment suggest that Cr-decorated SWCNT could serve as a magnetic sensor for both molecules.

Percolation in Carbon Nanotube-Reinforced Polymers for Strain-Sensing Applications: Computational Investigation on Carbon Nanotube Distribution, Curvature, and Aggregation.

The present article investigates the possibility of simulating the electrical conductivity of carbon nanotube-reinforced polymer composites by numerical methods. Periodic representative volume elements are generated by randomly distributing perfectly conductive reinforcements in an insulating matrix and are used to assemble an electrical network representative of the nanocomposite, where the nanotube-nanotube contacts are considered equivalent resistors modeled by means of Simmons' equation. A comparison of the results with experimental data from the literature supports the conclusion that a random distribution of reinforcements is not suitable for simulating this class of materials since percolation thresholds and conductivity trends are different, with experimental percolation taking place before the expectations. Including nanotube curvature does not solve the issue, since it hinders percolation even further. In agreement with experimental observations, the investigation suggests that a suitable approach requires the inclusion of aggregation during the volume element generation to reduce the volume fraction required to reach percolation. Some solutions available in the literature to generate properly representative volume elements are thus listed. Concerning strain sensing, the results suggest that representative volume elements generated with random distributions overestimate the strain sensitivity of the actual composites.

Calibration of nonlocal generalized helical beam model for free vibration analysis of coiled carbon nanotubes via molecular dynamics simulations

This paper studied the free vibration behavior of coiled carbon nanotubes (CCNTs) using continuum mechanics methods and molecular dynamics (MD) simulations. Based on the continuum mechanics method, a new elasticity model called the nonlocal generalized Washizu beam (NGWB) was innovated by considering the effects of the curvature and cross-section thickness of nanotubes, as well as size-dependent effect. Then, the governing equations for the vibrational behavior of CCNTs were derived and solved using the numerical generalized differential quadrature method (GDQM). The free vibration behavior of CCNTs was also examined by performing the MD simulations to determine the calibrated values of the nonlocal parameter () that are applied in the NGWB elasticity model and to validate and evaluate the obtained results. Since the NGWB elasticity model considers the size-dependent effect on the vibrational behavior, obtained results from it well agrees with the MD simulation results in the present study. For CCNTs, there was a coupling between transverse, longitudinal, and torsional vibrations, which led to the beating phenomenon. The natural frequencies decreases by increasing the number of pitches ( aspect ratio and pitch angle The nonlocal parameter has a more significant effect on the frequencies of CCNTs with smaller geometrical parameters. In addition, the type of boundary conditions affects the calibrated values of the nonlocal parameter, frequency values, and arrangement of vibrating mode shapes of CCNTs. Results of the present study can be applied in the design and analysis of nano-electro-mechanical systems (NEMS), sensors, and nano-composite structures containing CCNTs. Also, the NGWB elasticity model might be useful in the statics and wave propagation studies of CCNTs, and other coiled and curved nano-structures.

Nonlinear Forced Vibration Analysis of Smart Curved CNTs Conveying Fluid

In this study, the nonlinear vibration of a curved carbon nanotube conveying fluid is analyzed. The nanotube is assumed to be covered by a piezoelectric layer and the Euler–Bernoulli beam theory is employed to establish the governing equations of motion. The influence of carbon nanotube curvature on structural modeling and fluid velocity vector is considered and the slip boundary conditions of CNT conveying fluid are included. The mathematical modeling of the structure is developed using Hamilton’s principle and then, the Galerkin procedure is employed to discretize the equation of motion. Furthermore, the frequency response of the system is extracted by applying the multiple scales method of perturbation. Finally, a comprehensive study is carried out on the primary resonance and piezoelectric-based parametric resonance of the system. It is shown that consideration of nanotube curvature may lead to an increase in nonlinearity. Implementing the fluid velocity vector in which nanotube curvature is included highly affects the maximum amplitude of the response and should not be ignored. Furthermore, different system parameters have evident impacts on the behavior of the system and therefore, selecting the reasonable geometrical and physical parameters of the system can be very useful to achieve a favorable response.

Co-assembled nanotubes with controlled curvature radius using a hydrogen bond regulation strategy.

The design of co-organized nanotube systems with controlled curvature radius that are realized by tilt modulation of co-assembled molecules, induced by the strength of non-covalent interactions in aqueous media, remains a significant challenge. Here, we report success in utilizing a hydrogen bond regulation strategy to stimulate molecular tilt for the formation of nanotubes with controlled curvature radius based on the co-assembly of two kinds of achiral cationic building blocks in aqueous solution. Computations and electron microscopy experiments suggest that the nanotube curvature radius drastically decreases as the tilt angle θ of co-assembled molecules increases with an increase of hydrogen bond strength. Interestingly, a slight change in the co-assembled molecular tilt causes a drastic change in the nanotube curvature radius.

A continuum study of ionic layer analysis for single species ion transport in coaxial carbon nanotubes

In this letter, we employ the Poisson-Nernst-Planck equation and the continuum molecular model to investigate the ionic layers formation in coaxial carbon nanotubes, which are crucial for understanding the ion transport in nanomaterials, as well as modern solar cells and batteries. Owing to the curvature of nanotubes and the strong ion-nanotubes interactions, our simulations show that stable ionic multi-layers can always be formed inside nanotubes under a wide range of external electric fields and operating temperatures. Approximate solutions have also been deduced to support our numerical results. Most importantly, our hybrid model enjoys rapid and efficient computational times and hence fluid flow, conductivity and VI curve can be extracted almost instantaneously, which opens up a new research direction for the ion transport in nanomaterials.

Frequency analysis of FG-CNT–reinforced composite doubly curved panels on visco-Pasternak medium

In this paper, the free damped vibration behavior of doubly curved panels is investigated, while reinforcements are aligned and straight single-walled carbon nanotubes with uniform and functionally graded distributions under four different patterns through thickness. The extended rule of mixtures is employed to achieve effective material properties. Hamilton principle and third-order shear deformation theory of Reddy are used for governing equations of motions of spherical, cylindrical, hyperboloid and paraboloid panels resting on visco-Pasternak medium. A semi-analytical approach with an iterative numerical algorithm is implemented to figure out frequencies and modal loss factors of eigenvalue problem. To verify, the present results are compared with those that are obtained via first-order shear deformation theory for flat, cylindrical, and spherical panels. Also, the influence of shallowness, thickness, curvature, aspect ratios, distribution and content of carbon nanotubes, and viscoelastic medium on natural frequency and damping capability of panels are examined via numerical examples. For the first time, the crossing phenomena of natural frequencies and modal loss factors of FG-CNT–reinforced composite panels with external damping under higher-order theory assumptions are presented. Results show that hyperboloid panels with high aspect, shallowness, and low thickness ratios are susceptible to follow inharmonic motion rather than a harmonic one.

Structural and electronic properties of defective AlN/GaN hybrid nanostructures

Due to the wide range of possible applications, atomically thin two-dimensional heterostructures have attracted much attention. In this work, using first-principles calculations, we investigated the structural and electronic properties of planar AlN/GaN hybrid heterojunctions with the presence of vacancies at their interfaces. Our results reveal that a single vacancy site, produced by the removal of Aluminum or Gallium atom, yields similar electronic band structures with localized states within the bandgap. We have also observed a robust magnetic behavior. A nitrogen-vacancy, on the other hand, induces the formation of midgap states with reduced overall magnetization. We have also studied nanotubes formed by rolling up these heterojunctions. The results showed that nanotube curvature does not substantially affect the electronic and magnetic properties of their corresponding planar AlN/GaN heterojunctions. For armchair-like nanotubes, a transition from direct to indirect bandgap was observed as a consequence of changing the system geometry from 2D to a quasi-one-dimensional one.

Imogolite in water: Simulating the effects of nanotube curvature on structure and dynamics

Imogolite is a fascinating inorganic nanotube that is found in nature or synthesized in a laboratory. The synthesis process is carried out in liquid media, and leads to the formation of almost monodisperse diameter nanotubes. Here we investigate, employing classical molecular dynamics simulations, the interaction of water and imogolite for nanotubes of several radii. We established that water penetrates the pores of N = 9 and larger nanotubes, and adopts a coaxial arrangement in it. Also, while water molecules can diffuse along the center of the nanotube, the molecules next to the inner imogolite walls have very low mobility. At the outer nanotube wall, an increase of water density is observed, this effect extends up to 1 nm, beyond which water properties are bulk-like. Both phenomena are affected by the imogolite curvature.

Curvature-dependent melting models and melting thermodynamics of nanotubes in theory and experiment

Currently, the melting thermodynamic properties of nanotubes are still unclear. In this paper, the generalized relation of chemical potential of nano-condensed phases was first derived, and two types of curvature surfaces with different phase transition activities were found on nanotubes. On this basis, two melting models of nanotubes were proposed, the relations between the melting temperature, the melting thermodynamic properties, respectively, and the curvature (reciprocal of the radius) of nanotubes were derived. And the correctness of the theory was verified by the melting of selenium nanotube. The results showed that the initial melting temperature, melting enthalpy and melting entropy decrease with increasing the curvature, and present good linear relationships with curvature, respectively. This theory can provide theoretical guidance and new clues for the design, preparation, research and applications of nanomaterials with negative curvature surface.

Tuning the structure of monomeric amyloid beta peptide by the curvature of carbon nanotubes

Carbon nanotubes can affect the self-assembly of amyloid beta peptides (Aβ) related to neurodegenerative diseases. We use molecular dynamics (MD) to investigate the effects of carbon nanotubes (CNT) on the conformational evolution of monomeric Aβ1-42 peptide. The chirality of CNT varies from (10, 10), (15, 15), (20, 20) and (25, 25) that corresponds to declining curvatures. We show that the adhesion of peptide on CNT surface leads to internal structures predisposes to collapse, which might be reasonable methods to impede the initial nucleation and self-assembly. Adsorption induce the loss of the peptides' native structures. Adsorption and subsequent denaturation accompanies by a loss of surface hydration of peptide. When the curvature of CNT decreases, peptide spread almost completely over the CNT surface. Conversely, peptide will wrap around the CNT when the curvature of CNT is high. Peptide adsorption onto CNT also reduces their α-helical content and β-sheet ratio, indicating that the CNT significantly affect the formation of α-helical structures while inducing random coil conformations. The arrangement of peptides on CNT surface relates to the affinity of various amino acids onto CNT. These insights provide useful information for understanding the binding and winding tendency of peptides on carbon nanostructures’ surface.

Enhancing hydrogen evolution activity by doping and tuning the curvature of manganese-embedded carbon nanotubes

Doping heteroatoms (Mn and N) and tuning the curvature of carbon nanotubes could efficiently elevate the C p-band center, lower the absolute electrode potential, and thus enhance the HER performance.

A closed-form model for estimating the effective thermal conductivities of carbon nanotube–polymer nanocomposites

This paper describes a closed-form unit cell micromechanical model for estimating the effective thermal conductivities of unidirectional carbon nanotube reinforced polymer nanocomposites. The model incorporates the typically observed misalignment and curvature of carbon nanotubes into the polymer nanocomposites. Also, the interfacial thermal resistance between the carbon nanotube and the polymer matrix is considered in the nanocomposite simulation. The micromechanics model is seen to produce reasonable agreement with available experimental data for the effective thermal conductivities of polymer nanocomposites reinforced with different carbon nanotube volume fractions. The results indicate that the thermal conductivities are strongly dependent on the waviness wherein, even a slight change in the carbon nanotube curvature can induce a prominent change in the polymer nanocomposite thermal conducting behavior. In general, the carbon nanotube curvature improves the nanocomposite thermal conductivity in the transverse direction. However, using the straight carbon nanotubes leads to maximum levels of axial thermal conductivities. With the increase in carbon nanotube diameter, an enhancement in nanocomposite transverse thermal conductivity is observed. Also, the results of micromechanical simulation show that it is necessary to form a perfectly bonded interface if the full potential of carbon nanotube reinforcement is to be realized.

Effects of curvature and alignment of carbon nanotubes on the electrical conductivity of carbon nanotube-reinforced polymers investigated by mesoscopic simulations

Carbon nanotube-reinforced polymers belong to a class of composite materials, which have been largely investigated due to their special electrical, thermal and mechanical properties. In the case of electrical conductivity of carbon nanotube-reinforced polymer, a critical amount of carbon nanotubes as a filler material enables a sharp increase of electrical conductivity. At this certain volume fraction of carbon nanotubes, the material turns into a conductor because of the percolation effect. This effect occurs due to the formation of a closed pathway of filler material through the system. Mesoscopic simulation models of these materials were carried out to predict their electrical conductivity. In this paper, the effects of carbon nanotube curvature and their alignment parallel or perpendicular to the electrical flow direction inside a representative volume element were analysed and an optimized carbon nanotube distribution is presented. A network with a longest average path length per (rigid) carbon nanotube but also cross-linking (only nearly isotropic alignment) shows the best conductivity in the preferred direction.

Characterizing the sensitivity of bonds to the curvature of carbon nanotubes.

The way the bonding and reactivity of armchair carbon nanotubes depends on the curvature of the nanotube has been investigated using density functional theory. To understand the nature of the interaction between atoms in the nanotube, the Wiberg bond index, natural bond order analysis, and topological electron density analysis have been performed. All these tools confirm that the bonds in the hydrogen-capped carbon nanotubes considered here are primarily covalent. As the diameter of the nanotube decreases and its curvature increases, the covalency (bond order) decreases, a conclusion that is supported by the increase of the bond lengths and also the decrease of the electron density and the energy density along the bond paths as the curvature increases. To shed light on the orbital contribution in bond formation and the most effective interaction between donor bonding orbital and acceptor antibonding orbital, analysis of natural bond orbitals is carried out. We have observed that the higher the nanotube diameter is, the higher the energy gap.

Unveiling Adsorption Mechanisms of Organic Pollutants onto Carbon Nanomaterials by Density Functional Theory Computations and Linear Free Energy Relationship Modeling.

Predicting adsorption of organic pollutants onto carbon nanomaterials (CNMs) and understanding the adsorption mechanisms are of great importance to assess the environmental behavior and ecological risks of organic pollutants and CNMs. By means of density functional theory (DFT) computations, we investigated the adsorption of 38 organic molecules (aliphatic hydrocarbons, benzene and its derivatives, and polycyclic aromatic hydrocarbons) onto pristine graphene in both gaseous and aqueous phases. Polyparameter linear free energy relationships (pp-LFERs) were developed, which can be employed to predict adsorption energies of aliphatic and aromatic hydrocarbons on graphene. Based on the pp-LFERs, contributions of different interactions to the overall adsorption were estimated. As suggested by the pp-LFERs, the gaseous adsorption energies are mainly governed by dispersion and electrostatic interactions, while the aqueous adsorption energies are mainly determined by dispersion and hydrophobic interactions. It was also revealed that curvature of single-walled carbon nanotubes (SWNTs) exhibits more significant effects than the electronic properties (metallic or semiconducting) on gaseous adsorption energies, and graphene has stronger adsorption abilities than SWNTs. The developed models may pave a promising way for predicting adsorption of environmental chemicals onto CNMs with in silico techniques.

TDDFT-Based Spin–Orbit Couplings of 0D, 1D, and 2D Carbon Nanostructures: Static and Dynamical Effects

Carbon nanostructures (CNS) constitute an important class of materials derived from graphene that share remarkable photophysical and photochemical properties of potential interest for a number of technological applications, ranging from electron transport and spintronics to heat conduction and solar energy conversion. In this work, we use linear-response time-dependent density functional theory (LR-TDDFT) for the calculation of spin–orbit couplings (SOC) and intersystem crossing transitions in a number of CNS including: 0D quantum dots (C60 and graphene nanoflakes), 1D carbon nanotubes, and 2D graphene. The method developed in [J. Chem. Phys. 2014, 140, 144103] and [J. Chem. Phys. 2015, 143, 224105] is able to capture the dependence of the SOC values on subtle electronic structure differences characterizing the different 0D, 1D, and 2D CNS and on geometrical properties such as curvature and topological indices of carbon nanotubes. Compared to tight-binding calculations, our first-principles approach is able to reproduce very accurate results without the need of any ad-hoc parametrization. When combined with nonadiabatic dynamics, SOC can be used to compute intersystem crossing transitions between states of different spin multiplicities, opening new avenues in the study of the complex dynamics of photoexcited CNS. In particular, we analyze the dependence of the intersystem crossing rates on thermal structural fluctuations in a carbon nanoflake.

How the alignment of adsorbed ortho H pairs determines the onset of selective carbon nanotube etching.

Unlocking the enormous technological potential of carbon nanotubes strongly depends on our ability to specifically produce metallic or semiconducting tubes. While selective etching of both has already been demonstrated, the underlying reasons, however, remain elusive as yet. We here present computational and experimental evidence on the operative mechanisms at the atomic scale. We demonstrate that during the adsorption of H atoms and their coalescence, the adsorbed ortho hydrogen pairs on single-walled carbon nanotubes induce higher shear stresses than axial stresses, leading to the elongation of HC-CH bonds as a function of their alignment with the tube chirality vector, which we denote as the γ-angle. As a result, the C-C cleavage occurs more rapidly in nanotubes containing ortho H-pairs with a small γ-angle. This phenomenon can explain the selective etching of small-diameter semiconductor nanotubes with a similar curvature. Both theoretical and experimental results strongly indicate the important role of the γ-angle in the selective etching mechanisms of carbon nanotubes, in addition to the nanotube curvature and metallicity effects and lead us to clearly understand the onset of selective synthesis/removal of CNT-based materials.

Understanding thermal conductance across multi-wall carbon nanotube contacts: Role of nanotube curvature

Thermal energy transfer at the interconnects in carbon based nanoelectronic devices plays a crucial role towards their performance as well as their reliability. In this study, we investigate such thermal energy transfer across physically interacting multi-wall carbon nanotubes (MWCNTs) as a function of their diameter, length, number of walls, inter-layer chirality differences, and different angular orientation of the cross-contact. Using non-equilibrium molecular dynamics simulations for phonon energy transfer, we predict that MWCNTs' curvature and their number of walls emerge as two critical factors, with each of them determining the limiting value of the thermal conductance across MWCNT contacts in different diameter regimes. For thinner MWCNTs, the curvature determines the limiting value of the conductance and leads to an interesting non-monotonic character, while the number of walls dominates the contact conductance for large diameter MWCNTs. We discuss their respective origins and distinguish their governing regimes using several arguments –focusing of phonons, and confinement of the phonon focusing cone, large mean free path of graphite– and how they modulate radial thermal transport, leading to observed trends of thermal conductance across MWCNT contacts.

Influence of the surface curvature of carbon nanotubes on their conductivity in the dirac approximation

A method of surface curvature of carbon nanotubes has been proposed for quantitative estimation of the longitudinal conductivity of nanotubes. A dispersion relation for the electron spectrum of single-walled carbon nanotubes has been obtained analytically. The change in the zone structure of nanotubes of various types and diameters caused by taking into account the surface curvature has been analyzed. The temperature dependence of the longitudinal component of conductivity with allowance for the surface curvature for a series of nanotubes has been calculated. The comparison with the conductivity of a plane graphene has been performed. It has been shown that, in zig-zag tubes, the correction of the conductivity for the surface curvature decreases with an increase in temperature as well as with an increase in the radius of curvature.