Straight Carbon Nanotubes Research Articles

In vitro and in vivo genotoxic effects of straight versus tangled multi-walled carbon nanotubes

Some multi-walled carbon nanotubes (MWCNTs) induce mesothelioma in rodents, straight MWCNTs showing a more pronounced effect than tangled MWCNTs. As primary and secondary genotoxicity may play a role in MWCNT carcinogenesis, we used a battery of assays for DNA damage and micronuclei to compare the genotoxicity of straight (MWCNT-S) and tangled MWCNTs (MWCNT-T) in vitro (primary genotoxicity) and in vivo (primary or secondary genotoxicity). C57Bl/6 mice showed a dose-dependent increase in DNA strand breaks, as measured by the comet assay, in lung cells 24 h after a single pharyngeal aspiration of MWCNT-S (1–200 μg/mouse). An increase was also observed for DNA strand breaks in lung and bronchoalveolar lavage (BAL) cells and for micronucleated alveolar type II cells in mice exposed to aerosolized MWCNT-S (8.2–10.8 mg/m3) for 4 d, 4 h/d. No systemic genotoxic effects, assessed by the γ-H2AX assay in blood mononuclear leukocytes or by micronucleated polychromatic erythrocytes (MNPCEs) in bone marrow or blood, were observed for MWCNT-S by either exposure technique. MWCNT-T showed a dose-related decrease in DNA damage in BAL and lung cells of mice after a single pharyngeal aspiration (1–200 μg/mouse) and in MNPCEs after inhalation exposure (17.5 mg/m3). In vitro in human bronchial epithelial BEAS-2B cells, MWCNT-S induced DNA strand breaks at low doses (5 and 10 μg/cm2), while MWCNT-T increased strand breakage only at 200 μg/cm2. Neither of the MWCNTs was able to induce micronuclei in vitro. Our findings suggest that both primary and secondary mechanisms may be involved in the genotoxicity of straight MWCNTs.

MONTE CARLO STUDIES OF ELECTRONIC TRANSPORT IN HELICALLY COILED CARBON NANOTUBES

We studied the stationary electron transport of semiconduction single-wall straight and helically coiled carbon nanotubes in the presence of electron- phonon interaction. The electron and phonon bands as well as electron phonon coupling matrix elements are obtained from quantum mechanical calculations with the application of symmetry. Total scattering rate for all electronic states relevant for charge transport is obtained as a sum over independent processes. Transport simulation is realized by Monte Carlo algorithm, where free flight time and scattering mechanism are selected randomly. The obtained electron transport properties of helically coiled and straight carbon nanotubes are significantly different. The electron drift velocities in helically coiled nanotubes are several times lower than in straight carbon nanotubes.

Optical effect on the growth of Ni-filled carbon nanotubes using gas/solid interfacial discharge pyrolysis

We report on a growth technique of carbon nanotubes (CNTs) whose core and interlayer spaces were filled with Ni fine particles using discharge pyrolysis at gas/solid interface with optical-parametric-oscillation (OPO) laser beam assist. Transmission electron microscope observation reveals that CNTs were grown at around a cathode spot and, in most cases, Ni fine particles had 3–4 nm diameters. With decreasing the wavelength of OPO laser, G/D ratios obtained from Raman spectrum analysis increased gradually and, in fact, the structures of CNTs were improved from amorphous-like structures to the long and straight CNTs. For longer wavelengths (593 nm, 650 nm) of OPO laser, diameters of CNTs became thicker (typically 10 ~ 100 nm) and therefore, Ni nanowires were formed in the core spaces of CNTs. However, for shorter wavelength (456 nm, 507 nm), diameters of CNTs were significantly reduced and Ni fine particles were embedded in between CNT layers. It was found that the structures of CNTs strongly depend on both...

Simulation of methane adsorption and diffusion in a carbon nanotube channel

The effect of pore-connectivity feature of nanoporous carbons (NPCs) on the adsorptive and diffusive behavior of methane was studied by a simple constricted carbon nanotube (C-CNT) model using grand canonical Monte Carlo and molecular dynamics simulations. In spite of slight overprediction, C-CNT model can properly predict the adsorption of methane in some real NPCs. The calculated heat of adsorption was well agreed with the reported values for the hypothetical Schwarzite (C168) model and activated carbon. The obtained results show that the most preferred site for the adsorption of methane is the constricted region of the pore. The effect of constriction length on the methane uptake was studied at various pressures. It was shown that at low pressures the methane uptake increased with the length of constriction, while at high pressures the uptake is larger for short constriction. The diffusion coefficients of methane inside the C-CNT were calculated by very long MD simulations (220ns). The calculated methane diffusion coefficients in the C-CNT were one to two orders of magnitude lower than that in the regular slit pores as well as the straight carbon nanotubes. In addition, the diffusion coefficients in the C-CNT were in the same order of magnitude as in the constricted slit and virtual porous carbon (VPC) models of carbon pores. MD simulations revealed that the diffusivity decreases with the constriction length and approaches a constant value for large constriction length.

Carbon nanomaterials synthesized using a spray pyrolysis method

Carbon nanomaterials were synthesized using a spray pyrolysis chemical vapor deposition system (SPCVD). By varying the reaction temperature or flow rate of the carbon source, the structure or morphology of the synthesized carbon nanocoils (CNCs) can be controlled. A vertical chemical vapor deposition (CVD) furnace with a three-stage heating zone was employed to synthesize carbonaceous nanomaterials using nano-Pd catalysts at growth temperatures of 600, 700, and 800 °C. The morphology of the synthesized carbon products and the relationship between the carbon source concentration and its yield were evaluated. The results showed that CNCs formed at a lower temperature (600 °C), whereas straight carbon nanotubes were obtained at a higher temperature (700 or 800 °C). The structure and morphology of the carbonaceous samples were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Their graphite crystallinity was analyzed using Raman spectroscopy. When the three heating zones of the vertical CVD chamber were set to different temperatures, a unique nano-carbonaceous material with a special morphology similar to an octopus tentacle was formed.

On the tensile behavior of hetero-junction carbon nanotubes

Several straight hetero-junctions carbon nanotubes (CNTs) are constructed and their tensile behavior are investigated. It is pointed that the Young's modulus of hetero-junctions is lower than the values of their fundamental homogeneous CNTs due to the existence of pentagon–heptagon pair defects. In addition, it is revealed that the Young's modulus of homogeneous zigzag CNTs increases by increasing the chiral number of these nano-structures. Finally, it is concluded that as the connecting length of the hetero-junctions increases the Young's modulus of these particular CNTs decreases. Therefore, the tensile strength of hetero-junctions depends on the presence of pentagon–heptagon pair defects.

Theoretical study of energy band splitting induced by spin–orbit interaction in helically coiled carbon nanotubes

Abstract Recent theoretical and experimental works on straight carbon nanotubes (SCNTs) have revealed that the curvature could enhance the spin–orbit interaction (SOI). Motivated by this, we further explore the effective SOI with another different curvature in helically coiled carbon nanotubes (HCCNTs) using the tight-binding model and perturbation approach. Finally, we derive the effective SOI in HCCNTs, and find the electron–hole asymmetric spin splitting. Interestingly, the asymmetric splitting largely depends on coil pitch p and coil radius r, which are not known in SCNTs. These results should be valuable for spintronic applications of carbon nanotubes.

Nonstraight nanochannels transfer water faster than straight nanochannels.

Understanding the flow of liquids and particularly water in nanochannels is important for scientific and technological applications, such as for filtration and drug delivery. Here we perform molecular dynamics simulations to investigate the transfer of single-file water molecules across straight or nonstraight single-walled carbon nanotubes (SWCNTs). In contrast with the macroscopic scenario, the nonstraight nanostructure can increase the water permeation. Remarkably, compared with the straight SWCNT, the nonstraight SWCNT with the minimal bending angle of 35° in the simulations can enhance the water transport up to 3.5 times. This enhancement mainly originates from the Lennard-Jones interaction between water molecules and nonstraight nanostructures. Our work offers an additional freedom to design high-flux nanochannels by choosing nonstraight nanostructures and provides an insight into water flow across biological water nanochannels, which are often nonstraight since they are composed of integral membrane proteins.

Nonlinear forced vibration response of smart two-phase nano-composite beams to external harmonic excitations

Abstract This paper presents an analytical solution for nonlinear free and forced vibration response of smart laminated nano-composite beams resting on nonlinear elastic foundation and under external harmonic excitation. The structure is under a temperature change and an electric excitation through the piezoelectric layers. Different distribution patterns of the single walled aligned and straight carbon nanotubes (SWCNTs) through the thickness of the beam are considered. The beam complies with Euler-Bernoulli beam theory and von Kármán geometric nonlinearity. The nonlinearity is due to the mid-plane stretching of the beam and the nonlinear stiffness of the elastic foundation. The Multiple Time Scales perturbation scheme is used to perform the nonlinear dynamical analysis of functionally graded carbon nanotube-reinforced beams. Analytical expressions of the nonlinear natural frequencies, nonlinear dynamic response and frequency response of the system in the case of primary resonance have been presented. The effects of different parameters including applied voltage, temperature change, beam geometry, the volume fraction and distribution pattern of the carbon nanotubes on the nonlinear natural frequencies and frequency-response curves are presented. It is found that the volume fractions of SWCNTs as well as their distribution pattern significantly change the behavior of the system.

Nanohybrid of titania/carbon nanotubes – nanohorns: A promising photocatalyst for enhanced hydrogen production under solar irradiation

Mixtures of straight and defect-free multiwalled carbon nanotubes (MWCNTs), single walled carbon nanohorns (SWCNHs), and multiwalled carbon nanohorns (MWCNHs) were prepared by the arc discharge method. Functionalized Carbon Nanotubes (FCNTs) composed of MWCNTs, MWCNHS and SWCNHs were obtained using acid functionalization process. TiO2/FCNTs (CTP) nanohybrid photocatalysts were obtained with different amounts of FCNTs (2–20 wt%), by wet impregnation method. The photocatalytic activity of both pristine TiO2 as well as the nanohybrids were studied in aqueous glycerol solution under solar irradiation. Reaction parameters such as amount of catalyst and amount of FCNTs in nanohybrids were optimized to ensure high rates of H2 production. With a relatively low amount of pristine TiO2, a high rate of H2 production of 2134 μmol h−1 gcat−1 has been obtained and is likely due to several factors such as well dispersed catalyst, reduced particle–particle agglomeration, resulting in enhanced light absorption (less light shielding), improved separation of charge carriers and utilization for red-ox reactions. Even better results were obtained with the use of nanohybrid catalysts. The enhanced photocatalytic activities of the nanohybrid catalysts are ascribed to the synergetic effects of FCNTs that minimize light reflection which promotes enhanced solar light sensitization, good dispersion of the catalysts in the reaction solution, and improved surface-interface reactions of photogenerated charge carriers. In the present study 10 wt% FCNTs in nanohybrid (CTP-10) exhibited superior photocatalytic activity for H2 generation, nearly 3 times higher than that of pristine TiO2 catalyst. The CTP-10 photocatalyst exhibited photostability under the experimental conditions studied. The nanohybrid photocatalysts were characterized in order to confirm the crystal structure, morphology, surface chemical composition and optical properties. The present work demonstrates the unique beneficial photocatalytic properties of carbon nanotubes and nanohorn mixtures in nanohybrid photocatalysts, for enhanced H2 production.

In search of molecular scale devices: Theoretical study of linearly fused straight single-walled carbon nanotube junctions based on the pentagon/heptagon pair defects

The structural and electronic properties of topological defect of straight intramolecular junctions between two zigzag single-walled carbon nanotubes (SWCNT-IMJ) were studied theoretically. The interfacial junctions can be constructed by fusing two zigzag tubes that differ in helicities and diameters. In the present study, one segment is kept constant by using the (5,0) nanotube, while varying another segment from (6,0) to (10,0). Practically, these (5,0)//(m,0) structures are composed of one or more pentagon/heptagon pairs as “defect” functioning to fuse other perfect hexagonal lattices. It was found that, at the interfacial junctions the 5/7 pair defects induce modified rehybridization of the carbon–carbon networks, which directly affect the geometric and electronic properties. Consequently, the electronic structures are dependent on the variation of diameter and length of carbon nanotubes. Analyses of the electronic structures reveal that the HOMO and LUMO levels exhibit the even–odd “quantum size” oscillation versus varying nanotube chiralities, even with increasing length of nanotubes. The energy gap that indicates metallic or semi-conducting behavior depends on correlation between the tubes indices and tubule length. The NBO analysis has revealed that topological pair defects variation could be an important role for altering the electronic characteristics on these intramolecular junctions. By screening all structures based on their electronic structure diagrams and orbital visualization, we have found that the straight (5,0)//(7,0) junction should be suitable as a molecular rectifying diode. However, other junction structures can also be useful with appropriate tuning of the bias voltage. The outcome of this study would be of help as a knowledge base in the field of carbon nanomaterials molecular electronics.

Vibration Analysis of Randomly Oriented Carbon Nanotube Based on FGM Beam Using Timoshenko Theory

The carbon nanotube (CNT) reinforced functionally graded materials (FGM) are expected to be the new generation materials having wide range of unexplored potential applications in various technological areas such as aerospace and structural and chemical industry. The present work deals with the finite element modeling and free vibration analysis of CNT based functionally graded beam using three-dimensional Timoshenko beam theory. It has been assumed that the material properties of CNT based FG beam vary only along the thickness and these properties are evaluated by rule of mixture. The extended Hamilton principle has been applied to find out the governing equations of CNT based FG beam. Finite element method is used to solve governing equation with the exact shape functions. Initial analysis deals with CNTs assumed to be oriented along the length direction only. But practically it is not possible. So, further work deals with the free vibration analysis of functionally graded nanocomposite beams reinforced by randomly oriented straight single walled carbon nanotubes (SWCNTs). The Eshelby-Mori-Tanaka approach based on an equivalent fiber is used to investigate the material properties of the beam. Results are presented in tabular and graphical forms to show the effects of carbon nanotube orientations, slenderness ratios, and boundary conditions on the dynamic behavior of the beam.

Mixed Navier-layerwise differential quadrature three-dimensional static and free vibration analysis of functionally graded carbon nanotube reinforced composite laminated plates

The three-dimensional free vibration and static analysis of the laminated plates with functionally graded (FG) carbon nanotube reinforced composite (CNTRC) layers is presented using a semi-analytical approach. The individual layers are assumed to be made from a mixture of aligned and straight single-walled carbon nanotubes (CNTs) with volume fractions graded in the thickness direction, and an isotropic matrix. The effective material properties of the resulting FG-CNTRC layers are estimated through a micromechanical model. The through-the-thickness variations of the displacement components are accurately modeled using a layerwise-differential quadrature method, and their in-plane variations are approximated using the trigonometric series. After demonstrating the convergence and accuracy of the method, the effects of geometrical parameters, type of CNTs distribution and volume fractions, and also lamination scheme on the natural frequencies, displacement and stress components of the FG-CNTRC layered plates are investigated.

ストレートタイプ多層カーボンナノチューブ（straight typed MWCNT）のラット13週間全身吸入曝露試験

ストレートタイプ多層カーボンナノチューブ（straight typed MWCNT）のラット13週間全身吸入曝露試験

ストレートタイプ多層カーボンナノチューブ（straight typed MWCNT）の新しい極微量定量法の開発：全身吸入曝露(単回、2週間、13週間)試験の肺中MWCNTの沈着率とその推移

ストレートタイプ多層カーボンナノチューブ（straight typed MWCNT）の新しい極微量定量法の開発：全身吸入曝露(単回、2週間、13週間)試験の肺中MWCNTの沈着率とその推移

Smart damping of fuzzy fiber reinforced composite plates using 1--3 piezoelectric composites

This article is concerned with the investigation of active constrained layer damping (ACLD) of smart laminated fuzzy fiber reinforced composite (FFRC) plates. The distinctive feature of the construction of this novel FFRC is that the uniformly spaced short carbon nanotubes (CNTs) are radially grown on the circumferential surfaces of carbon fibers. The effect of CNT waviness on the damping characteristics of the laminated FFRC plates is investigated when wavy CNTs are coplanar with either of the two mutually orthogonal planes. The constraining layer of the ACLD treatment is made of vertically/obliquely reinforced 1–3 piezoelectric composite material. A finite element model is developed for the laminated FFRC plates integrated with the patches of ACLD treatment. The effects of different boundary conditions of the FFRC plates and orientation angle of piezoelectric fibers on the damping characteristics of the laminated FFRC plates have also been investigated. Results reveal that if the plane of radially grown wavy CNTs on the circumferential surface of carbon fiber is coplanar with the plane of carbon fiber axis then the attenuation of amplitude of vibrations and the natural frequencies of the laminated FFRC plates are significantly improved over those of the FFRC containing straight CNTs or wavy CNTs being coplanar with the transverse plane of carbon fiber.

Effect of CNT waviness on the effective mechanical properties of long and short CNT reinforced composites

Carbon nanotubes (CNTs) possess extremely high stiffness, strength and resilience, and may provide ultimate reinforcing materials for the development of nanocomposites. CNT reinforced composite materials (CNTRC) can be effectively used in aircraft structures, due to their high strength to weight ratio. Accordingly, several experimental and analytical studies have been performed for evaluating effective mechanical properties of CNT-reinforced polymer matrix. However, several complex issues including sizes and forms of CNTs dispersed in a matrix, their distribution and orientation in the matrix make the simulations of the mechanical behaviour of these composites extremely complicated. One such issue is assessing the effect of nanotube curvature since embedded CNTs seldom remain straight inclusions. Nanotube curvature is often characterized by means of the waviness that accounts for the deviation from the straight particles assumption. In this paper, the effect of waviness of CNT is analyzed using a 3-D nanoscale representative volume element (RVE) based on continuum mechanics, and effective elastic modulus is calculated for two cases namely, a RVE with long CNT (CNT throughout the length of RVE) and a RVE with short CNT (CNT completely inside the RVE). Finite element method is used for the analysis. Further, a theoretical model based on the micromechanics of multi-phase composite and energy principles has also been developed to evaluate effective elastic constants of these RVEs. It is found that the reinforcing capacity of the CNTs reduces drastically even with a small waviness as compared to the straight CNTs. The effect of waviness is much more pronounced in case of long wavy CNT than short wavy CNT. The analysis is finally extended to predict the effective moduli of these composites embedded with completely randomly oriented CNTs of different waviness.

Mechanical properties of carbon nanotube ropes with hierarchical helical structures

Hierarchical helical structures widely exist in both artificial and biological materials. Such nanomaterials as carbon nanotube ropes with hierarchical helical structures hold a promise for potential applications, for instance, in aerospace and medical engineering. In the present paper, a bottom-up theoretical model is established to investigate the mechanical properties of this kind of novel nanomaterials. The geometry of a rope with a hierarchy of chirality is first formulated. On the basis of the analysis of the internal forces and deformations of a single helical ply, a theoretical model is provided to predict the mechanical responses of multi-level helical materials. The effect of hierarchical helical structures is revealed by comparing the properties between a carbon nanotube rope with two-level helical structure and its counterpart bundle consisting of straight carbon nanotubes. The dependence of the mechanical properties of materials on the initial helical angles, fiber numbers, and handednesses at different structural levels are examined. Carbon nanotube ropes are found with higher deformation ability and elastic property which can be easily tuned via their microstructural parameters. This work helps understand the behavior of chiral materials and also provides inspirations for optimal design of advanced nanomaterials with hierarchical helical structures.

Peeling of Long, Straight Carbon Nanotubes from Surfaces

The adhesion of long, straight, single-walled carbon nanotubes to surfaces is examined using multidimensional force spectroscopy. We observed characteristic signatures in the deflection and frequency response of the cantilever indicative of nanotube buckling and slip-stick motion as a result of compression and subsequent adhesion and peeling of the nanotube from the surface. The spring constant and the elastic modulus of the SWNT were estimated from the frequency shifts under tension. Using elastica modeling for postbuckled columns, we have determined the static coefficient of friction for the SWNT on alkanethiol-modified gold surfaces and showed that it varies with the identity of the monolayer terminal group.

Finite element simulation of single carbon nanotube pull-outs from a cementitious nanocomposite material using an elastic-plastic-damage and cohesive surface models

Carbon nanotubes (CNTs) have recently been integrated in the most widely used material in the world 'concrete' for improving its mechanical properties and fracture resistance. This paper computationally investigates the pull-out behaviour of a single CNT from cement. The effects of: 1) CNT-cement interfacial shear strength, stiffness, and fracture energy; 2) the cement mechanical properties; 3) CNT's mechanical properties, aspect ratio, and surface area to volume ratio on the pull-out strength from a cement matrix are investigated through simulating the single straight CNT pull-out. A coupled elastic-plastic-damage constitutive model is adopted to simulate the behaviour of the cement matrix, whereas the continuum shell model is used to simulate the elastic behaviour of CNT. The surface-based cohesive behaviour is employed for modelling the interface between CNT and cement matrix. It is shown that CNT pull-out is mainly governed by the interfacial fracture energy, and not the interfacial shear strength.