Mechanical Properties Of Carbon Nanotubes Research Articles

Modelling and analysis of mechanical behaviour of carbon nanotube reinforced composites

In this paper, the mechanical properties of carbon nanotube reinforced composites are evaluated based on the continuum mechanics approach using a hexagonal representative volume element (RVE) under lateral loading conditions. It is paramount in such analyses that the correct boundary conditions be imposed, such that they simulate the actual deformation within the composite. Numerical equations are used to evaluate the mechanical properties from numerical solutions for the hexagonal RVEs under the lateral load case. An extended rule of mixtures is applied to evaluate the effective axial Young’s modulus, for validation of the proposed model. For the RVEs having long carbon nanotube, better values of stiffness in axial direction are found as compared to stiffness in the lateral direction. Also, the comparative evaluation of both square and hexagonal RVEs with short carbon nanotubes is presented here. The short carbon nanotube is not found to be as effective as long carbon nanotube in reinforcing the composite.

Description of mechanical properties of carbon nanotubes. Tube wall thickness problem. Size effect. Part 2

This paper is a continuation of Part 1 [1], using the method of the atomic modeling with the potential of Tersoff-Brenner-Stewart to describe the mechanical properties of single-walled carbon nanotubes (SWCNTs). Large scale effect was found for the mechanical properties of nanotubes with diameters of several nanometers. A significant difference in the properties of nanotubes such as "zigzag" and "chair" is set, i.e. helicity of the atomic structure is essential. The difference in elasticity in tension and compression of nanotubes (bi-modulus effect) is detected. Scaling instability effect of nanotubes in compression is identified.<br />

Non-covalent interactions between carbon nanotubes and conjugated polymers

Carbon nanotubes (CNTs) are interest to many different disciplines including chemistry, physics, biology, material science and engineering because of their unique properties and potential applications in various areas spanning from optoelectronics to biotechnology. However, one of the drawbacks associated with these materials is their insolubility which limits their wide accessibility for many applications. Various approaches have been adopted to circumvent this problem including modification of carbon nanotube surfaces by non-covalent and covalent attachments of solubilizing groups. Covalent approach modification may alter the intrinsic properties of carbon nanotubes and, in turn make them undesirable for many applications. On the other hand, a non-covalent approach helps to improve the solubility of CNTs while preserving their intrinsic properties. Among many non-covalent modifiers of CNTs, conjugated polymers are receiving increasing attention and highly appealing because of a number of reasons. To this end, the aim of this feature article is to review the recent results on the conjugated polymer-based non-covalent functionalization of CNTs with an emphasis on the effect of conjugated polymers in the dispersibility/solubility, optical, thermal and mechanical properties of carbon nanotubes as well as their usage in the purification and isolation of a specific single-walled nanotube from the mixture of the various tubes.

Joining carbon nanotubes

To fully exploit the exceptional electronic and mechanical properties of carbon nanotubes in real-world applications, it is desirable to create carbon nanotube networks in which separate, multiple nanotubes are joined so that as many as possible of the properties of single nanotubes are conserved. In this review we summarize the progress made towards this goal, covering techniques including electron and ion beam irradiation, Joule heating and spark plasma sintering.

Description of mechanical properties of carbon nanotubes. Tube wall thickness problem. Size effect. Part 1

The classical theory of elasticity is used to describe the mechanical properties of nanotubes in many publications. However, necessary for applicability of the theory of elasticity conditions are not fulfilled in the case of single-walled carbon nanotubes (SWCNTs) and tubes with a small number of atomic layers in their walls. Therefore, in the first part of this article, we introduce the method of molecular dynamics and general energy analysis for the description of the generalized Young's modulus (with the dimension of the surface stiffness) and Poisson's ratio characterizing the uniaxial tension of SWCNTs. The strong dependence of the generalized characteristics of the studied nanoscales is their distinctive feature (size effect) as in the contrast to the similar concepts of the elasticity theory. <br /> Here in Part 1 we discussed features of the basic approach and the using of the semi-empirical Tersoff-Brenner-Stewart potential. The main findings will be presented in Part 2.<br /> <br />

What is the role of defects in single-walled carbon nanotubes for nonlinear optical property?

In carbon nanotubes (CNTs), there exist various kinds of defects which may influence the electrical, thermal and mechanical properties of carbon nanotubes. However, how the defect influences the nonlinear optical (NLO) property is still unknown. This paper exhibits the role of defects on the static first hyperpolarizability (β0) for topological Stone-Wales (SW), single vacancy (SV) and double vacancy (DV) defects. For eight carbon nanotubes with defects and one relevant perfect nanotube, the obtained order of the β0 values is 0 (Perfect) < 5.0 × 102 (DV585-z) < 5.3 × 102 (SW5577-z) < 4.6 × 103 (DV585-xz) < 6.0 × 103 (DV555777) < 7.3 × 103 (SV-xz) < 1.1 × 104 (SV-z) < 3.3 × 104 (SW5577-xz) < 2.2 × 105 a.u. (SW57-75). The results show that the defect plays an important role on greatly enhancing the β0 value due to lowering the transition energy. Four interesting relationships between the defect and the β0 value are observed. (1) The defects bring a large increase of the β0 values. (2) For the SW and DV defects, the direction of the defect is an important factor to enhance the β0 value. For example, β0 values of SW5577 structures are 3.3 × 104 (near xz direction) ≫ 5.3 × 102 a.u. (the z direction along the tube axis). (3) Interestingly, not vacancy defects but the topological defect can bring the largest β0 value (2.2 × 105 a.u. for the SW57-75). (4) For the topological SW defects, the separate pentagon-heptagon pair defect (57–75, the β0 value of 2.2 × 105 a.u.) may be more efficient than the fused one (5577, 3.3 × 104 a.u.) to enhance the β0 value. This work suggests a new strategy, introducing the right defect on CNTs to enhance the nonlinear optical response.

Processing of yttria stabilized zirconia reinforced with multi-walled carbon nanotubes with attractive mechanical properties

The improvement of the mechanical properties of carbon nanotube reinforced polycrystalline yttria-stabilized zirconia (CNT–YSZ) was questionable in earlier investigations due to several difficulties for processing of these composites. In the present article, the authors are proposing a successful technique for mixing pre-dispersed CNTs within YSZ particles followed by a fast spark plasma sintering at relatively low temperature, resulting in near full-dense structure with well-distributed CNTs. Composites with CNT quantities ranging within 0.5–5 wt% have been analyzed and a significant improvement in mechanical properties, i.e. Young's modulus, indentation hardness and fracture toughness with respect to monolithic YSZ could be observed. To support these interesting mechanical properties, high-resolution electron microscopy and Raman spectroscopy measurements have been carried out. The analysis of densification shows that the lower densification rate of CNT reinforced composites with respect to the pure YSZ could be attributed to a slower grain boundary sliding or migration during sintering.

Effect of Nitrogen Doping on the Mechanical Properties of Carbon Nanotubes

We report on the usage of a simple microfabricated device that works in conjunction with a quantitative Nanoindenter within a scanning electron microscope (SEM) chamber, for the in situ quantitative tensile testing of individual catalytically grown pristine and nitrogen-doped multiwall carbon nanotubes (MWNTs). The two types of MWNTs were found to possess similar strengths but different load-bearing abilities owing to the differences in their wall structures. Also, stress versus strain curves and fracture surfaces showed that while the pristine MWNTs deform and fail in a brittle fashion, the nitrogen-doped MWNTs deform plastically to varying degrees prior to failure. High resolution transmission electron microscope (TEM) images of the nitrogen-doped MWNT fracture specimens showed the presence of regions of reduced cross-section areas and kinks in close proximity to the fracture surfaces. The presence of nitrogen atoms in the graphitic sheets was assumed to have led to the formation of kinks whose motion induced by straining could have resulted in the plastic deformation of the carbon nanotubes.

PH-Controlled Carbon Nanotube Aggregation/Dispersion Based on Intermolecular I-Motif DNA Formation

In this work, we report a new strategy to manipulate the aggregation and dispersion of carbon nanotube in solution via formation of intermolecular i-motif (four-stranded C-quadruplex) structures in a pH dependent manner. Firstly, single-stranded (ss) DNAs containing two stretches of cytosine (C)-rich domains are covalently linked to carbon nanotubes. At pH 8.0, DNAs are at random coil state, which enhance the dispersion of multi-wall carbon nanotubes (MWNTs) in water; after changing pH to 5.0, the intermolecular i-motif structures formed by the C-rich ssDNAs on neighboring carbon nanotube could drive the MWNTs aggregate. This process is reversible and the transition process has been verified by circular dichroism (CD) spectroscopy, gel electrophoresis and transmission electron microscopy (TEM). Considering the mechanical properties of carbon nanotube, this finding will benefit many application research fields, such as artificial muscle, functional nano-devices and so on.

Stochastic multi-scale modeling of CNT/polymer composites

A full stochastic multi-scale modeling technique is developed to estimate mechanical properties of carbon nanotube reinforced polymers. Developing a full-range multi-scale technique to consider effective parameters of all nano, micro, meso and macro-scales and full stochastic implementation of integrated modeling procedures are the novelties of the present research. The length, orientation, agglomeration, curvature and dispersion of carbon nanotubes are taken into account as random parameters. It is proven that random distribution of carbon nanotube length and volume fraction can be replaced with corresponding mean values. The results of predictions are in a very good agreement with published experimental observations.

Evaluation of the Mechanical Properties of CNT Based Composites Using Hexagonal RVE

Carbon nanotubes (CNTs) possess extremely high stiffness, strength, and resilience, and may provide ultimate reinforcing materials for the development of nanocomposites. In this paper, the effective material properties of CNT-based composites are evaluated based on the continuum mechanics using a hexagonal representative volume element (RVE). Numerical equations are used to extract the effective material properties from numerical solutions for the hexagonal RVEs under axial loading case. An extended rule of mixtures for estimating effective Young’s modulus in the axial direction of the RVE is applied. It has been observed that the addition of the CNTs in a matrix at volume fractions of only about 3.6%, the stiffness of the composite is increased by 33% for long CNT at Et/Em=10, whereas not much improvement in stiffness has been noticed in the case of short CNTS at Et/Em=10. Effectiveness of composites is evaluated in terms of various dimensions such as thickness, diameter, and length of CNT. These results suggest that short CNTs in a matrix may not be as effective as long CNTs in reinforcing a composite. The simulation results are consistent with the experimental ones reported in literature. Also, the comparative evaluation of all three types of RVEs is presented here.

Multiscale analysis of carbon nanotube-reinforced nanofiber scaffolds

Abstract Biopolymers play a significant role in tissue engineering, as they simulate the physiological environment required for the development of tissue cultures. Use of carbon nanotube polymeric scaffolds for tissue engineering applications has gained attention recently due to the enhanced mechanical properties of carbon nanotubes. In this paper, a hierarchical approach by studying the atomistic properties of carbon nanotube based polymers using molecular dynamics and coupling the scales through complex multi-scale nonlinear hyperelastic material-based mathematical homogenization models are developed. These homogenization methods offer a systematic and rigorous treatment of up-scaling the properties from the micro or nanoscale to the macroscales. The material constitutive properties estimated using the developed methods for nanotube polymeric scaffold materials show excellent comparison with experimental studies.

STUDY OF PRISTINE CARBON NANOTUBE UNDER TENSILE AND COMPRESSIVE LOADS USING MOLECULAR DYNAMICS SIMULATION

After the discovery, carbon nanotubes (CNTs) have received tremendous scientific and industrial interests. This is due to their exceptional mechanical, electrical, and thermal properties. CNTs having pristine structure (i.e., structure without any defect) hold very high mechanical properties. In this article, mechanical properties of CNTs are studied under both tensile and compressive loads using molecular dynamics (MD) simulations. Four armchair single-walled nanotubes (SWNTs) having indexes of (3,3), (4,4), (5,5) and (6,6) with pristine structure are simulated with MD. Molecular simulations are carried out using the classical MD method, in which the Newtonian equations of motion are solved numerically for a set of atoms. The velocity- Verlet algorithm is used for solving the Newtonian equations of motion. The Brenner potential is used for carbon-carbon interaction in the CNT and temperature of the system is controlled by velocity scaling. Simulation results show that modulus of elasticity of CNTs varies significantly with CNT diameter. The results obtained from the compressive test by MD simulations are in well agreement with the results obtained from theoretical Euler equation and parabolic equation for long and short column respectively.Keywords: Carbon nanotubes; Molecular dynamics; Young’s modulus; Failure strength; Failure strain.DOI: 10.3329/jme.v40i2.5346Journal of Mechanical Engineering, Vol. ME 40, No. 2, December 2009 72-78

Highly dispersed carbon nanotube reinforced cement based materials

The remarkable mechanical properties of carbon nanotubes (CNT) suggest that they are ideal candidates for high performance cementitious composites. The major challenge however, associated with the incorporation of CNTs in cement based materials is poor dispersion. In this study, effective dispersion of different length multiwall carbon nanotubes (MWCNTs) in water was achieved by applying ultrasonic energy and in combination with the use of a surfactant. The effects of ultrasonic energy and surfactant concentration on the dispersion of MWCNTs at an amount of 0.08 wt.% of cement were investigated. It is shown that for proper dispersion the application of ultrasonic energy is absolutely required and for complete dispersion there exists an optimum weight ratio of surfactant to CNTs. For a constant ratio of surfactant to MWCNTs, the effects of MWCNT type (short and long) and concentration on the fracture properties, nanoscale properties and microstructure of nanocomposite materials were also studied. Results suggest that MWCNTs improve the nano- and macromechanical properties of cement paste.

Modified embedded atom method study of the mechanical properties of carbon nanotube reinforced nickel composites

We report an atomistic simulation study of the behavior of nanocomposite materials that are formed by incorporating single-walled carbon nanotubes SWCNTs, with three different diameters, and a multiwalled carbon nanotube MWCNT into a single-crystal nickel matrix. The interactions between carbon and nickel atoms are described by a modified embedded atom method potential. Mechanical properties of these nanocomposite materials are predicted by atomistic calculations and compared with that of fcc nickel and pristine CNTs. Our simulations predict that all Ni/CNT composites studied in this work are mechanically stable. Their elastic properties depend on the volume fraction and diameter of embedded CNTs. The single-crystal Young’s modulus E11 of Ni/SWCNT composites exhibit a large increase in the direction of CNTs alignment compared to that of a single-crystal nickel. However, a moderate but gradual decrease is seen for E22 and E33 in the transverse directions with increase in CNT diameters. As a consequence, Ni/SWCNTs show a gradual decrease for the polycrystalline Young’s, bulk and shear moduli with the increasing CNT diameters and volume fractions. These reductions, although moderate, suggest that enhancement of mechanical properties for polycrystalline Ni/SWCNT nanocomposites are not achievable at any CNT volume fraction. The Ni/MWCNT composite with high CNT volume fraction shows the highest increase in E11. Unlike the E22 and E33 for Ni/ SWCNTs, there is a significant increase in the E22 and the E33 for Ni/MWCNT. As a result, polycrystalline Ni/MWCNT composites show slight increase in the elastic properties. This suggests that nickel nanocomposites with enhanced mechanical properties can be fabricated using large volume fractions of larger diameter MWCNTs. Depending on type, alignment and volume fraction, Ni/CNT composites show varying degrees of elastic anisotropy and Poisson’s ratio compared to pure Ni. Simulation predicts strong adhesion at the Ni/CNT interface and a significant interfacial stress transfer between CNT and Ni matrix.

Equivalent Continuum Models for the Simulation of Mechanical Properties of Carbon Nanotube by Global-Local Homogenization Method

In this paper, the global-local homogenization method is applied for two kinds of equivalent continuum models to analyze the effective mechanical properties of single-walled carbon nano tube (CNT). The material and geometric parameters are provided by equating the molecular potential energy of nano-structure material with the strain energy of equivalent continuum tube and equivalent continuum frame. The results show that global-local homogenization method is effective to investigate the mechanical properties of single-walled nano-structure with a reasonable selection for equivalent continuum models (representative volume element RVE). The variations of the effective Young’s modulus with chiral parameters, thickness of models and poisson’s ratio of carbon nanotube are discussed for both zig-zag and armchair configurations. Comparing with the results from other classical methods, the homogenization method with equivalent continuum models can give moderate and stable results.

Radial mechanical properties of single-walled carbon nanotubes using modified molecular structure mechanics

This study presents a modified molecular structure mechanics (MSM) model for determining the mechanical properties of carbon nanotubes, particularly in the radial direction. In the proposed model, the interactions between two carbon atoms are modeled with the second generation force field using continuum pseudo-rectangular beam elements while the non-bonded van der Waals (vdW) interactions among atoms are simulated with the Lennard–Jones (L–J) potential using spring elements. The pseudo-rectangular beam consists of a different bending rigidity along the two principal centroidal axes of the cross-section, the stiffness parameters of which are estimated based on the bond-angle variation energy and the weak inversion energy in molecular mechanics. By the approach, the mechanical properties of single-walled carbon nanotubes (SWCNTs), in particular the radial modulus, radial buckling load, and radial deformation, are calculated. To demonstrate the effectiveness of the proposed MSM model, the derived results are compared with those of the original MSM model and the published theoretical and experimental data. Results show that the radial elastic modulus of the zigzag SWCNTs with a radius of 0.39–2.35 nm is about 62–0.4 GPa through the proposed MSM model, and that of the armchair SWCNTs with a radius of 0.48–2.38 nm is about 30–0.3 GPa. The results are considerably less than those of the original MSM model but much more consistent with the literature data. Even the weak vdW interactions may potentially result in remarkable radial collapse or deformation of the SWCNTs as their radius is larger than about 1.1 nm. Besides, it is also demonstrated that the modification would have a little effect on the axial Young’s modulus and Poisson’s ratio.

Compressive mechanical properties of carbon nanotubes encapsulating helical copper nanowires

Molecular dynamics combined with continuum mechanics is utilized to predict the compressive mechanical properties of carbon nanotubes encapsulating helical copper nanowire (NW@CNTs). The helical structures of the copper nanowires are obtained using the “simulated annealing” method. The compressive behaviors of this kind of composites are studied. The strain energy curves are shown to predict the interaction between the atoms during the compressive course. This model can be used effectively to determine the mechanical properties such as the critical buckling load Pcr and the Young’s moduli of NW@CNTs with different diameters and lengths. We also find that not all the maximum strengths of the composites are larger than the corresponding carbon nanotube bases, and they are related with the diameter, length and the carbon nanotube’s chirality. According to the comparison with the pristine carbon nanotubes (CNTs), some excellent properties of NW@CNTs are revealed.

Enhancement of Friction between Carbon Nanotubes: An Efficient Strategy to Strengthen Fibers

Interfacial friction plays a crucial role in the mechanical properties of carbon nanotube based fibers, composites, and devices. Here we use molecular dynamics simulation to investigate the pressure effect on the friction within carbon nanotube bundles. It reveals that the intertube frictional force can be increased by a factor of 1.5-4, depending on tube chirality and radius, when all tubes collapse above a critical pressure and when the bundle remains collapsed with unloading down to atmospheric pressure. Furthermore, the overall cross-sectional area also decreases significantly for the collapsed structure, making the bundle stronger. Our study suggests a new and efficient way to reinforce nanotube fibers, possibly stronger than carbon fibers, for usage at ambient conditions.

Synthesis and mechanical properties of carbon nanotubes produced by the water assisted CVD process

AbstractCatalyst activity during the carbon nanotubes (CNTs) growth by chemical vapor deposition (CVD) is enhanced when water, a weak oxidizer, is introduced together with the carbon source. The height as well as the CNTs density can be controlled by fine‐tuning the water content. The characterization of the mechanical properties of CNTs produced by the water assisted CVD process clearly indicates that high quality materials are produced. CNTs with diameter smaller than 12 nm exhibit Young's modulus higher than 400 GPa.