Effect Of Nanotube Length Research Articles

Effects of the nanotube length and network morphology on the deformation mechanisms and mechanical properties of cross-linked carbon nanotube films

The effects of the carbon nanotube (CNT) length and material structure on the mechanical properties of free-standing thin CNT films with continuous networks of bundles of nanotubes and covalent cross-links are studied in large-scale simulations. The simulations are performed based on a dynamic mesoscopic model that accounts for stretching and bending of CNTs, van der Waals interaction between nanotubes, and inter-tube cross-links. It is found that the tensile modulus and strength of the CNT films strongly increase with increasing CNT length, but the effect of the nanotube length is altered by the cross-link density. The mutual effect of the nanotube length and cross-link density on the modulus and strength is primarily determined by a single parameter that is equal to the average number of cross-links per nanotube. The modulus and strength, as functions of this parameter, follow the power-type scaling laws with strongly different exponents. The film elongation at the maximum stress is dominated by the value of the cross-link density. The dispersion of nanotubes without formation of thick bundles results in a few-fold increase in the modulus and strength. The variation of the film properties is explained by the effects of the CNT length, cross-link density, and network morphology on the network connectivity. The in-plane compression results in the collective bending of nanotubes and folding of the whole film with only minor irreversible changes in the film structure. Depending on the CNT length, the reliefs of the folded films vary from a complex two-dimensional landscape to a quasi-one-dimensional wavy surface.

Vibrational analysis of armchair phosphorene nanotubes by a DFT-based finite element model

A finite element model based upon the density functional theory is developed to investigate the vibrational characteristics of armchair phosphorene nanotubes. To this end, the PP bonds are simulated by beam elements whose elastic properties are obtained from the analogy of molecular and structural mechanics. The effects of nanotube length, diameter and boundary conditions on the frequencies of armchair phosphorene nanotubes are evaluated. It is shown that the effect of nanotube radius on its natural frequency is weakened by increasing the nanotube aspect ratio. Comparing the first ten frequencies of armchair phosphorene nanotubes with different diameters, it is observed that the effect of diameter on the vibrational behavior of phosphorene nanotubes is more pronounced at higher modes.

On the mechanical properties of functionally graded materials reinforced by carbon nanotubes

In this paper, the elastic properties of functionally graded materials reinforced by single-walled carbon nanotubes are studied. Three different matrices, including steel-silicon, iron-alumina and alumina-zirconia are considered. Besides, the effects of nanotube length, radius and volume fraction on the Young’s modulus of functionally graded matrices reinforced by single-walled carbon nanotubes are investigated. It is observed that short nanotubes not only cannot increase the longitudinal elastic modulus of the matrices, but sometimes decrease their elastic modulus. Of the three selected matrices, steel-silicon matrix would have the most enhancement. Investigation of the effect of nanotube volume fraction on the mechanical properties of nanocomposites shows that increasing the volume fraction of long single-walled carbon nanotube results in increasing the elastic modulus of the nanocomposites.

Viscosity and Morphology Modification of Length Sorted Single-Walled Carbon Nanotubes in PIB Matrices

This work evaluates the effectiveness of nanoscale particulates in producing non-Einstein-like responses in polymer matrices, to reduce their negative effects in low shear rate processing. This is of value to material processing applications which encompass extrusion, flow into cold mold, and generalized processing of nanocomposites. Through control and understanding of the structure processing relationships entailed through nanoscale additive materials, we begin to manage dispersion characteristics for more reliable and defect-free product development. In pursuit of identifying system characteristics that produce non-Einstein-like responses we isolate and characterize homogenous fractions of single-walled carbon nanotubes (SWNTs) with singular lengths. This enables the definition of a well-defined nanoscale particulate phase, within the polymer matrices. The effect of nanotube length and weight fraction on the polyisobutylene (PIB) matrices was evaluated with thermal and rheological testing. Our findings show that the viscosity of the produced nanocomposite systems has a length dependence and does not demonstrate the expected monotonous increases in the viscosity with an increase in weight fraction of nanotube additive within the matrix, demonstrating a non-Einstein-like viscosity response. Furthermore, we demonstrate length dependent crystallization in the studied systems, as an intermediate length nanotube initiates crystallization of polyisobutylene (PIB) affecting viscosity and mechanical properties.

Theoretical Study of Atoms Filled in Carbon Nanotubes

The nano-sized quasi-one dimensional hollow cores of carbon nanotubes make it possible for them to be filled with and wetted by foreign materials. With C, S and Se atoms as example, we have studied the filling and wetting of these atoms into carbon nanotubes from local density functional theory in first principles calculations. The results suggest that the effect of nanotube length is negligible when it exceeds 3.6 Å, there is a relation between nanotube diameter and filling and wetting. Our studies would be important implications for the further use of carbon nanotubes.

Analytical and numerical investigations on buckling behavior of nanotube structures

One of the significant issues in the nanotube research community is buckling behavior. In the present work, the buckling of single-walled nanotubes (SWNTs), double-walled nanotubes (DWNTs) and multi-walled nanotubes (MWNTs) under axial compression is investigated. Buckling analysis for nanotube composite structures is performed by using layer-wise theory based on the nonlocal constitutive relations of Eringen. The governing equations of SWNTs, DWNTs and MWNTs are developed. Then analytical solutions are obtained using the state-space method. The effects of nanotube length, diameter and nonlocal parameter on the buckling loads are studied. The numerical results indicate that the nonlocal parameter is important for the buckling analysis of nanotube composite structures.

Biocompatible multi-walled carbon nanotube-chitosan–folic acid nanoparticle hybrids as GFP gene delivery materials

Carbon nanotube (CNT) is one of the inorganic delivery systems that show great potential for optimal biomolecule transporting. Concerning the preparation of CNT-based delivery vectors, it is very important to understand the internal relations of physical properties and surface functionalization of CNTs with the transfection efficiency and cytotoxicity. In this paper, the multi-walled CNTs (MWCNTs) of different length were functionalized with chitosan–folic acid nanoparticles (CS–FA NPs) by ionotropic gelation process. The micromorphologies, surface functional groups, and zeta potential of the MWCNT-CS–FA NPs were characterized. The effects of nanotube length and surface functionalization with CS–FA NPs on the gene transfection efficiency and cytotoxicity were investigated in detail. The non-functionalized MWCNTs and MWCNT-CS–FA NPs all can deliver the plasmid DNA of enhanced green fluorescent protein (pEGFP-N1) into HeLa and MCF-7 cells and the exogenous GFP gene has been expressed. The nanotube length shows a compromise influence on the transfection and cytotoxicity properties of MWCNTs. Having greater gene transfection ability, however, the shorter MWCNTs exhibit larger cytotoxicity than the longer ones. Moreover, the surface functionalization of MWCNTs with CS–FA NPs improves the transfection efficiency and decreases the cytotoxicity as well. Under optimal conditions, the pEGFP-N1 transfection efficiency of MWCNT-CS–FA NPs is about 4.1%, being 1.5 times as large as that of the non-functionalized MWCNTs. The MWCNT-CS–FA NPs show little effect on the cellular viability when the concentration is up to 250μgmL−1. By optimal length control and surface functionalization, MWCNTs should have good applications in gene delivery vectors.

Molecular dynamics simulations of carbon nanotube dispersions in water: Effects of nanotube length, diameter, chirality and surfactant structures

Molecular dynamics simulations are used to compute the potential of mean force (PMF) governing the interactions between carbon nanotubes (CNTs) in water/surfactant systems. The effects of CNT length, diameter, chirality (armchair and zigzag) and surfactant structures on CNT interaction and dispersion in water/surfactant systems are investigated for (5, 5), (5, 0), and (10, 10) single walled CNTs with two commonly used surfactants [viz., sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS)] at room conditions. An adaptive biasing force method was used to speed up the calculations. Simulations revealed that CNT length and diameter as well as optimum amount of surfactant addition and its structures can significantly affect CNT interactions (i.e., PMFs vary significantly). Surfactant molecules were found to adsorb at the CNT surface and reduced interaction strength between CNTs. SDBS surfactant contributed weaker interactions between CNTs as compared with that of SDS surfactant by a factor of about 10 indicating that SDBS is better than SDS for dispersing CNTs in an aqueous suspension. This phenomenon agrees qualitatively with the experimental results reported in the literature. The understanding of detailed atomic arrangements and atomic interactions between CNTs and surrounding molecules reported in this study is significantly helpful to computationally screening different surfactants and improving the CNT dispersion in aqueous solution. The method will also facilitate the reduction of time and cost required to produce CNT reinforced nanocomposite materials as well as homogeneous CNT dispersed solutions for many biological applications.

Effect of nanotube-length on the transport properties of single-file water molecules: Transition from bidirectional to unidirectional

We use molecular dynamics (MD) simulations to study the transport of single-file water molecules through carbon nanotubes (CNTs) with various lengths in an electric field. Most importantly, we find that even the water dipoles inside the CNT are maintained along the field direction, a large amount of water molecules can still transport against the field direction for short CNTs, leading to a low unidirectional transport efficiency (η). As the CNT length increases, the efficiency η will increase remarkably, and achieves the maximum value of 1.0 at or exceeding a critical CNT length. Consequently, the transition from bidirectional to unidirectional transport is observed and is found to be relevant to thermal fluctuations of the two reservoirs, which is explored by the interaction between water molecules inside and outside the CNT. We also find that the water flow vs CNT length follows an exponential decay of f ∼ exp (- L/L(0)), and the average translocation time of individual water molecules yields to a power law of τ(trans) ∼ L(υ), where L(0) and ν are constant and slightly depend on the field strength. We further compare our results with the continuous-time random-walk (CTRW) model and find that the water flow can also be described by a power law of f ∼ L(-μ) modified from CTRW. Our results provide some new physical insights into the biased transport of single-file water molecules, which show the feasibility of using CNTs with any length to pump water in an electric field. The mechanism is important for designing efficient nanofluidic apparatuses.

Pull-out simulations on interfacial properties of carbon nanotube-reinforced polymer nanocomposites

A series of pull-out simulations of carbon nanotube (CNT) has been carried out to investigate the interfacial properties between CNT and polymer matrix for two-phase CNT/polymer nanocomposites with only consideration of van der Waals (vdW) interaction. The effects of nanotube length, diameter, and wall number on the pull-out processes are studied for the first time, which indicates that the pull-out force related to interfacial properties is independent of nanotube length, but is proportional to nanotube diameter. Instead of the conventional constant assumption with uniform distribution, the corresponding interfacial shear stress is found to be distributed at each end of the embedded CNT within the range of 1 nm, which is very close to the cut-off distance of vdW interaction. These characteristics for the interfacial properties between CNT and polymer matrix are surprisingly coincident with those among nested wall in a multi-walled carbon nanotube (MWCNT). Moreover, the saturated surface energy density in CNT/polymer nanocomposites is very close to the previous reports, which indicates the effectiveness of the present simulation.

Thermoelastic damping of a double-walled carbon nanotube under electrostatic force

The quality factor of thermoelastic damping (TED) in a double-walled carbon nanotube (DWNT) under electrostatic actuation is obtained through an analytical method. Each layer of the DWNT is modelled as an Euler Bernouli beam with simply supported boundary conditions. The DWNT is under electrostatic actuation, and van der Waals forces act between layers. The motion equations, coupled with heat equations, are obtained using the Newton's second law, and are then solved using the strained parameter perturbation method. After solving the equations, the presented approach is implemented for a numerical example. The effect of nanotube length and the applied DC voltage on the quality factor of TED are investigated. The quality factor is also studied for different vibration modes of the DWNT. It is shown that shorter DWNTs under higher DC voltages have lower quality factors of TED.

라텍스 기법으로 제조한 폴리스티렌/다중벽 탄소나노튜브 나노복합재료의 나노튜브 길이가 유변학적 특성에 미치는 영향

라텍스 블렌딩 기법을 이용하여 폴리스티렌(PS)/다중벽 탄소나노튜브(MWCNT) 나노복합재료를 제조하여 나노튜브 길이에 따른 나노복합재료의 유변학적 특성을 고찰하였다. 나노복합재료 제조에 사용된 단분산 PS 입자는 무유화제 유화중합으로 제조하였고 NWCNT는 불순물 제거와 분산성 향상을 위해 표면개질 과정을 거친 후 사용하였다. 최종적인 나노복합재료는 단분산 PS 입자와 개질한 MWCNT를 초음파 교반조에서 분산시킨 후 동결건조 과정을 거쳐 제조하였다. 나노복합재료의 MWCNT 함량과 나노튜브 길이에 따른 유변학적 특성은 소진폭 진동 전단유동을 부과시켜 평가하였다. 본 연구에서 고찰한 PS/MWCNT 나노복합재료는 MWCNT의 함량이 증가할수록, 나노튜브 길이가 길수록 유변물성 향상 효과가 뚜렷하였다. 이는 MWCNT 함량이 증가할수록 나노복합재료의 유변학적 특성이 액체적 특성에서 점차 고체적 특성으로 변화하기 때문이며. 나노튜브 길이가 길수록 네트워크 구조를 달성하는 임계 농도가 직아 지지 때문인 것으로 판단된다.

Molecular Dynamics Simulation of Double-Walled Carbon Nanotube Vibrations: Comparison With Continuum Elastic Theories

ABSTRACTDouble-walled carbon nanotubes (DWNTs) are expected to be useful as elements in improving conventional polymer-based fibers and films. An extensive molecular dynamics simulation and continuum analyses are carried out to estimate the influence of matrix stiffness and the intertube radial displacements on free vibration of an individual DWNT. The effects of nanotube length and chirality are also taken into account. The continuum analyses are based on both Euler-Bernoulli and Timoshenko beam theories which considers shear deformation and rotary inertia and for both concentric and non-concentric assumptions considering intertube radial displacements and the related internal degrees of freedom. New intertube resonant frequencies are calculated. Detailed results are demonstrated for the dependence of resonant frequencies on the matrix stiffness. The results indicate that internal radial displacement and surrounding matrix stiffness could substantially affect resonant frequencies especially for longer doublewalled carbon nanotubes of larger innermost radius at higher resonant frequencies, and thus the latter does not keep the otherwise concentric structure at ultrahigh frequencies.

Effect of Nanotube Length on the Aromaticity of Single-Wall Carbon Nanotubes

The aromaticity properties of single-wall carbon nanotubes are investigated using density functional theory to determine the nucleus independent chemical shift at the open end of one-end-closed nanotubes and two-ends-open nanotubes. Two chiralities: near-arm-chair (6,5) and near-zigzag (9,1) nanotubes of identical diameter and each one having a unique cap compatible with their structure are examined for a comparison of their aromatic properties and the influence of the presence of the cap on such properties. The influence of the cap structure is also analyzed on the (8,3) nanotube having a larger diameter and being compatible with three different caps. We conclude that the presence of the cap and the specific chirality provide distinct aromaticity and reactivity properties to single-wall carbon nanotubes, whereas for a given chirality the particular nature of the cap seems to be of no relevance for these properties.

Mechanisms of nanoindentation on single-walled carbon nanotubes: The effect of nanotube length

The mechanisms of nanoindentation on single-walled carbon nanotubes (SWCNTs) have been studied by using molecular dynamics simulation and continuum analysis during which a flat layer of diamond atoms is pressed down incrementally on a vertically aligned SWCNT. SWCNTs are divided into three distinct categories based on their aspect ratios, such that the nanotube behavior transits from a shell (short tube) to a beam (long tube). Molecular dynamics simulations are used to explore the diverse indentation characteristics in each domain, where the relationships between the strain energy and indentation depth during loading, unloading, and reloading are continuously recorded. The nanoindentation mechanisms are characterized by the critical indentation depth, maximum strain energy and force associated with buckling, as well as with the evolution of carbon bond length and morphology of the SWCNTs. Bifurcation behaviors are explored by investigating the loading-unloading-reloading behaviors of the nanotubes. Parallel finite element simulations are also used to study the pre- and post-buckling behaviors of SWCNT by incorporating the van der Waals interaction into the continuum code. It is found that, for the most part, continuum analysis can effectively capture the overall indentation characteristics, yet some details related to the atomic characteristics of nanoindentation may only be revealed by molecular dynamics simulation. Finally, an indentation mechanism map is derived by comparing behaviors of SWCNTs with different aspect and section ratios. Focusing on the effects of nanotube length, this paper is the first of a series of numerical studies on the indentation mechanisms of carbon nanotubes, which may be used to determine the intrinsic mechanical properties of SWCNTs by means of nanoindentation.

Axial and radial thermal expansions of single-walled carbon nanotubes

This paper examines the thermal expansion of single-walled carbon nanotubes. The vibrational frequencies of carbon atoms are calculated by applying the molecular structural mechanics approach. The entropy of a nanotube is obtained by the quantization of vibrational frequencies. The coefficients of thermal expansion (CTE) of single-walled carbon nanotubes in the axial and radial directions are then obtained by the differential of entropy with respect to the applied pressure. The computational results indicate that both the axial and radial CTEs are positive and increase with increasing temperature. The nanotube diameter has an insignificant effect on the axial thermal expansion. But the radial thermal expansion increases significantly with increasing tube diameter. The effect of nanotube length on radial CTE is larger than that on axial CTE and becomes more pronounced at high temperatures. The nanotube chirality has a slight effect on both of the axial and radial CTEs.

The Study on the Filling of Atoms in a Carbon Nanotube

The filling of Pb, C, Al and S atoms into Carbon nanotubes is studied by use of the discrete variational method within the local density functional theory. It is found that Lead atom inclines to enter into tubes, while Carbon atom rather stays at the mouth of nanotubes, which is in good agreement with experiments. The effect of nanotube length and diameter on the filling is discussed.