Mechanical properties of nickel-coated single-walled carbon nanotubes and their embedded gold matrix composites

The effects of nickel coating on the mechanical behaviors of armchair single-walled carbon nanotubes (SWCNTs) and their embedded gold matrix composites under axial tension are investigated using molecular dynamics (MD) simulation method. The results show that the Young's moduli and tensile strength of SWCNTs obviously decrease after nickel coating. For armchair SWCNTs, the decreased ratio of the Young's moduli of SWCNTs with smaller radius is larger than that of SWCNTs with larger radius. A comparison is made between the response to Young's modulus of a composite with parallel embedded nanotube and the response of a composite with vertically embedded nanotube. The results show that the uncoated SWCNT can enhance the Young's modulus of composite under the condition of parallel embedment, but such improvement disappears under the condition of vertical embedment because the interaction between SWCNT and gold matrix is too weak for effective load transfer. However, the nickel-coated SWCNT can indeed significantly improve the composite behavior.     

Designing different nanomagnets via delocalization of cobalt magnetic moment inside narrow single walled carbon nanotubes

Density functional theory calculations were employed to study the effects of chirality and diameter of single walled carbon nanotubes (SWCNTs) on electronic, structural and magnetic properties of cobalt-doped (9,0), (5,5) and (5,0) nanotube systems. The (9,0) and (5,5) SWCNTs have similar diameters but different chiralities, whereas the (5,0) tube has a very small diameter. The Co-SWCNT systems are considered with four different possible arrangements, three of which are stable and only substitution of the Co with one of the carbon atoms on the surface of the SWCNTs is an exemption. Although the quasi-metallic band gap of the (9,0) SWCNT is eliminated by the cobalt doping process, metallic features of the (5,5) and (5,0) nanotubes remain unchanged. On the other hand, delocalization of the cobalt’s magnetization and inducement of a noticeable magnetization to the tubes provide a vast area of possible total magnetizations for the Co-SWCNT systems. The results are applicable to spintronics and useful for designing other nanomagnetic systems.     

Compressive characteristics of single walled carbon nanotube with water interactions investigated by using molecular dynamics simulation

The elastic properties of single walled carbon nanotube (SWCNT) with surrounding water interactions are studied using molecular dynamics simulation technique. The compressive loading characteristic of carbon nanotubes (CNTs) in a fluidic medium such as water is critical for its role in determining the lifetime and stability of CNT based nano-fluidic devices. In this paper, we conducted a comprehensive analysis on the effect of geometry, chirality and density of encapsulated water on the elastic properties of SWCNT. Our studies show that defect density and distribution can strongly impact the compressive resistance of SWCNTs in water. Further studies were conducted on capped SWCNTs with varying densities of encapsulated water, which is necessary to understand the strength of CNT as a potential drug carrier. The results obtained from this paper will help determining the potential applications of CNTs in the field of nano-electromechanical systems (NEMS) such as nano-biological and nano-fluidic devices.     

Molecular dynamics study on resonance frequency change due to axial-strain-induced torsions of single-walled carbon nanotubes

We investigated, via the classical MD simulation method based on Tersoff-Brenner potential, the fundamental resonance frequency changes of single-walled carbon nanotube (SWCNT) resonators originated from the purely mechanical coupling of the axial-strain-induced torsion (ASIT) response. The fundamental frequency changes were also negligible where the ASIT responses were negligible in achiral SWCNTs whereas those were explicitly found under both compression and tension for the chiral SWCNTs with the obvious ASIT responses. Specially, for SWCNT with the chiral angle of π/12, where the highest ASIT response can be found, the fundamental resonance frequency changes were highest. The fundamental resonance frequencies under the tensioning increased almost linearly with increasing the axial strain whereas they rapidly decreased under compression with increasing the compressive strain.     

Mechanism of Carbon Nanotubes Aligning along Applied Electric Field

The mechanism of single-walled carbon nanotubes （SWCNTs） aligning in the direction of external electric field is studied by quantum mechanics calculations. The rotational torque on the carbon nanotubes is proportional to the difference between the longitudinal and transverse polarizabilities and varies with the angle of SWCNTs to the external electric field. The longitudinal polarizability increases with second power of length, while the transverse polarizability increases linearly with length. A zigzag SWCNT has larger longitudinal and transverse polarizabilities than an armchair SWCNT with the same diameter and the discrepancy becomes larger for longer tubes.     

Radial collapse and physical mechanism of carbon nanotube with divacancy and 5-8-5 defects

By employing molecular mechanics and molecular dynamics simulations, we investigate the radial collapses and elasticities of different chiral single-walled carbon nanotubes(SWCNTs) with divacancy, and 5-8-5 defects. It is found that divacancy and 5-8-5 defect can reduce the collapse pressure(Pc) of SWCNT(10, 10) while 5-8-5 defect can greatly increase Pc of SWCNT(17, 0). For example, 5-8-5 defect can make Pc of SWCNT(17, 0) increase by 500%. A model is established to understand the effects of chirality, divacancy, and 5-8-5 defect on radial collapse of SWCNTs. The results are particularly of value for understanding the mechanical behavior of SWCNT with divacancy, and the 5-8-5 defect that may be considered as a filler of high loading composites.     

Molecular Dynamics Study of Effects of Si-Doping Upon Structure and Mechanical Properties of Carbon Nanotube

In this paper, a Si-doped single-walled carbon nanotube (SWCNT) (7,7) and several perfect armchair SWCNTs are investigated using the classical molecular dynamics simulations method. The inter-atomic short-range interaction is represented by empirical Tersoff bond order potential. The computational results show that the axial Young's modulus of the perfect SWCNTs are in the range of 1.099 ± 0.005 TPa, which is in good agreement with the existing experimental results. From our simulation, the Si-doping decreases the Young's modulus of SWCNT, and with the increased strain levels, the effect of Si-doped layer in enhancing the local stress level increases. The Young's modulus of armchair SWCNTs are weakly affected by tube radius.     

Exploring the simultaneous existence of Stone-Wales and carbon ad-dimer defects in the zigzag single-walled carbon nanotubes

We have applied density functional calculations to investigate simultaneous existence of Stone–Wales (SW) and carbon ad-dimer (CD) defects in the zigzag (n, 0) n=5, 6, 7, 8, 9, and 10 SWCNTs, with an extensive search by considering two different orientations of defects. According to our results, the adsorption of a carbon dimer on a hexagonal ring of SWCNTs is easier than the rotation of a C–C bond trough the SW rearrangement. Moreover, the formation of a carbon dimer on the exterior sidewalls of an SW defective SWCNT or the rotation of a C–C bond of a CD defective SWCNT is more favorable than those on the perfect ones. Defect formation energy shows a strong dependence on the both SWCNT radius and defect orientation. The reactivity of SW–CD defective SWCNTs through chemisorption of hydrogen atoms on the central bonds of defect sites shows the thermodynamically lower preference of additions for the CD defective sites in comparison to SW defective sites. Histograms of the ¹³C NMR chemical shifts of SW–CD defective SWCNTs exhibit individual signals for defect sites, which can be attributed to azupyrene- and pentalelene-like structures for SW and CD defect sites, respectively.     

Consideration of mechanical properties of single-walled carbon nanotubes under various loading conditions

In this article, mechanical properties of single-walled carbon nanotubes (SWCNTs) with various radiuses under tensile, compressive and lateral loads are considered. Stress–strain curve, elastic modulus, tensile, compressive and rotational stiffness, buckling behaviour, and critical axial compressive load and pressure of eight different zigzag and armchair SWCNTs are investigated to figure out the effect of radius and chirality on mechanical properties of nanotubes. Using molecular dynamic simulation (MDS) method, it can be explained that SWCNTs have higher Young’s modulus and tensile stiffness than compressive elastic modulus and compressive stiffness. Critical axial force of zigzag SWCNT is independent from the radius, but that of armchair type rises by increasing of radius, also these two types show different buckling modes.     

曲率对Rh在锯齿型单壁碳纳米管内外吸附影响的研究

利用密度泛函理论系统的研究了单壁碳纳米管的曲率对Rh原子在锯齿型碳管内外的吸附行为, 发现Rh原子在管外吸附比管内稳定; 随着碳管管径的增加, 曲率减小, 管内外吸附能的差值逐渐减小, 接近Rh原子在石墨烯上的吸附能. 电荷密度分析表明, 由于卷曲效应使碳纳米管管外的电荷密度大于管内, 随着曲率减小, 这种差别逐渐减小. 管内外吸附Rh原子的Bader电荷差值及局域态密度差别亦随着曲率的下降而减小, 这与Rh原子在管内外吸附能的变化规律相一致.     

光谱法研究水溶性羧基化碳纳米管与人血清白蛋白的相互作用

纳米材料与蛋白质等生物大分子的相互作用是纳米材料生物效应和安全性研究的重要基础。本实验利用荧光光谱、同步荧光光谱、圆二色谱(CD)等方法研究了四种结构特性不同的水溶性羧基化碳纳米管(long-SWCNTs-COOH,short-SWCNTs-COOH,DWCNTs-COOH,MWCNTs-COOH)与人血清白蛋白(human serum albumin, HSA)的相互作用。实验结果显示：四种水溶性羧基碳纳米管均能猝灭HSA的内源荧光,但猝灭能力有所不同,相同浓度下不同水溶性羧基化碳纳米管对HSA的荧光猝灭作用遵循如下规律：DWCNTs-COOH＜MWCNTs-COOH＜long-SWCTs-COOH＜short-SWCNTs-COOH;四种碳纳米管对HSA的同步荧光光谱影响表明,MWCNTs-COOH的作用位点更靠近色氨酸(Trp)残基,而DWCNTs-COOH的作用位点更靠近酪氨酸(Tyr)残基,而long-SWCNTs-COOH和short-SWCNTs-COOH对两种氨基酸残基的作用无明显差别;在碳纳米管作用下,HSA 的圆二色谱有微弱的变化,且与α-螺旋、β-折叠含量变化基本一致。结果表明,不同碳纳米管对HSA的荧光猝灭能力与它们的结构特性有关,两者作用过程中HSA构象基本不变,二级结构有微小变化,但无明显的剂量-效应关系。根据实验结果对可能的作用机制进行了讨论。     

单壁碳纳米管拉伸变形的原子尺度模拟

采用分子动力学方法对单壁碳纳米管的拉伸变形行为进行了模拟,结果表明,碳纳米管具有较高的断裂应变.在结构产生缺陷之前,碳纳米管表现出弹性变形的特征.通过对能量变化的分析可以看出,能量分布的不均匀是导致结构失稳产生缺陷的主要因素.通过对含初始结构缺陷的碳纳米管在拉伸变形过程中的构型变化进行分析,发现在缺陷附近原来相邻的两个六边形蜂窝结构,随着拉伸变形的发展转变成5 7结构(Stone Wales转变),能量产生突变,应变能的释放使系统能量降低.分析也表明,较少数目的初始缺陷对碳纳米管的力学性质并不会有太大影响.     

Torsional mechanics of single walled carbon nanotubes with hydrogen for energy storage and fuel cell applications

Torsional mechanics of single walled carbon nanotubes(SWCNTs) encapsulated with hydrogen molecules was investigated in this study, using the molecular dynamics(MD) simulation approach. The torsional properties of hydrogen stored SWCNTs were crucial for determining the durability and lifetime of SWNCTs-based energy storage and proton exchange membrane fuel cell(PEMFC) applications. The influence of hydrogen storage concentration, SWCNT geometry, vacancy defects, temperature variation and varying boundaries of rotated as well as fixed groups on the torsional mechanics of SWCNT was investigated. The results and conclusions provide an insight into the torsional properties of SWCNTs with hydrogen storage that could be used for the development of SWCNTs-based hydrogen storage devices and PEMFC applications.     

Liquid dimethyl sulphoxide confined by carbon nanotubes

Here, we report the molecular dynamics simulation on liquid dimethyl sulphoxide (DMSO) confined by single-walled carbon nanotubes (SWCNTs) in comparison with DMSO in the bulk phase at 298 K. The local order of DMSO, analysed in terms of radial distribution functions is similar to that in the bulk except the case with the SWCNT (8, 8) where the anomalous structure pattern is realized. Meanwhile, the translational self-diffusion coefficients of DMSO in confinements are much lower then in the bulk phase (by a factor of 2–3) and correlate with a value of the SWCNT internal diameter. Using cylindrical distribution functions of DMSO atoms we elucidate that the slowdown of self-diffusion coefficient of DMSO confined in the SWCNTs is reduced by the first layer of DMSO molecules close to the SWCNT wall.     

Fabrication and electrochemical properties of free-standing single-walled carbon nanotube film electrodes

An easily manipulative approach was presented to fabricate electrodes using free-standing single-walled carbon nanotube (SWCNT) films grown directly by chemical vapor deposition.Electrochemical properties of the electrodes were investigated.In comparison with the post-deposited SWCNT papers,the directly grown SWCNT film electrodes manifested enhanced electrochemical properties and sensitivity of sensors as well as excellent electrocatalytic activities.A transition from macroelectrode to nanoelectrode behaviours was observed with the increase of scan rate.The heat treatment of the SWCNT film electrodes increased the current signals of electrochemical analyser and background current,because the heat-treatment of the SWCNTs in air could create more oxide defects on the walls of the SWCNTs and make the surfaces of SWCNTs more hydrophilic.The excellent electrochemical properties of the directly grown and heat-treated free-standing SWCNT film electrodes show the potentials in biological and electrocatalytic applications.     

Raman study of single wall carbon nanotube thin films treated by laser irradiation and dynamic and isothermal oxidation

The effect of visible and infrared irradiation on the structure of single wall carbon nanotubes (SWCNTs) is still an insufficiently resolved subject. In this paper, we report a detailed study of two types of SWCNT thin films treated by pulsed laser irradiation and dynamic and isothermal oxidation, respectively. Raman features of treated films were investigated by 532, 633 and 780 nm excitation lines, respectively. It was established that the 532 nm excitation laser line probes the surface of SWCNT films, while the two others probe the bulk of SWCNT films. It was found that during Raman measurements, one type of SWCNTs warms up significantly while the other type does not change temperature. Raman analysis of SWCNTs probed with 532 nm showed that effects of high power laser irradiation on two types of SWCNTs are completely different. Major effects are decomposition, debundlation and photooxidation. It was found that debundlation and removal of defective carbon are much more pronounced in one type of SWCNTs treated with dynamic oxidation. Dynamic oxidation affects mostly thinner SWCNTs that easily burn in air. The only significant effects of isothermal oxidation are the increase of defective amorphous carbon in the first type of SWCNTs and the decrease of D band and debundlation in the second type. Copyright © 2012 John Wiley & Sons, Ltd.     

空位结构缺陷对C纳米管弹性性质的影响

用分子动力学方法对不同空位缺陷的扶手椅型与锯齿型单壁C纳米管杨氏弹性模量进行了计算和分析. 结果表明：扶手椅型（5, 5）, （10,10）和锯齿型（9, 0）, （18, 0） 纳米管在无缺陷时其杨氏模量分别为948,901和804,860 GPa. 随管径的增大,扶手椅型和锯齿型单壁C纳米管弹性模量分别减小和增大,表现出完全不同的变化规律. 随着C纳米管中单点空位缺陷的均匀增加,杨氏模量下降,当缺陷比率增加到一定程度时,杨氏模量下降骤然趋缓,形成一下降平台;双空位缺陷对C纳米管杨氏模量的影响与其分布方向有关;随单点空位缺陷间原子数的增加,在轴向上,杨氏模量下降到某一值小幅波动,而在周向上杨氏模量先下降,然后上升到某一稳定值. 随两单点空位缺陷的空间距离进一步增大,杨氏模量又呈微降趋势. 通过分子间σ键与π键特征及缺陷间近程电子云耦合作用规律与空位缺陷内部5-1DB缺陷的形成特点等理论对上述规律进行了分析. 关键词： 空位缺陷 C纳米管 分子动力学 杨氏模量     

Anisotropic tight-binding model applied to zigzag ultra-small nanotubes

A single-wall carbon nanotube (SWCNT) can be visualized as a graphene rolled into a cylinder. Tight-binding band structure calculations, with hopping between nearest-neighbor π orbitals only (NNTB), established rules by which both the mode in which the graphene is rolled up and the diameter determine whether the SWCNT is a metal or a semiconductor. However, when the diameter of the SWCNT is ultra-small its large curvature results in the breakage of these rules. In this work, we studied zigzag (n, 0) SWCNTs with diameters smaller than 0.7 nm using a π orbital-only tight-binding model including anisotropy in the hopping between next-nearest-neighbor sites (ANNNTB). Band overlaps were found in the electronic band structures of the zigzag SWCNTs for n=3, 4, 5, and 6, indicating that they are metals. The reason why the band structures of armchair and chiral SWCNTs are less affected by curvature effects becomes clear with the ANNNTB model, as does the reason why non-degenerate states cause band overlaps of the zigzag SWCNTs for n=3, 4, 5, and 6. Our results show that a π orbital-only tight-binding model is able to describe both the band overlaps and gaps obtained by ab initio calculations for zigzag SWCNTs.     

Impact of Mo and Ce on growth of single-walled carbon nanotubes by chemical vapour deposition using MgO-supported Fe catalysts

A series of nine catalysts containing Ce/Fe and Mo/Fe at various loadings on MgO supports have been studied as catalysts for chemical vapour deposition (CVD) of single-walled carbon nanotubes (SWCNTs) using a methane carbon source. Our results show that the Ce/Fe system is very suitable as a catalyst that favours SWCNT growth, and we question the special importance that has been attributed to Mo as an additive to Fe-based catalysts for SWCNT growth, as it appears that Ce is equally effective. Our results indicate that dehydroaromatization (DHA) is not a defining step for the growth mechanism, as has been suggested for Mo/Fe systems previously, and show that Ce and Mo do not seriously perturb the well-known Fe/MgO system for growth of high quality SWCNT. Using Raman spectroscopy, we have shown that the Ce/Fe/MgO catalyst system favours growth of SWCNTs with a different distribution of chiralities compared to the analogous Mo/Fe/MgO system.     

低偏压下单层碳纳米管的输运特征

系统地计算了各种手性碳纳米管最低导带的电子速度和有效质量的变化规律,在此基础上推断手性碳纳米管低偏压下的输运特征,计算表明:在低偏压电子输运时,同一系列(手性角相同)的各种手性金属碳纳米管的输运性质相同,与管径无关,但不同系列的手性金属碳纳米管的输运性质有明显区别;而同一系列的各种手性半导体型碳纳米管的输运性质有一定差异,但不同系列的手性半导体型碳纳米管的输运性质有着显著差异.这一结果说明:碳纳米管在低偏压下的输运特征与系列有着密切的关系,手性角是决定各种碳纳米管在低偏压下具有不同输运性质的最关键的几何参 关键词： 碳纳米管 手性角 电子速度 有效质量