Vibration analysis of single-walled carbon nanotubes using different gradient elasticity theories

The present work aims at investigating the vibrational characteristics of single-walled carbon nanotubes (SWCNTs) based on the gradient elasticity theories. The small-size effect, which plays an essential role in the dynamical behavior of nanotubes, is captured by applying different gradient elasticity theories including stress, strain and combined strain/inertia ones. The theoretical formulations are established based upon both the Euler–Bernoulli and the Timoshenko beam theories. To validate the accuracy of the present analysis, molecular dynamics (MDs) simulations are also conducted for an armchair SWCNTs with different aspect ratios. Comparisons are made between the aforementioned different gradient theories as well as different beam assumptions in predicting the free vibration response. It is shown that implementation of the strain gradient elasticity by incorporating inertia gradients yields more reliable results especially for shorter length SWCNTs on account of two small scale factors corresponding to the inertia and strain gradients. Also, the difference between two beam models is more prominent for low aspect ratios and the Timoshenko beam model demonstrates a closer agreement with MD results.     

Nanodispersion of single-walled carbon nanotubes using dichloroethane

In this paper we present a simple approach of nanodispersing single-walled carbon nanotubes (SWCNTs) in a non-polar 1,2-dichloroethane (DCE) solvent. After filtration with isopropanol and acetone, the purified SWCNTs were immersed in DCE, followed by sonication for about 15 hours. The samples were further centrifuged at 17,000 revolutions per minute for about 3 hours. Atomic force microscopy (AFM) demonstrated that the spin-coated nanotubes were mostly individual nanotubes with an average diameter of 1.6 nm and a length of about 250 nm. We also found that the presence of water, and the dry process during DCE treatment, prevented nanotubes from being nanodispersed.     

Mitochondria-targeting photoacoustic therapy using single-walled carbon nanotubes

In vitro photoacoustic therapy using modified single-walled carbon nanotubes (SWNTs) as "bomb" agents is a newly reported approach for cancer. Herein, a mitochondria-targeting photoacoustic modality using unmodified SWNTs and its in vitro and in vivo antitumor effect are reported. Unmodified SWNTs can be taken up into cancer cells due to a higher mitochondrial transmembrane potential in cancerous cells than normal cells. Under the irradiation of a 1064 nm pulse laser, 79.4% of cancer cells with intracellular SWNTs die within 20 s, while 82.3% of normal cells without SWNTs remain alive. This modality kills cancer cells mainly by triggering cell apoptosis that initiates from mitochondrial damage, through the depolarization of mitochondria and the subsequent release of cytochrome c after photoacoustic therapy. It is very effective in suppressing tumor growth by selectively destroying tumor tissue without causing epidermis injury. Taken together, these discoveries provide a new method using mitochondria-localized SWNTs as photoacoustic transducers for cancer treatment.     

Temperature sensing using individual single-walled carbon nanotubes

Molecular dynamics simulations and quantum transport theory are employed to study the temperature-dependent electrical properties of individual (12,0) zigzag and (5,5) armchair carbon nanotubes deposited on silicon substrates. The results demonstrate that the magnitude of the leakage current depends on the length of the nanotube. Furthermore, the leakage current is generated periodically along the length of the nanotube. Finally, the results indicate that given an appropriate value of the applied bias voltage, the induced current varies linearly with the temperature over specific temperature ranges. As a result, the temperature can be inversely derived from the measured current signal. Overall, the results show that the (12,0) zigzag and (5,5) armchair carbon nanotubes are suitable for temperature sensing applications over temperature ranges of 200-420?K and 300-440?K, respectively.     

Tunable separation of single-walled carbon nanotubes by dual-surfactant density gradient ultracentrifugation

We present a systematic study of the effects of surfactants in the separation of single-walled carbon nanotubes (SWNTs) by density gradient ultracentrifugation (DGU). Through analysis of the buoyant densities, layer positions, and optical absorbance spectra of SWNT separation using the bile salt sodium deoxycholate (DOC) and the anionic salt sodium dodecyl sulfate (SDS), we clarify the roles and interactions of these two surfactants in yielding different DGU outcomes. The separation mechanism described here can also help in designing new DGU experiments by qualitatively predicting outcomes of different starting recipes, improving the efficacy of DGU and simplifying post-DGU fractionation.      

Torsional vibration analysis of double walled carbon nanotubes using nonlocal elasticity

In the present study, the torsional vibration behavior of double walled carbon nanotubes (DWCNTs) is investigated using nonlocal elasticity theory. The effects of van der Waals Force interaction, nanotube length and nonlocal parameter are studied in detail. Two frequency set are obtained for DWCNTs for a given half wave number. It is also shown that some mode shapes are anti-phase and some of them are in-phase. The present results can be useful in design of nano electromechanical systems like nanobearings and rotary servomotors.     

Cutting single-walled carbon nanotubes

A two-step process is utilized for cutting single-walled carbon nanotubes (SWNTs). The first step requires the breakage of carbon-carbon bonds in the lattice while the second step is aimed at etching at these damage sites to create short, cut nanotubes. To achieve monodisperse lengths from any cutting strategy requires control of both steps. Room-temperature piranha and ammonium persulfate solutions have shown the ability to exploit the damage sites and etch SWNTs in a controlled manner. Despite the aggressive nature of these oxidizing solutions, the etch rate for SWNTs is relatively slow and almost no new sidewall damage is introduced. Carbon-carbon bond breakage can be introduced through fluorination to ～C(2)F, and subsequent etching using piranha solutions has been shown to be very effective in cutting nanotubes. The final average length of the nanotubes is approximately?100?nm with carbon yields as high as 70-80%.     

Free vibration analysis of carbon nanotubes by using three-dimensional theory of elasticity

This paper studies vibration behavior of single-walled carbon nanotubes based on three-dimensional theory of elasticity. To accounting for the size effect of carbon nanotubes, nonlocal theory is adopted to the shell model. The nonlocal parameter is incorporated into all constitutive equations in three dimensions. Governing differential equations of motion are reduced to the ordinary differential equations in thickness direction by using Fourier series expansion in axial and circumferential direction. The state equations obtained from constitutive relations and governing equations are solved analytically by making use of the state space method. A detailed parametric study is carried out to show the influences of the nonlocal parameter, thickness-to-radius ratio and length-to-radius ratio. Results reveal that excluding small-scale effects caused decreasing accuracy of natural frequencies. Furthermore, the obtained closed form solution can be used to assess the accuracy of conventional two-dimensional theories.     

用气相流动催化热解法合成单壁碳纳米管

以正硅酸乙酯(TEOS)为前驱体，二茂铁为催化剂前驱体，利用气相流动催化热解法在850～1160℃连续合成了单壁碳纳米管(SWNTs)．在此过程中，以由TEOS分解得到的二氧化硅颗粒和二茂铁分解得到的铁颗粒在气流中直接形成的复合粒于作为催化剂，二氧化硅作为铁颗粒的载体．电于显微镜和激光拉曼光谱的观测和分析表明，在所得到的产物中SWNTs的含量约为10％，其直径为1～2nm。     

Formylation of single-walled carbon nanotubes

We report an improved, elegant method for the covalent formylation of single-wall carbon nanotubes (SWNTs) via formyl transfer from N-formylpiperidine, which could potentially open the gateway for more versatile chemical modification of carbon nanotube (CNT) walls than is possible via other reported functionalisation methods. The formylation reaction does not inflict damage upon the pristine CNT structure, unlike the currently commonly used carboxylation route, and involves much fewer steps, and takes considerably less time, than most other reported routes. The modified SWNTs have been characterised by Raman spectroscopy, ultraviolet-visible-near infrared (UV-vis-NIR) spectroscopy and "covalent tagging" with derivatising groups followed by thermogravimetric analysis-mass spectroscopy (TGA-MS). UV-vis-NIR spectroscopy shows that there is only limited disruption of the intrinsic electronic structure of the SWNTs. This is confirmed from estimates of the extent of functionalisation from TGA-MS, which suggest that it may be as low as 2 atomic per cent.     

Purification of single-walled carbon nanotubes

The discovery of carbon nanotubes (CNTs) created much excitement and stimulated extensive research into the properties of nanometer-scale cylindrical networks. From then on, various methods for the synthesis and characterization of aligned CNTs-both single-walled (SWCNTs) and multi-walled (MWCNTs) by different methods have been hotly pursued. Unfortunately, most methods currently in use produce raw multi component solid products, only a small fraction of which contains carbon nanotubes. The balance of the material is composed of residual catalyst particles (some of which are encased in concentric graphitic shells), fullerenes, other graphitic materials and amorphous carbon. These impurities cause a serious impediment for their detailed characterization and applications. If the carbon nanotube is ever to fulfill its promise as an engineering material, large, high quality aliquots will be required. A number of purification methods involving elimination processes such as physical separation, gas phase and liquid phase oxidation in combination with chemical treatments have been developed for nanotube materials. Though the quantitative determination of purity remains controversial, reported yields are best regarded with an appropriate level of skepticism on the method of assay. In this article, a review is given on the past and recent advances in purification of SWCNTs.     

FTIR and thermogravimetric analysis of biotin-functionalized single-walled carbon nanotubes

We report the covalent functionalization of single-walled carbon nanotubes (SWNTs) with biotin. The synthesized functionalized SWNT materials were fully characterized by FTIR and thermogravimetric analysis. These characterization techniques provided valuable information concerning the nature of the obtained SWNT materials as well as the efficiency of the employed synthetic route towards SWNT covalent functionalization with biotin.     

基于非局部应变梯度欧拉梁模型的充流单壁碳纳米管波动分析

将非局部弹性理论和应变梯度理论结合,再根据流体滑移边界理论,建立了考虑流体和固体小尺度效应的充流单壁碳纳米管(SWCNT)流固耦合动力学模型,分别以非局部应力效应、应变梯度效应和流体滑移边界效应模拟微观小尺度效应对系统的影响,推导得出充流单壁碳纳米管的Euler-Bernoulli梁波动控制方程。通过对控制方程的求解,分析材料不同类型尺度效应对充流碳纳米管的振动和波动特性影响。结果显示,应变梯度效应和流体边界效应对低频波动起促进作用,对高频波动起阻尼作用,应力非局部效应则对波动始终产生阻尼作用。三种尺度效应对低流速系统的振动有促进作用,而对高流速系统产生阻尼作用。     

Three dimensional single-walled carbon nanotubes

We report a simple fabrication method of creating a three-dimensional single-walled carbon nanotube (CNT) architecture in which suspended CNTs are aligned parallel to each other along the conventionally unused third dimension at lithographically defined locations. Combining top-down lithography with the bottom-up block copolymer self-assembly technique and utilizing the excellent film forming capability of polymeric materials, highly uniform catalyst nanoparticles with an average size of 2.0 nm have been deposited on sidewalls for generating CNTs with 1 nm diameter. This three-dimensional platform is useful for fundamental studies as well as technological exploration. The fabrication method described herein is applicable for the synthesis of other very small 1D nanomaterials using the catalytic vapor deposition technique.     

Optically active single-walled carbon nanotubes

The optical, electrical and mechanical properties of single-walled carbon nanotubes (SWNTs) are largely determined by their structures, and bulk availability of uniform materials is vital for extending their technological applications. Since they were first prepared, much effort has been directed toward selective synthesis and separation of SWNTs with specific structures. As-prepared samples of chiral SWNTs contain equal amounts of left- and right-handed helical structures, but little attention has been paid to the separation of these non-superimposable mirror image forms, known as optical isomers. Here, we show that optically active SWNT samples can be obtained by preferentially extracting either right- or left-handed SWNTs from a commercial sample. Chiral 'gable-type' diporphyrin molecules bind with different affinities to the left- and right-handed helical nanotube isomers to form complexes with unequal stabilities that can be readily separated. Significantly, the diporphyrins can be liberated from the complexes afterwards, to provide optically enriched SWNTs.     

Highly selective dispersion of single-walled carbon nanotubes using aromatic polymers

Solubilizing and purifying carbon nanotubes remains one of the foremost technological hurdles in their investigation and application. We report a dramatic improvement in the preparation of single-walled carbon nanotube solutions based on the ability of specific aromatic polymers to efficiently disperse certain nanotube species with a high degree of selectivity. Evidence of this is provided by optical absorbance and photoluminescence excitation spectra, which show suspensions corresponding to up to approximately 60% relative concentration of a single species of isolated nanotubes with fluorescence quantum yields of up to 1.5%. Different polymers show the ability to discriminate between nanotube species in terms of either diameter or chiral angle. Modelling suggests that rigid-backbone polymers form ordered molecular structures surrounding the nanotubes with n-fold symmetry determined by the tube diameter.     

单壁碳纳米管束的排布

流体排布法是实现碳纳米管定向排列的一种简单的方法。采用流体排布法在具有浸润性图案化的基底上成功地对单壁碳纳米管(SWNTs)束进行了水平方向上的排布。将SWNTs悬浮液滴入光刻胶制成的微通道中,在流体剪切力作用下,弯曲的SWNTs在一定程度上会被拉伸并且平行地排列在纳米级宽度的微通道中。将排列好的SWNTs阵列转移到一些不同间距的金电极对上面,制作成碳纳米管场效应晶体管(CNTFET)。CNTFET的电性能测试结果表明,制备的SWNTs束可以制造出不同电极间距同时具有良好电性能的CNTFET。     

Band theory of single-walled carbon nanotubes

In this paper, a curvilinear coordinate system is used in space and in k-space to study the energy band of single-walled carbon nanotubes wrapped at a helical angle. Using this method, a general function of the bandgap associated with the radius of the tube and the helical angle is derived based on the tight-binding theory. The three-dimensional hexagonal Brillouin zone of the tube is on the surface of cylinder in the k-space. For two tubes with different diameters, there is a distance between the cylindrical Brillouin zones in the radial direction. The Brillouin zone varies with the radius of the tube and the number of cells on the circumference. For the metallic zigzag tubes, the bandgaps decrease discretely to zero at the corners of the Brillouin zones, and those corners are singular points of zero gaps. With the transformation of coordinates, the metallic zigzag type is proven to be equivalent to an armchair configuration. Electrical characteristics of the chiral effects are briefly highlighted.     

Length-dependent extraction of single-walled carbon nanotubes

A two-phase liquid-liquid extraction process is presented which is capable of extracting water-soluble single-walled carbon nanotubes into an organic phase. The extraction utilizes electrostatic interactions between a common phase transfer agent and the sidewall functional groups on the nanotubes. Large length-dependent van der Waals forces for nanotubes allow the ability to control the length of nanotubes extracted into the organic phase as demonstrated by atomic force microscopy.