Dispersion relation of dust acoustic waves in metallic multi-walled carbon nanotubes

In this paper,a charged multi-walled carbon nanotube(MWCNT),which is surrounded by charged nanoparticles,is modeled as a cylindrical shell of electron-ion-dust plasma.By employing classical electrodynamics formulations and the linearized hydrodynamic model,the dispersion relation of the dust acoustic wave oscillations in the composed system is investigated.We obtain a new low-frequency electrostatic excitation in the MWCNT,i.e.dust acoustic wave oscillations.     

Transverse elasticity of multi-walled carbon nanotubes

A discrete shell model is proposed to describe the radial deformation of carbon nanotubes under a hydrostatic pressure and the radial Young's modulus of (single- or multi-walled) nanotubes is obtained. It is found that the radial modulus decreases with increasing tube diameter while increases with increasing number of layers. The computational results agree well with the previous results of SWNTs and indicate that the radial modulus of carbon nanotubes is independent of the Poisson's ratio.     

XPS study of fluorinated carbon multi-walled nanotubes

Arc-produced carbon multi-walled nanotubes (MWNTs) were fluorinated at 420 °C in a flow of diluted F₂ gas containing small admixture of HF gas. Fluorinated materials (F-MWNTs) with 10–55 wt.% fluorine content were studied by XPS. It was shown that fluorination begins at the external layers of nanotubes and the reaction front propagates inside the multi-layer particles in concert with structural deterioration of graphene layers. The C₂F stoichiometry still allows MWNT wall integrity, similar to known for SWNTs. The fluorine contents in the product can noticeably exceed this higher fluorine limit for tube stability. The position of the F 1s line at 688.2 eV does not depend on the fluorine concentration. Nearly covalent C–F bonds dominate the F-MWNT samples, with a small quantity (2–9%) of ionic bonds also present. Fluorinated carbon tends to spatially separate from non-fluorinated carbon.     

Guided waves characteristics of multi-walled carbon nanotubes

The theoretical analysis of propagation of guided waves in the multi-walled carbon nanotubes is presented within the framework of the classical electrodynamics. Electronic excitations of each wall of the system are modeled as an infinitesimally thin cylindrical layer of the π-electrons, whose dynamics are described by means of the fluid theory. General expressions of dispersion relations are obtained for the electromagnetic wave with the transverse magnetic and transverse electric modes, respectively, by solving Maxwell and fluid equations with appropriate boundary conditions.     

多壁碳纳米管光限幅特性的研究

用化学气相沉积法制备了多壁碳纳米管,并将其溶解在甲苯溶液中.用波长为1064nm的皮秒脉冲激光测量该样品的透过率,发现了非常明显的光限幅特性.当入射光强较小时,透射光强度随入射光强度的增大而增大,输出与输入为线性关系;随着入射光强的增大,透射光强增长的速度明显变慢,并逐渐趋于饱和.当入射光强度较小时,样品的透过率接近100%;而当入射光强为8GW/cm²时,非线性透过率达到30%.根据三光子吸收理论计算,理论拟合与实验结果非常符合,说明多壁碳纳米管的三光子吸收产生了光限幅效应.实验测 关键词： 多壁碳纳米管 光限幅 三光子吸收     

Preparation and characterization of biocompatible magnetic carbon nanotubes

Magnetic carbon nanotubes consisting of multi-wall carbon nanotubes (MWNTs) core and Fe₃O₄ shell were successfully prepared by in situ thermal decomposition of Fe(acac)₃ or FeCl₃ or Fe(CO)₅ in 2-pyrrolidone containing acid treated MWNTs at 240 °C with the protection of nitrogen gas. The samples were characterized by TEM, XRD, SEAD, XPS and superconducting quantum interference device. Also, their biocompatibility was compared with naked carbon nanotubes. The results showed that after coated with Fe₃O₄ nanoparticles, the obtained magnetic carbon nanotubes show superparamagnetic characteristic at room temperature, and their blocking temperature is about 80 K. The magnetic properties of the nanotubes are relevant to the content of magnetic particles, increasing content of magnetic nanoparticles leads to higher blocking temperature and saturation magnetization. The results of antimicrobial activities to bacterial cells (Escherichia coli) showed that the MWNTs have antimicrobial activity, while the magnetic nanotubes are biocompatible even with a higher concentration than that of MWNTs.     

Nitrogen-doped multi-walled carbon nanotubes for paracetamol sensing

A novel sensor consisting of nitrogen-doped multi-walled carbon nanotubes was fabricated by means of chemical vapor deposition technique with decomposition of acetonitrile onto oxidized silicon wafer using ferrocene as catalyst. The electrochemical response of carbon nanotubes-based sensor towards oxidation of paracetamol to N-acetyl-p-quinone imine was investigated in phosphate buffer solution (pH 7.0) by means of standard electrochemical techniques. A quasi-reversible response for oxidation of paracetamol was identified on carbon nanotubes-based sensor with detection limit and sensitivity of 0.485 μM and 0.8406 A M^?1 cm^?2, respectively. It was found that the nitrogen doping in carbon nanotubes enhances the sensor's detection ability. Namely, electrochemical studies performed on film consisting of pristine carbon nanotubes reveal as well quasi-reversible response towards oxidation of paracetamol but nevertheless poorer detection ability and sensitivity (0.950 μM; 0.601 A M^?1 cm^?2). The findings strongly suggest the application of nitrogen-doped carbon nanotubes in biosensing.     

氢在多壁碳纳米管中的吸附储存

利用巨正则系综蒙特卡罗(GCMC)的方法模拟了氢在多壁碳纳米管中的吸附,氢气分子之间、氢气分子和碳原子之间的相互作用势能采用Lennard-Jones势能模型。模拟了不同结构参数(管内径、管壁数、管壁间距)的多壁碳纳米管在77K和298K下的吸附等温线,分析了多壁碳纳米管的管内径、管壁数以及管壁间距对吸附性能的影响。模拟结果表明:多壁碳纳米管的管壁数和管壁间距对吸附性能的影响较明显;管壁数越少,管壁间距越大,其吸附性能越好;多壁碳纳米管的管内径对其吸附性能的影响甚微。     

Milling and dispersion of multi-walled carbon nanotubes in texanol

Rheological results were used to determine the optimum type of dispersant and its concentration for six commercial dispersants for the dispersion of multi-walled carbon nanotube (MWCNT) agglomerates in texanol. An unsaturated polycarboxylic acid copolymer (BYK P-104) exhibited the optimum performance with the lowest MWCNT slurry viscosity in texanol. The cutting and dispersion efficiencies of MWCNTs with 20 wt.% of BYK P-104 dispersant were compared using conventional ball milling and high energy milling, whereby the latter was found to be more effective. High energy milling for 2 h produced a large portion of MWCNT agglomerates smaller than 150 nm, showing a drastic increase in slurry viscosity due to the dispersion into individual CNTs. On the other hand, 120 h ball milling was required to achieve the agglomerate size of 300 nm with less viscosity increase upon milling. Decrease in the degree of MWCNT crystallinity was observed by both milling, even though 2 h high energy milling showed slightly less damage than 120 h ball milling based on XRD and Raman spectroscopy results.     

Preparation and characterization of amphiphilic multi-walled carbon nanotubes

Multiwalled carbon nanotubes (MWCNTs, average diameter 8 nm) functionalized by N-vinyl pyrrolidone (NVP) were synthesized by radical polymerization and characterized by Fourier transform infrared and Raman spectroscopies, thermogravimetric analysis and transmission electron microscopy. These NVP–MWCNTs exhibit remarkable solubility in water, ethanol and dimethyl formamide. The polyvinyl pyrrolidone can be attached onto the surface of the MWCNTs and the degree of functionalization is affected by NVP content. The functionalization causes possible grafting reaction and solid physical coating between MWCNTs and PVP.     

Low voltage STEM imaging of multi-walled carbon nanotubes

We present high magnification STEM images of multi-walled carbon nanotubes recorded with a 5 keV electron beam using a Helios Dual Beam microscope and a dedicated multi-segment transmission (STEM) detector. Images of carbon nanotubes recorded with bright-field (BF), annular dark-field (ADF) and high angle annular dark-field (HAADF) signals all show high contrast features, with internal structures 1-2 nm in width clearly revealed in the STEM images. Thicker regions of the nanotubes appear to show an unusual contrast reversal when comparing ADF and HAADF images. An understanding of the image contrast, and its dependence on thickness, is obtained by computing simulations of the ADF and HAADF images using Monte-Carlo software taking into account electron scattering in the nanotube.     

Covalent functionalization of multi-walled carbon nanotubes by lipase

Lipase from Candida rugosa was covalently anchored onto acid-treated multi-walled carbon nanotubes (MWNTs) through a self-catalytic mechanism. A variety of characterization techniques including FTIR, Raman spectroscopy, and XPS were employed to demonstrate the formation of the ester linkage between lipase and MWNTs. The MWNTs-lipase biocomposites showed significantly increased solubility in some common-used organic solvents, such as THF, DMF and chloroform. This study may offer a novel and facile route for covalent modification of carbon nanotubes, and expand the potential utilization of both lipases and MWNTs in the fields of biocatalyst and biosensor.     

Field electron emission images of multi-walled carbon nanotubes

Field electron emission microscope images from multi-walled carbon nanotubes can typically be characterized by the presence of five pentagons surrounding a sixth central pentagon. The observations of bright line centered interference patterns between adjacent pentagons in the field electron emission microscope images of multi-walled carbon nanotubes have been reported in the literature. We have observed a shift from bright to dark line centered interference patterns and associated this with the presence of surface adsorption. In order to identify the origin of the contaminant, multi-walled carbon nanotubes were dosed with H₂, H₂O, CO and O₂ and then imaged in the field electron emission microscope. Only the samples exposed to O₂ showed a shift from a bright line centered pattern between adjacent pentagons of a clean surface to a dark line centered pattern when one pentagon was contaminated or a bright line centered pattern when both adjacent pentagons become contaminated. The results of the experimental studies and the modeling of the changes in the field emission pattern as phase shifts in the wave function of the tunneling electrons due to modifications in the surface work function are presented.     

Dispersion and alignment of carbon nanotubes in polycarbonate

Dispersion and alignment of carbon nanotubes in thermoplastic polymers such as polycarbonate have been studied. Dispersion was accomplished by mixing in a conical twin-screw extruder and alignment was carried out using a fiber-spinning apparatus. The effects of mixing time and fiber draw rates on dispersion and alignment were investigated. Uniform dispersions were produced with relatively short residence times in the extruder. Excellent alignment of carbon nanotubes in nanocomposite filaments was obtained when the fiber draw rate was greater than 70 m/min. The ability to closely control the dispersion and alignment of carbon nanotubes in polymers is expected to lead to the development of nanocomposites with desirable electronic and structural properties. Received: 7 January 2002 / Accepted: 11 April 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +1-508/233-5521, E-mail: Michael.Sennett@natick.army.mil     

Temperature enhanced growth of ultralong multi-walled carbon nanotubes forest

This work demonstrates a method to synthesize ultralong multi-walled carbon nanotubes (MW-CNTs) forest with high growth rate using the three-zone temperature chemical vapor deposition (TZT-CVD). The effect of temperature difference in the TZT-CVD is to sustain the lifetime of the catalyst and hence increase the growth efficiency. By optimizing the growth variables, TZT-CVD produced MW-CNTs forest with a height up to 4.27 mm in 60 min. The CNT synthesis ratio, an ultimate figure of merit is 712 times and the carbon source consumption is 4% compared to that of single-zone temperature CVD.     

Radial buckling of multi-walled carbon nanotubes under hydrostatic pressure

Radial buckling stresses of carbon nanotubes (CNTs) need to be studied in high-pressure resonance Raman scattering spectrum. In this work, the closed-form expression of the critical buckling stress of multi-walled carbon nanotubes (MWCNTs) under hydrostatic pressure is derived that can be conveniently employed. Using the derived formulae, the critical buckling stresses of single-walled carbon nanotubes and double-walled carbon nanotubes with different diameters are calculated. The results are in good agreement with other reported literatures. In addition, the critical buckling stresses of each layer of a quintuple-walled CNT in different buckling modes are predicted, showing that the buckling instability can occur not only in the outermost rolled layer, but also in other rolled layer of MWCNTs by considering different diameters and buckling modes.     

Effect of different microwave-based treatments on multi-walled carbon nanotubes

Three new methods for the functionalization of multi-walled carbon nanotubes (MWCNTs) are reported using microwave (MW) energy and water as a mild chemical agent. In the first method we reported the effect of MW irradiation on a dispersion of MWCNTs in deionized water, in the second method we studied the exposing of MWCNT to microwave irradiation in the presence of steam, and in the third method we used microwave oven-generated plasma for the functionalization of MWCNTs. We also performed thermal oxidation and acid treatment as two conventional methods for oxidative functionalization of carbon nanotubes, to compare their effect with our results. Transmission electron microscopy (TEM) and Raman spectroscopy results showed that although these microwave methods introduced some defects to the carbon nanotubes, the damage was less severe than conventional treatments. X-ray photoelectron spectroscopy (XPS) measurements confirmed that the functionalization of carbon nanotubes by these methods favored hydroxyl groups, which are useful when further functionalization is required.     

不同参数多壁碳纳米管太赫兹谱特性

探索不同管径和长度的多壁碳纳米管（MWCNT）的太赫兹（THz）谱特性,采用透射型太赫兹时域光谱系统研究了5个不同管径和长度的MWCNT样品的太赫兹吸收谱和折射率谱,并对比和分析了它们的差异。结果表明：在0.2～2.0 THz内,多壁碳纳米管太赫兹吸收没有特征吸收峰,吸收强度随着频率的增加而增加,并可以拟合为不同斜率的直线,且MWCNT在THz波段的吸收强度与管径和长度成正比。折射率随着频率的增加呈指数衰减,同时,管径是影响其折射率的一个重要因素,而长度对其影响不大。     

不同参数多壁碳纳米管太赫兹谱特性

探索不同管径和长度的多壁碳纳米管(MWCNT)的太赫兹(THz)谱特性,采用透射型太赫兹时域光谱系统研究了5个不同管径和长度的MWCNT样品的太赫兹吸收谱和折射率谱,并对比和分析了它们的差异。结果表明:在0.2~2.0THz内,多壁碳纳米管太赫兹吸收没有特征吸收峰,吸收强度随着频率的增加而增加,并可以拟合为不同斜率的直线,且MWCNT在THz波段的吸收强度与管径和长度成正比。折射率随着频率的增加呈指数衰减,同时,管径是影响其折射率的一个重要因素,而长度对其影响不大。