Micromechanical Behavior of Carbon Nanotube-Covered SiC Fibers in Polymer Matrix Composites

The incorporation of nanotube-covered fibers in continuous fiber/epoxy composites has been shown to influence the mechanical, electrical, and thermal properties of the composite. Increased interlaminar shear stress, flexural strength and modulus have been reported in such composites over composites containing bare fibers. In this study, the microstructure and interfacial shear strength (ISS) of continuous silicon carbide fiber/epoxy composites with and without nanotubes grown from the SiC fiber surface were investigated with micro-Raman spectroscopy (MRS) and microscopy. The fibers with nanotubes grown from the surface were found to have a reduced ISS compared with the bare fibers. Electron microscopy showed good wetting of epoxy in the nanotube forests, but poor attachment of the nanotube forests to the fibers. These results suggest that the mechanism leading to improvements in bulk composite properties is not due to an improvement in the fiber/matrix ISS.     

Reshaping elastic nanotubes via self-assembly of surface-adhesive nanoparticles

Elastic sheets with macroscopic dimensions are easy to deform by bending and stretching. Yet shaping nanometric sheets by mechanical manipulation is hard. Here we show that nanoparticle self-assembly could be used to this end. We demonstrate that spherical nanoparticles adhering to the outer surface of an elastic nanotube can self-assemble into linear structures: rings or helices on stretchable nanotubes, and axial strings on nanotubes with high rigidity to stretching. These self-assembled structures are inextricably linked to a variety of deformed nanotube profiles, which can be controlled by tuning the concentration of nanoparticles, the nanoparticle-nanotube diameter ratio and the elastic properties of the nanotube. Our results open the possibility of designing nanoparticle-laden tubular nanostructures with tailored shapes, for potential applications in materials science and nanomedicine.     

Carbon nanotubes: opportunities and challenges

Carbon nanotubes are graphene sheets rolled-up into cylinders with diameters as small as one nanometer. Extensive work carried out worldwide in recent years has revealed the intriguing electrical and mechanical properties of these novel molecular scale wires. It is now well established that carbon nanotubes are ideal model systems for studying the physics in one-dimensional solids and have significant potential as building blocks for various practical nanoscale devices. Nanotubes have been shown to be useful for miniaturized electronic, mechanical, electromechanical, chemical and scanning probe devices and materials for macroscopic composites. Progress in nanotube growth has facilitated the fundamental study and applications of nanotubes. Gaining control over challenging nanotube growth issues is critical to the future advancement of nanotube science and technology, and is being actively pursued by researchers.     

温度、应变率和空位缺陷对氮化硼纳米管压缩性能的影响

采用分子动力学方法,分别模拟了完好的和含有缺陷的氮化硼纳米管的轴向压缩过程。原子间的相互作用采用Tersoff多体势函数来描述。结果表明,同尺寸的锯齿型氮化硼纳米管的临界轴向压缩强度高于扶手型氮化硼纳米管,这与碳纳米管的研究结果一致。发现纳米管的压缩强度,如临界轴向内力在低温下受温度影响明显,并且和应变率的大小有关。然而,应变率对纳米管的弹性变形没有影响。另外,还发现空位缺陷降低了纳米管的力学性能。与完好的纳米管相比,含有缺陷的纳米管轴向压缩强度对于温度的影响并不敏感。     

First principles study of electronic structure and carrier mobility in β-armchair antimony nanotubes

In recent work, we have investigated the structure and stability of β-armchair antimony nanotubes (SbNT) using density functional theory (DFT). We studied electronic properties like electronic band structure, density of states (DOS) and mechanical properties such as stiffness constant, Poisson's ratio, and mechanical strength for these nanotubes. We found that these nanotubes are energetically stable and semiconducting in nature with band-gap varying between 1.32 eV to 1.47 eV. We have also calculated effective mass and carrier mobility for these nanotubes. Furthermore, stiffness constant and mechanical strength of these nanotubes increases with increase in diameter. While, $(4,4)$ nanotube shows anomalously higher strength than other nanotubes. The results of effective mass and carrier mobility for these nanotubes shows that electrons have higher effective mass and therefore lesser mobility than holes for most of the nanotubes. Our calculations show that β-armchair antimony nanotubes (SbNT) could be use in nano-electronics.     

The Effect of Small Additions of Carbon Nanotubes on the Mechanical Properties of Epoxy Polymers under Static and Dynamic Loads

The results of measurements of the mechanical characteristics of cured epoxy composites containing small and ultrasmall additions of single-walled carbon nanotubes in the concentration range from 0 to 0.133 wt % under static and dynamic loads are presented. Static measurements of strength characteristics have been carried out under standard test conditions. Measurements of the Hugoniot elastic limit and spall strength were performed under a shock wave loading of the samples at a deformation rate of (0.8–1.5) ß 10⁵ s^-1 before the fracture using explosive devices by recording and subsequent analyzing the evolution of the full wave profiles. It has been shown that agglomerates of nanotubes present in the structure of the composites after curing cause a significant scatter of the measured strength parameters, both in the static and in the dynamic test modes. However, the effects of carbon nanotube additions in the studied concentration interval on the physical and mechanical characteristics of the parameters were not revealed for both types of loading.     

Poly(Butylene Terephthalate)/Single Wall Carbon Nanotubes Composite Nanofibers by Electrospinning

Poly(buthylene terephthalate)(PBT)/single wall carbon nanotubes (SWCNTs) composite nanofibers were prepared by electrospinning. The effect of carbon nanotubes on the morphology, crystallization, and mechanical properties of the electrospun composite nanofibers were investigated by SEM, DSC, and tensile testing, respectively. SEM observations indicated that the presence of SWCNTs resulted in finer nanofibers for lower loading; however, a broader distribution, especially for the higher diameter ranges was found for nanofibers with higher amounts of carbon nanotubes. SWCNTs accelerated crystallization and acted as a nucleating agent; the degree of crystallinity increased with increasing content of SWCNTs, followed by a moderate decrease at higher content. Specific tensile strength and modulus of the PBT/SWCNTs composite nanofibers mats were higher than that of neat PBT nanofibers mat. However, the elongation at break of composite nanofibers mats was lower than that of the neat PBT nanofibers mat.     

Effect of uniaxial tensile strength on the electrical properties of doped carbon nanotubes: Density functional theory

We investigated the effect of uniaxial tensile strength on a pristine carbon nanotube, boron-doped carbon nanotube, nitrogen-doped carbon nanotube and co-doped carbon nanotube with boron and nitrogen atoms. To achieve our goal, we performed our calculations with the aid of density functional theory. We studied the changes in the electrical properties after the atomic substitution of a carbon atom by boron, nitrogen, and boron and nitrogen in pristine carbon nanotubes. We also applied uniaxial tensile strength to doped structures as well as pristine one. In addition to studying the band gap, we studied the changes in the Fermi energy, valence bands, and conduction bands. We found that defects as well as stress and strain play a crucial rule on modifying the electrical properties of carbon nanotubes.     

AFM detection of the mechanical resonances of coiled carbon nanotubes

We introduce a method for atomic force microscopy (AFM)-based detection of mechanical resonances in helix-shaped multi-walled carbon nanotubes. After deposition on an oxidized silicon substrate, the three-dimensional structure of suspended nanotubes, which bridges an artificially created step on the surface, can be visualized using AFM operating in the non-contact mode. The suspended coiled nanotubes are resonantly excited, in situ, at the fundamental frequency by an ultrasonic transducer connected to the substrate. When the AFM tip is positioned above the coiled nanotube, the cantilever is unable to follow the fast nanotube oscillations. Nevertheless, an oscillation amplitude-dependent signal is generated due to the non-linear force-to-distance dependence. Measurement of the mechanical resonances of the helix-shaped carbon nanotubes can be used to quantitatively determine their elastic properties. Assuming that a coiled nanotube can be modeled as a suspended helix-shaped uniformly thin elastic beam, the obtained resonance frequency is consistent with a Young's modulus of 0.17ǂ.05 TPa.     

Nanotube actuators for nanomechanics

Carbon nanotubes are unique nanostructures with interesting properties that suit them to a range of diverse applications including nanoscale electronics, use in composites, as gas storage media and scanning probe tips. An exciting property of carbon nanotubes is their ability to efficiently convert electrical energy into mechanical energy (actuation). Nanotube actuation is caused by the geometrical expansion of the carbon–carbon covalent bond caused by charge transfer into the nanotube [Abstract American Chemical Society 22 (1999); Abstract American Chemical Society 20 (2000)]. This ability to actuate, in addition to their high strength (∼1 TPa), makes macro-scale sheets of nanotubes termed `bucky paper', ideal for artificial muscles [Science 284 (1999) 1340]. Carbon nanotube actuators based on bucky paper have been shown to generate an order of magnitude higher stresses than those observed for natural muscle. These promising results suggest that carbon nanotube actuators based on a single (or a few hundred) nanotubes will also lead to enhanced applications on the micro- or nano-scale in the biomedical or electronic fields. This paper provides an overview of carbon nanotube actuators, their exceptional properties, current research ideas and possibilities for future applications.     

Review of two microwave applications of carbon nanotubes: nano-antennas and nano-switches

This paper provides an overview of two potential applications of carbon nanotube devices in microwave technology. Firstly, the main structural, mechanical, thermal and electronic properties of carbon nanotubes are briefly reviewed. Then, the possibilities offered by metallic carbon nanotubes as nano-antennas in the E- and W-bands and further are investigated: comparison with macroscopic wire antennas is made, the major advantages brought by nanotubes but also technical issues to be addressed are discussed. Finally, the integration of carbon nanotubes in nano-electro-mechanical-systems (NEMS) is studied through nano-switches: the contribution of carbon nanotubes is detailed, state-of-the-art is described, as well as our future approaches for such nano-devices. To cite this article: S. Demoustier et al., C. R. Physique 9 (2008).     

Transition from a Tomonaga-Luttinger liquid to a fermi liquid in potassium-intercalated bundles of single-wall carbon nanotubes

We report on the first direct observation of a transition from a Tomonaga-Luttinger liquid to a Fermi-liquid behavior in potassium-intercalated mats of single-wall carbon nanotubes. Using high resolution photoemission spectroscopy, an analysis of the spectral shape near the Fermi level reveals a Tomonaga-Luttinger liquid power law scaling in the density of states for the pristine sample and for low dopant concentration. As soon as the doping is high enough to achieve a filling of the conduction bands of the semiconducting tubes, a distinct transition to metallic single-wall carbon nanotube bundles with the scaling behavior of a normal Fermi liquid occurs.     

Exciton resonances quench the photoluminescence of zigzag carbon nanotubes

We show that the photoluminescence intensity of single-walled carbon nanotubes is much stronger in tubes with large chiral angles--armchair tubes--because exciton resonances make the luminescence of zigzag tubes intrinsically weak. This exciton-exciton resonance depends on the electronic structure of the tubes and is found more often in nanotubes of the +1 family. Armchair tubes do not necessarily grow preferentially with present growth techniques; they just have stronger luminescence. Our analysis allows us to normalize photoluminescence intensities and find the abundance of nanotube chiralities in macroscopic samples.     

Virtual Analyzers of Mat Quality Based on Slurry Sensors

Mats are often composites of fibers and filler particulates. They are formed by draining a dilute aqueous slurry on a filter medium called “forming fabric”, consolidated and dried. In general, formation of non-woven fibrous mats containing fibers and inorganic filler particulates is strongly influenced by the drainage characteristics of the slurry. These characteristics depend on chemical additives as well as physical properties of the slurry constituents — for example size distribution of fibers and fillers. The qualities of resulting mats, such as wet strength and water load, are important control parameters from the viewpoint of process runnability and efficiency. Proper control of mat quality parameters allows one to enhance productivity through scrap reduction. Using on-line slurry analyzer data in combination with the processing variables of the forming section, we can obtain estimates of mat quality parameters in real-time through applications of neural networks. We use neural networks to identify non-parametric functional approximations for predictive process modeling. This paper deals with real-time prediction of wet mat quality using on-line monitoring of slurry characteristics. This is significant as it allows one to obtain a product property that is normally available from destructive laboratory tests only.     

Nanoelectromechanical devices with carbon nanotubes

Thanks to their excellent mechanical properties as well as interesting electrical characteristics, carbon nanotubes are among the most widely used materials for the study of electromechanical properties. This review paper presents the physical properties and the potential applications of carbon nanotube based nanoelectromechanical devices. We present an overview of fabrication methods followed by a discussion of the physical properties of CNT-NEMS. Finally some potential applications are discussed.     

拉曼描述碳纳米管系统:缺陷探测,产物热处理,过程分析和催化剂(英文)

利用拉曼散射技术从多角度研究了碳纳米管合成系统。发现拉曼散射技术不仅可表征碳纳米材料本身的特性,而且可分析宏观的多壁碳纳米管与单壁碳纳米管的生长过程。针对不同的碳纳米材料的生长特性提出了催化剂与反应器设计及过程控制的研究方向。同时还发展了一种基于拉曼光谱法的定量测定单壁碳纳米管含量的方法。     

Some problems in understanding the electronic transport properties of carbon nanotube ropes

The resistance of single-wall carbon nanotube (SWCN) ropes or mats, and some individual tubes, typically shows a crossover from non-metallic to metallic temperature dependence as temperature increases. This systematic pattern is consistent with a series heterogeneous model involving metallic resistance and tunnelling through barriers such as defects and inter-rope contacts. The metallic resistivity term increases linearly with temperature for the ropes or mats, but faster for the individual nanotubes. In contrast to the almost vanishing thermoelectric power expected from electronic band structure calculations, the measured values for mats or films (including recent measurements in a vacuum) are even larger than for typical metals. The thermopower increases with temperature as for metals, but has a characteristic non-linear shape. This temperature dependence can be modelled, for example, with parallel conduction in metallic and semiconducting tubes, but the size of the metallic thermopower required is anomalously large.     

Vibrational analysis of double-walled carbon nanotubes with inner and outer nanotubes of different lengths

In this study, the Euler-Bernoulli beam model is used to analyze the resonant vibration of double-walled carbon nanotubes (DWCNTs) with inner and outer nanotubes of different lengths. The resonant properties of DWCNTs with different inner and outer nanotube lengths are investigated in detail using this theoretical approach. The resonant vibration is significantly affected by the vibrational modes of the DWCNTs, and by the lengths of the inner and outer nanotubes. For an inner or outer nanotube of constant length, the vibrational frequencies of the DWCNTs increase initially and then decrease as the length of another nanotube increases. A design for nanoelectromechanical devices that operate at various frequencies can be realized by controlling the length of the inner and outer nanotubes of DWCNTs. This investigation may be helpful in applications of carbon nanotubes such as high frequency oscillators, dynamic mechanical analysis and mechanical sensors.     

Mesoscopic thermal and thermoelectric measurements of individual carbon nanotubes

We discuss the mesoscopic experimental measurements of electron energy dissipation, phonon thermal transport, and thermoelectric phenomena in individual carbon nanotubes. The temperature distributions in electrically heated individual multiwalled carbon nanotubes have been measured with a scanning thermal microscope. The temperature profiles along the tube axis in nanotubes indicate the bulk dissipation of electronic energy to phonons. In addition, thermal conductivity of an individual multiwalled nanotube has been measured using a microfabricated suspended device. The observed thermal conductivity is two orders of magnitude higher than the estimation from previous experiments that used macroscopic mat samples. Finally, we present thermoelectric power (TEP) of individual single walled carbon nanotubes using a novel mesoscopic device. A strong modulation of TEP as a function of the gate electrode was observed.     

多层纳米碳管膜的大面积可控制生长

文章介绍了利用化学气相沉积法在Si和石英基片上大面积生长多层碳纳米管膜的研究成果,通过调节生长参数,不仅可以获得高度取向的碳纳米纤维,还可获得不同直径,不同图案的高度取向的碳纳米管膜,取向碳纳米管膜的可控制制备,为研究碳纳米管的物理,化学性能,特别是为碳纳米管场发射平面图像显示器的应用研究,奠定了坚实的基础。