Carbon nanotubes are believed to be the ultimate low-density high-modulus fibers, which makes their characterization at nanometer scale vital for applications. By using an atomic force microscope and a special substrate, the elastic and shear moduli of individual single-walled nanotube (SWNT) ropes were measured to be of the order of 1 TPa and 1 GPa, respectively. In contrast to multiwalled nanotubes, an unexpectedly low intertube shear stiffness dominated the flexural behavior of the SWNT ropes. This suggests that intertube cohesion should be improved for applications of SWNT ropes in high-performance composite materials. [S0031-9007(98)

A variety of outstanding experimental results on the elucidation of the elastic properties of carbon nanotubes are fast appearing. These are based mainly on the techniques of high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) to determine the Young's moduli of single-wall nanotube bundles and multi-walled nanotubes, prepared by a number of methods. These results are confirming the theoretical predictions that carbon nanotubes have high strength plus extraordinary flexibility and resilience. As well as summarising the most notable achievements of theory and experiment in the last few years, this paper explains the properties of nanotubes in the wider context of materials science and highlights the contribution of our research group in this rapidly expanding field. A deeper understanding of the relationship between the structural order of the nanotubes and their mechanical properties will be necessary for the development of carbon-nanotube-based composites. Our research to date illustrates a qualitative relationship between the Young's modulus of a nanotube and the amount of disorder in the atomic structure of the walls. Other exciting results indicate that composites will benefit from the exceptional mechanical properties of carbon nanotubes, but that the major outstanding problem of load transfer efficiency must be overcome before suitable engineering materials can be produced. PACS: 62.20.x; 62.20.Dc; 61.48.+c; 61.16.Ch; 61.16.ByRolling up a graphene sheet on a nanometre scale [1] has dramatic consequences on the electrical properties [2]. The small diameter of a carbon nanotube (CNT) also has an important effect on the mechanical properties, compared with traditional micron-size graphitic fibres [3]. Perhaps the most striking effect is the opportunity to associate high flexibility and high strength with high stiffness, a property that is absent in graphite fibres. These properties of CNTs open the way for a new generation of high performance composites. Theoretical studies on the mechanical properties of CNTs * Corresponding author are more numerous and more advanced than experimental measurements, mainly due to the technological challenges involved in the production of nanotubes and in the manipulation of nanometre-sized objects. However, recent developments in instrumentation (particularly high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM)), production, processing and manipulation techniques for CNTs, have given remarkable experimental results. In this review, we cover different aspects of the mechanical properties of nanotubes and nanotube-based composites referring to theoretical and experimental work of different groups. We do not aim to be exhaustive, but prefer to focus on what we believe to be the most significant results.The mechanical properties are strongly dependent on the structure of the nanotubes. This is due to the high anisotropy of graphite. In our laboratory, three kinds of nanotubes have been studied: bundles of ...

During their production, single-walled carbon nanotubes form bundles. Owing to the weak van der Waals interaction that holds them together in the bundle, the tubes can easily slide on each other, resulting in a shear modulus comparable to that of graphite. This low shear modulus is also a major obstacle in the fabrication of macroscopic fibres composed of carbon nanotubes. Here, we have introduced stable links between neighbouring carbon nanotubes within bundles, using moderate electron-beam irradiation inside a transmission electron microscope. Concurrent measurements of the mechanical properties using an atomic force microscope show a 30-fold increase of the bending modulus, due to the formation of stable crosslinks that effectively eliminate sliding between the nanotubes. Crosslinks were modelled using first-principles calculations, showing that interstitial carbon atoms formed during irradiation in addition to carboxyl groups, can independently lead to bridge formation between neighbouring nanotubes.

We have determined the mechanical anisotropy of a single microtubule by simultaneously measuring the Young's and the shear moduli in vitro. This was achieved by elastically deforming the microtubule deposited on a substrate tailored by electron-beam lithography with a tip of an atomic force microscope. The shear modulus is 2 orders of magnitude lower than the Young's, giving rise to a length-dependent flexural rigidity of microtubules. The temperature dependence of the microtubule's bending stiffness in the 5-40 C range shows a strong variation upon cooling coming from the increasing interaction between the protofilaments. DOI: 10.1103/PhysRevLett.89.248101 PACS numbers: 87.16.Ka, 81.07.-b, 81.70.Bt, 87.15.La Microtubules are a filamentous assembly of protein subunits, -and -tubulin. They are hollow cylinders with external and internal diameters of 25 nm and 15 nm, respectively [1]. Along with actin and intermediate filaments, they form the eukaryotic cytoskeleton and participate in defining cell morphology. They also perform various vital functions unique to them: they act as building blocks for cilia and flagella and as tracks along which molecular motors move. These roles are determined by their structure and mechanical properties.The complex dynamics of microtubules (MTs) and other cytoskeletal elements play a key role in cell division, motility, and determination of cell shape. Their elastic properties and interaction with the cell membrane are crucial in understanding cell morphology. Quantifying the mechanical properties of microtubules is also necessary for explaining the elasticity of, for example, sensory hair cells and sperm tails. Influence of various physical conditions such as temperature or chemical agents, for example, drugs, could also be better understood by precisely measuring the mechanical response of an MT, governed by Young's (tensile stiffness) and shear modulus. Conventional studies involving atomic force microscopy (AFM) demand a specific biochemical functionalization of the supporting surface, the sample, and the force-exerting tool, the AFM tip, in order to transmit a stretching load to biomolecules [2]. Although these methods work remarkably well for studying the stretchiness of single molecules (DNA, proteins, etc.), they do not give a complete description of complex systems like MTs, which are a loosely connected assembly of protofilaments. In such biomaterials, not only the properties of the individual components, but also the interactions between them -lateral as well as longitudinal -reflected in the elastic properties, play an important role. Here we report for the first time the elastic moduli of MTs stabilized in vitro, using a new approach for measuring mechanical properties of complex biological systems. This method gives both shear and Young's moduli, and demonstrates the high mechanical anisotropy of MT structure.Previously performed experiments on mechanical properties of microtubules reported in the literature (with the exception of the only result obtained using AF...

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