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T W Chou - One of the best experts on this subject based on the ideXlab platform.
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Failure of carbon nanotube/polymer composites and the effect of nanotube waviness
Composites Part A-applied Science and Manufacturing, 2009Co-Authors: Chunyu Li, T W ChouAbstract:This paper studies the failure of CNT/polymer composites by combining micromechanics model and finite element simulation. A computational model of composite of adequate size is employed so the interactions between Nanotubes embedded in the matrix can be taken into account. The effects of nanotube waviness and random nanotube distribution relative to aligned straight Nanotubes are investigated. The computational results indicate that the nanotube waviness tend to reduce the elastic modulus but increase the ultimate strain of a composite. The randomness of nanotube distribution tends to reduce both the composite elastic modulus and tensile strength. The damage initiation and evolution in composites with random wavy Nanotubes have also been analyzed.
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Electrical conductivities of composites with aligned carbon Nanotubes.
Journal of nanoscience and nanotechnology, 2009Co-Authors: Chia Hung Li, T W ChouAbstract:This paper reports an analysis of the effect of nanotube alignment on the electrical conductivity of carbon nanotube-based composites using a percolation model. Both straight and wavy Nanotubes are considered. The thickness of an insulating matrix film between crossing Nanotubes is randomly selected in the range of 0-1.8 nm and the resulting contact resistance is correspondingly determined based on the Simmon's formula. Results of Monte Carlo simulations indicate that the electrical conductivity of composites with aligned Nanotubes is either lower or higher than that of composites with random nanotube orientation, depending on the degree of alignment and for wavy Nanotubes the highest conductivity occurs when nanotube are slightly aligned. The anisotropy of conductivity is also found strongly affected by nanotube alignment especially when the nanotube contents are small. The findings reached in this study coincide with some experimental observations on carbon nanotube-based composites.
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Effect of nanotube waviness on the electrical conductivity of carbon nanotube-based composites
Composites Science and Technology, 2008Co-Authors: Chunyu Li, Erik T. Thostenson, T W ChouAbstract:Abstract This paper reports the effect of nanotube waviness on the electrical conductivity of carbon nanotube-based composites using a percolation model. Wavy Nanotubes are approximated by elongated polygons, and the current-carrying backbones of percolation clusters in the composite are identified by the direct electrifying algorithm. The tunneling resistance due to an insulating film of matrix material between crossing Nanotubes is considered. Results of Monte Carlo simulations indicate that the electrical conductivity of composites with wavy Nanotubes are lower than that of composites with straight Nanotubes. The critical exponent of the power-law dependence of electrical conductivity on nanotube concentration decreases with increasing nanotube curl ratio. The conductivity exhibits an inverse power-law dependence on the curl ratio with a critical exponent in the range of 2.2–2.6.
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Effect of nanotube waviness on the electrical conductivity of carbon nanotube-based composites
Composites Science and Technology, 2008Co-Authors: Chunyu Li, Erik T. Thostenson, T W ChouAbstract:This paper reports the effect of nanotube waviness on the electrical conductivity of carbon nanotube-based composites using a percolation model. Wavy Nanotubes are approximated by elongated polygons, and the current-carrying backbones of percolation clusters in the composite are identified by the direct electrifying algorithm. The tunneling resistance due to an insulating film of matrix material between crossing Nanotubes is considered. Results of Monte Carlo simulations indicate that the electrical conductivity of composites with wavy Nanotubes are lower than that of composites with straight Nanotubes. The critical exponent of the power-law dependence of electrical conductivity on nanotube concentration decreases with increasing nanotube curl ratio. The conductivity exhibits an inverse power-law dependence on the curl ratio with a critical exponent in the range of 2.2-2.6. © 2007 Elsevier Ltd. All rights reserved.
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Electrical conductivity and damage sensing of carbon nanotube-based composites
American Society for Composites - 23rd Technical Conference of the American Society for Composites 2008, 2008Co-Authors: Chunyu Li, T W ChouAbstract:Multifunctional carbon nanotube-based nanocomposites offer tremendous potential to improve the material properties and reduce the weight at the same time. Electrically conductive nanotube-based nanocomposites offer the potential in enhancing electrostatic dissipation, electromagnetic interference shielding as well as corrosion resistance, weight reduction and processing flexibility. There have been numerous studies on the percolation threshold and electric conductivity of particle-and fiber-reinforced conductive composites. Researchers in recent years have shown more interests in carbon nanotube-based conductive nanocomposites. Recently, we have systematically studied the influence of various factors on the electric conductivity of carbon nanotube-based composite films by Monte Carlo simulations in order to explain the large variation of their electrical conductivity. These factors include contact resistance, waviness and alignment of Nanotubes. The wavy Nanotubes are generated by employing the technique we developed earlier and they may overlap in a two-dimensional domain. From the viewpoint of resistor circuits, there are only two sources of resistance for a percolating network of carbon Nanotubes. One is the resistance along the nanotube itself, and the other is the contact resistance between junction Nanotubes. The electric conductivity of carbon Nanotubes depends only on the type of nanotube (single-walled or multi-walled; metallic or semiconducting). But the contact resistance is affected by several factors such as contact area, contact gap, junction type (metallic/metallic or metallic/semiconducting), and so on. Previous studies indicate that the overall resistances of SWNT bundle-bundle networks are dominated by the contact resistance. We found that the contact resistance plays a more dominant role in carbon nanotube-based composites and concluded that the upper thickness limit of the insulating film between contacting Nanotubes for electric tunneling is 1.8 nm. The results of our Monte Carlo simulations indicate that the electrical conductivity of composites with wavy Nanotubes is lower than that of composites with straight Nanotubes. The critical exponent of the power-law dependence of electrical conductivity on the nanotube concentration decreases with increasing nanotube curl ratio. The modeling of nanotube network in damage sensing of nanotube-based composites will also be presented.
Erik T. Thostenson - One of the best experts on this subject based on the ideXlab platform.
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Effect of nanotube waviness on the electrical conductivity of carbon nanotube-based composites
Composites Science and Technology, 2008Co-Authors: Chunyu Li, Erik T. Thostenson, T W ChouAbstract:Abstract This paper reports the effect of nanotube waviness on the electrical conductivity of carbon nanotube-based composites using a percolation model. Wavy Nanotubes are approximated by elongated polygons, and the current-carrying backbones of percolation clusters in the composite are identified by the direct electrifying algorithm. The tunneling resistance due to an insulating film of matrix material between crossing Nanotubes is considered. Results of Monte Carlo simulations indicate that the electrical conductivity of composites with wavy Nanotubes are lower than that of composites with straight Nanotubes. The critical exponent of the power-law dependence of electrical conductivity on nanotube concentration decreases with increasing nanotube curl ratio. The conductivity exhibits an inverse power-law dependence on the curl ratio with a critical exponent in the range of 2.2–2.6.
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Effect of nanotube waviness on the electrical conductivity of carbon nanotube-based composites
Composites Science and Technology, 2008Co-Authors: Chunyu Li, Erik T. Thostenson, T W ChouAbstract:This paper reports the effect of nanotube waviness on the electrical conductivity of carbon nanotube-based composites using a percolation model. Wavy Nanotubes are approximated by elongated polygons, and the current-carrying backbones of percolation clusters in the composite are identified by the direct electrifying algorithm. The tunneling resistance due to an insulating film of matrix material between crossing Nanotubes is considered. Results of Monte Carlo simulations indicate that the electrical conductivity of composites with wavy Nanotubes are lower than that of composites with straight Nanotubes. The critical exponent of the power-law dependence of electrical conductivity on nanotube concentration decreases with increasing nanotube curl ratio. The conductivity exhibits an inverse power-law dependence on the curl ratio with a critical exponent in the range of 2.2-2.6. © 2007 Elsevier Ltd. All rights reserved.
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processing structure multi functional property relationship in carbon nanotube epoxy composites
Carbon, 2006Co-Authors: Erik T. Thostenson, T W ChouAbstract:The novel properties of carbon Nanotubes have generated scientific and technical interest in the development of nanotube-reinforced polymer composites. In order to utilize Nanotubes in multi-functional material systems it is crucial to develop processing techniques that are amenable to scale-up for high volume, high rate production. In this research we investigate a scalable calendering approach for achieving dispersion of CVD-grown multi-walled carbon Nanotubes through intense shear mixing. Electron microscopy was utilized to study the micro and nanoscale structure evolution during the manufacturing process and optimize the processing conditions for producing highly-dispersed nanocomposites. After processing protocols were established, nanotube/epoxy composites were processed with varying reinforcement fractions and the fracture toughness and electrical/thermal transport properties were evaluated. The as-processed nanocomposites exhibited significantly enhanced fracture toughness at low nanotube concentrations. The high aspect ratios of the carbon Nanotubes in the as-processed composites enabled the formation of a conductive percolating network at concentrations below 0.1% by weight. The thermal conductivity increased linearly with nanotube concentration to a maximum increase of 60% at 5 wt.% carbon Nanotubes.
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On the elastic properties of carbon nanotube-based composites: Modelling and characterization
Journal of Physics D: Applied Physics, 2003Co-Authors: Erik T. Thostenson, Tsu W. ChouAbstract:The exceptional mechanical and physical properties observed for carbon Nanotubes has stimulated the development of nanotube-based composite materials, but critical challenges exist before we can exploit these extraordinary nanoscale properties in a macroscopic composite. At the nanoscale, the structure of the carbon nanotube strongly influences the overall properties of the composite. The focus of this research is to develop a fundamental understanding of the structure/size influence of carbon Nanotubes on the elastic properties of nanotube-based composites. Towards this end, the nanoscale structure and elastic properties of a model composite system of aligned multi-walled carbon Nanotubes embedded in a polystyrene matrix were characterized, and a micromechanical approach for modelling of short fibre composites was modified to account for the structure of the nanotube reinforcement to predict the elastic modulus of the nanocomposite as a function of the constituent properties, reinforcement geometry and nanotube structure. The experimental characterization results are compared with numerical predictions and highlight the structure/size influence of the nanotube reinforcement on the properties of the nanocomposite. The nanocomposite elastic properties are particularly sensitive to the nanotube diameter, since larger diameter Nanotubes show a lower effective modulus and occupy a greater volume fraction in the composite relative to smaller-diameter Nanotubes.
Jeong Won Kang - One of the best experts on this subject based on the ideXlab platform.
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Carbon nanotube shuttle memory device based on singlewall-to-doublewall carbon nanotube transition
Computational Materials Science, 2005Co-Authors: Jeong Won Kang, Ho Jung HwangAbstract:Abstract This paper shows the schematics, the energetics, and the operations of nonvolatile-nanomemory-element based on carbon nanopeapods using classical molecular dynamics simulations. The system proposed was composed of one-side-capped (10, 10) and a (5, 5) carbon Nanotubes. The open ends of two (10, 10) carbon Nanotubes were face to face with the separation of 14 A distance. The inner C180 carbon nanotube, which was formed by the coalescence of three C60 molecules, shuttled between two (10, 10) carbon Nanotubes under the alternatively applied force fields. Since the inner carbon nanotube can hardly escape from the outer carbon Nanotubes without external force fields, the proposed system can operate a nonvolatile memory device. To switch the carbon nanotube shuttle system, the external electric fields to overcome the restoring force as well as the cap-capturing force should be applied. Classical molecular dynamics simulations showed that the carbon nanotube shuttle memory element could be operated by an adequate external force field.
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Copper nanocluster diffusion in carbon nanotube
Solid State Communications, 2004Co-Authors: Ho Jung Hwang, Oh-keun Kwon, Jeong Won KangAbstract:The diffusion of copper nanocluster in carbon nanotube was investigated using a classical molecular dynamics simulation and three empirical potential functions. The results indicated a growth mechanism of the copper-filled ultra-thin carbon Nanotubes: the copper nanoclusters inserted into carbon Nanotubes swiftly migrate along the tube axis, and then the copper nanowires grow in the ultra-thin carbon Nanotubes. Periodic energy barriers in the carbon Nanotubes induced the directional movement of copper nanoclusters in the carbon Nanotubes. The diffusion speeds of copper nanocluster in the carbon nanotube showed the Arrherius relation.
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Copper nanocluster diffusion in carbon nanotube
Solid State Communications, 2004Co-Authors: Ho Jung Hwang, Oh-keun Kwon, Jeong Won KangAbstract:The diffusion of copper nanocluster in carbon nanotube was investigated using a classical molecular dynamics simulation and three empirical potential functions. The results indicated a growth mechanism of the copper-filled ultra-thin carbon Nanotubes: the copper nanoclusters inserted into carbon Nanotubes swiftly migrate along the tube axis, and then the copper nanowires grow in the ultra-thin carbon Nanotubes. Periodic energy barriers in the carbon Nanotubes induced the directional movement of copper nanoclusters in the carbon Nanotubes. The diffusion speeds of copper nanocluster in the carbon nanotube showed the Arrherius relation. © 2004 Elsevier Ltd. All rights reserved.
Pulickel Madhavapanicker Ajayan - One of the best experts on this subject based on the ideXlab platform.
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Continuous carbon nanotube reinforced composites
Nano Letters, 2008Co-Authors: Longjun Ci, Victor Pushparaj, Jonghwan Suhr, Xiang Zhang, Xiaofeng Zhang, Pulickel Madhavapanicker AjayanAbstract:Carbon Nanotubes are considered short fibers, and polymer composites with nanotube fillers are always analogues of random, short fiber composites. The real structural carbon fiber composites, on the other hand, always contain carbon fiber reinforcements where fibers run continuously through the composite matrix. With the recent optimization in aligned nanotube growth, samples of Nanotubes in macroscopic lengths have become available, and this allows the creation of composites that are similar to the continuous fiber composites with individual Nanotubes running continuously through the composite body. This allows the proper utilization of the extreme high modulus and strength predicted for Nanotubes in structural composites. Here, we fabricate such continuous nanotube polymer composites with continuous nanotube reinforcements and report that under compressive loadings, the nanotube composites can generate more than an order of magnitude improvement in the longitudinal modulus (up to 3,300%) as well as damping capability (up to 2,100%). It is also observed that composites with a random distribution of Nanotubes of same length and similar filler fraction provide three times less effective reinforcement in composites.
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Super-compressible foamlike carbon nanotube films.
Science (New York, N.Y.), 2005Co-Authors: Anyuan Cao, Mehrdad N. Ghasemi-nejhad, Pamela L. Dickrell, W. Gregory Sawyer, Pulickel Madhavapanicker AjayanAbstract:We report that freestanding films of vertically aligned carbon Nanotubes exhibit super-compressible foamlike behavior. Under compression, the Nanotubes collectively form zigzag buckles that can fully unfold to their original length upon load release. Compared with conventional low-density flexible foams, the nanotube films show much higher compressive strength, recovery rate, and sag factor, and the open-cell nature of the nanotube arrays gives excellent breathability. The nanotube films present a class of open-cell foam structures, consisting of well-arranged one-dimensional units (nanotube struts). The lightweight, highly resilient nanotube films may be useful as compliant and energy-absorbing coatings.
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Direct synthesis of long single-walled carbon nanotube strands
Science, 2002Co-Authors: H.-w. Zhu, B. Q. Wei, D. H. Wu, C. L. Xu, Robert Vajtai, Pulickel Madhavapanicker AjayanAbstract:In the processes that are used to produce single-walled Nanotubes (electric arc, laser ablation, and chemical vapor deposition), the typical lengths of tangled nanotube bundles reach several tens of micrometers. We report that long nanotube strands, up to several centimeters in length, consisting of aligned single-walled Nanotubes can be synthesized by the catalytic pyrolysis of n-hexane with an enhanced vertical floating technique. The long strands of Nanotubes assemble continuously from arrays of Nanotubes, which are intrinsically long.
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large scale synthesis of carbon Nanotubes
Nature, 1992Co-Authors: Thomas W Ebbesen, Pulickel Madhavapanicker AjayanAbstract:INTEREST in carbon fibres1,2 has been stimulated greatly by the recent discovery of hollow graphitic tubules of nanometre dimensions3. There has been much speculation about the properties and potential application of these Nanotubes4–8. Theoretical studies predict that their electronic properties will depend on their diameter and degree of helicity4,5. Experimental tests of these ideas has been hampered, however, by the lack of macroscopic quantities of the material. Here we report the synthesis of graphitic Nanotubes in gram quantities. We use a variant of the standard arc-discharge technique for fullerene synthesis under a helium atmosphere. Under certain conditions, a carbonaceous deposit forms on one of the graphite rods, consisting of a macroscopic (diameter of about 5 mm) cylinder in which the core comprises pure Nanotubes and nanoscale particles in high yield. The purity and yield depend sensitively on the gas pressure in the reaction vessel. Preliminary measurements of the conductivity of the bulk nanotube material indicate a conductivity of about 100 S cm–11.
Ho Jung Hwang - One of the best experts on this subject based on the ideXlab platform.
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Carbon nanotube shuttle memory device based on singlewall-to-doublewall carbon nanotube transition
Computational Materials Science, 2005Co-Authors: Jeong Won Kang, Ho Jung HwangAbstract:Abstract This paper shows the schematics, the energetics, and the operations of nonvolatile-nanomemory-element based on carbon nanopeapods using classical molecular dynamics simulations. The system proposed was composed of one-side-capped (10, 10) and a (5, 5) carbon Nanotubes. The open ends of two (10, 10) carbon Nanotubes were face to face with the separation of 14 A distance. The inner C180 carbon nanotube, which was formed by the coalescence of three C60 molecules, shuttled between two (10, 10) carbon Nanotubes under the alternatively applied force fields. Since the inner carbon nanotube can hardly escape from the outer carbon Nanotubes without external force fields, the proposed system can operate a nonvolatile memory device. To switch the carbon nanotube shuttle system, the external electric fields to overcome the restoring force as well as the cap-capturing force should be applied. Classical molecular dynamics simulations showed that the carbon nanotube shuttle memory element could be operated by an adequate external force field.
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Copper nanocluster diffusion in carbon nanotube
Solid State Communications, 2004Co-Authors: Ho Jung Hwang, Oh-keun Kwon, Jeong Won KangAbstract:The diffusion of copper nanocluster in carbon nanotube was investigated using a classical molecular dynamics simulation and three empirical potential functions. The results indicated a growth mechanism of the copper-filled ultra-thin carbon Nanotubes: the copper nanoclusters inserted into carbon Nanotubes swiftly migrate along the tube axis, and then the copper nanowires grow in the ultra-thin carbon Nanotubes. Periodic energy barriers in the carbon Nanotubes induced the directional movement of copper nanoclusters in the carbon Nanotubes. The diffusion speeds of copper nanocluster in the carbon nanotube showed the Arrherius relation.
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Copper nanocluster diffusion in carbon nanotube
Solid State Communications, 2004Co-Authors: Ho Jung Hwang, Oh-keun Kwon, Jeong Won KangAbstract:The diffusion of copper nanocluster in carbon nanotube was investigated using a classical molecular dynamics simulation and three empirical potential functions. The results indicated a growth mechanism of the copper-filled ultra-thin carbon Nanotubes: the copper nanoclusters inserted into carbon Nanotubes swiftly migrate along the tube axis, and then the copper nanowires grow in the ultra-thin carbon Nanotubes. Periodic energy barriers in the carbon Nanotubes induced the directional movement of copper nanoclusters in the carbon Nanotubes. The diffusion speeds of copper nanocluster in the carbon nanotube showed the Arrherius relation. © 2004 Elsevier Ltd. All rights reserved.
