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Jonathan N Coleman - One of the best experts on this subject based on the ideXlab platform.
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multicomponent solubility parameters for single walled carbon Nanotube solvent mixtures
ACS Nano, 2009Co-Authors: Shane D Bergin, Zhenyu Sun, David Rickard, Philip V Streich, James P Hamilton, Jonathan N ColemanAbstract:We have measured the dispersibility of single-walled carbon Nanotubes in a range of solvents, observing values as high as 3.5 mg/mL. By plotting the Nanotube dispersibility as a function of the Hansen solubility parameters of the solvents, we have confirmed that successful solvents occupy a well-defined range of Hansen parameter space. The level of dispersibility is more sensitive to the dispersive Hansen parameter than the polar or H-bonding Hansen parameter. We estimate the dispersion, polar, and hydrogen bonding Hansen parameter for the Nanotubes to be = 17.8 MPa(1/2), = 7.5 MPa(1/2), and = 7.6 MPa(1/2). We find that the Nanotube dispersibility in good solvents decays smoothly with the distance in Hansen space from solvent to Nanotube solubility parameters. Finally, we propose that neither Hildebrand nor Hansen solubility parameters are fundamental quantities when it comes to Nanotube-solvent interactions. We show that the previously calculated dependence of Nanotube Hildebrand parameter on Nanotube diameter can be reproduced by deriving a simple expression based on the Nanotube surface energy. We show that solubility parameters based on surface energy give equivalent results to Hansen solubility parameters. However, we note that, contrary to solubility theory, a number of nonsolvents for Nanotubes have both Hansen and surface energy solubility parameters similar to those calculated for Nanotubes. The nature of the distinction between solvents and nonsolvents remains to be fully understood.
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enhancement of modulus strength and toughness in poly methyl methacrylate based composites by the incorporation of poly methyl methacrylate functionalized Nanotubes
Advanced Functional Materials, 2006Co-Authors: David Blond, Kevin P. Ryan, Werner J Blau, Valeria Nicolosi, Manuel Ruether, Valerie Barron, Jonathan N ColemanAbstract:Poly(methyl methacrylate) (PMMA)-functionalized multiwalled carbon Nanotubes are prepared by in situ polymerization. Infrared absorbance studies reveal covalent bonding between polymer strands and the Nanotubes. These treated Nanotubes are blended with pure PMMA in solution before drop-casting to form composite films. Increases in Young’s modulus, breaking strength, ultimate tensile strength, and toughness of ×1.9, ×4.7, ×4.6, and ×13.7, respectively, are observed on the addition of less than 0.5 wt% of Nanotubes. Effective reinforcement is only observed up to a Nanotube content of approximately 0.1 vol%. Above this volume fraction, all mechanical parameters tend to fall off, probably due to Nanotube aggregation. In addition, scanning electron microscopy (SEM) studies of composite fracture surfaces show a polymer layer coating the Nanotubes after film breakage. The fact that the polymer and not the interface fails suggests that functionalization results in an extremely high polymer/Nanotube interfacial shear strength.
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Biomolecules as selective dispersants for carbon Nanotubes
Carbon, 2005Co-Authors: Simon Edward Moulton, Kevin P. Ryan, Denis Mccarthy, Andrew I Minett, Werner J Blau, Robert Murphy, Jonathan N Coleman, Gordon G WallaceAbstract:Abstract Both single-wall or multi-wall Nanotube growth result in a soot-like material that contains the desired product. The selective recovery of the Nanotube product from this soot still represents a challenge. Methods to date either result in chemical modification of the Nanotubes themselves, are time consuming or use expensive to produce polymers. Using a variety of biomolecules, we have been able to selectively suspend multi-wall carbon Nanotubes in aqueous solutions while leaving behind the extraneous by-products in the precipitate. At comparable biomolecule to soot ratios, all biomolecules selectively retained more Nanotubes than an organic polymer previously used to purify multi-wall Nanotubes (PmPV—poly m-phenylene-co-2,5-dioctoxy-p-phenylenevinylene). The highest recovery as determined by Electron Paramagnetic Resonance was 56% of the available Nanotubes. The method provides a simple, one-step, non-destructive purification process that facilitates the formation of pure multi-wall carbon Nanotube containing biodispersions.
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Reinforcement of polymers with carbon Nanotubes: The role of Nanotube surface area
Nano Letters, 2004Co-Authors: Martin Cadek, Kevin P. Ryan, Jonathan N Coleman, Valeria Nicolosi, Antonio Fonseca, G. Bister, Janos B. Nagy, K. Szostak, François Béguin, Werner J BlauAbstract:Tensile tests were carried out on free-standing composite films of poly(vinyl alcohol) and six different types of carbon Nanotubes for different Nanotube loading levels. Significant increases in Young's modulus by up to a factor of 2 were observed in all cases. Theories such as the rule-of-mixtures or the Halpin-Tsai-theory could not explain the relative differences between composites made from different tube types. However, it is possible to show that the reinforcement scales linearly with the total Nanotube surface area in the films, indicating that low diameter multiwall Nanotubes are the best tube type for reinforcement. In addition, in all cases crystalline coatings around the Nanotubes were detected by calorimetry, suggesting comparible polymer−Nanotube interfaces. Thus, the reinforcement appears to be critically dependent on the polymer−Nanotube interfacial interaction as previously suggested.
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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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.
Hongjie Dai - One of the best experts on this subject based on the ideXlab platform.
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ballistic transport in metallic Nanotubes with reliable pd ohmic contacts
Nano Letters, 2003Co-Authors: David G J Mann, Qian Wang, Ali Javey, Jing Kong, Hongjie DaiAbstract:Contacting metallic single-walled carbon Nanotubes by palladium (Pd) affords highly reproducible ohmic contacts and allows for the detailed elucidation of ballistic transport in metallic Nanotubes. The Pd ohmic contacts are more reliable than the titanium (Ti) previously used for ballistic Nanotube devices. In contrast, Pt contacts appear to give nonohmic contacts to metallic Nanotubes. For both ohmic and nonohmic contacts, the length of the Nanotube under the metal contact area is electrically turned off. Transport occurs from metal to Nanotube at the edges of the contacts. Measurements with large numbers of Pd-contacted Nanotube samples reveal that the mean free path for defect scattering in SWNTs grown by chemical vapor deposition can be up to 4 Im. The mean free paths for acoustic phonon scattering are on the order of 500 nm at room temperature and .4 Im at low temperatures. Ohmic contacts with minimum contact resistance are important to the fundamental characterization and realization of high-performance devices of electronic materials. Ohmic contacts to individual metallic single-walled carbon Nanotubes (m-SWNTs) by Cr and Ti have enabled the observation
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ballistic transport in metallic Nanotubes with reliable pd ohmic contacts
arXiv: Condensed Matter, 2003Co-Authors: David G J Mann, Qian Wang, Ali Javey, Jing Kong, Hongjie DaiAbstract:Contacting metallic single-walled carbon Nanotubes by palladium (Pd) affords highly reproducible ohmic contacts and allows for detailed elucidation of ballistic transport in metallic Nanotubes. The Pd ohmic contacts are more reliable than titanium (Ti) previously used for ballistic Nanotube devices. In contrast, Pt contacts appear to give non-ohmic contacts to metallic Nanotubes. For both ohmic and non-ohmic contacts, the length of the Nanotube under the metal contact area is electrically turned off. Transport occurs from metal to Nanotube at the edges of the contacts. Measurements with large numbers of Pd contacted Nanotube samples reveal that the mean free path for defect scattering in SWNTs grown by chemical vapor deposition can be up to 4 microns. The mean free paths for acoustic phonon scattering are on the order of 500 nm at room temperature and >> 4 microns at low temperatures.
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carbon Nanotubes opportunities and challenges
Surface Science, 2002Co-Authors: Hongjie DaiAbstract: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.
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Self-oriented regular arrays of carbon Nanotubes and their field emission properties
Science, 1999Co-Authors: Shoushan Fan, Michael G. Chapline, Thomas W. Tombler, Nathan R. Franklin, Alan M Cassell, Hongjie DaiAbstract:The synthesis of massive arrays of monodispersed carbon Nanotubes that are self-oriented on patterned porous silicon and plain silicon substrates is reported. The approach involves chemical vapor deposition, catalytic particle size control by substrate design, Nanotube positioning by patterning, and Nanotube self-assembly for orientation. The mechanisms of Nanotube growth and self-orientation are elucidated. The well-ordered Nanotubes can be used as electron field emission arrays. Scaling up of the synthesis process should be entirely compatible with the existing semiconductor processes, and should allow the development of Nanotube devices integrated into silicon technology.
T. W. Chou - 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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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.
Sungwoo Yang - One of the best experts on this subject based on the ideXlab platform.
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orthogonal orientation control of carbon Nanotube growth
Journal of the American Chemical Society, 2010Co-Authors: Weiwei Zhou, Lei Ding, Sungwoo YangAbstract:Carbon Nanotubes (CNTs) have attracted attention for their remarkable electrical properties and have being explored as one of the best building blocks in nano-electronics. A key challenge to realize such potential is the control of the Nanotube growth directions. Even though both vertical growth and controlled horizontal growth of carbon Nanotubes have been realized before, the growth of complex Nanotube structures with both vertical and horizontal orientation control on the same substrate has never been achieved. Here, we report a method to grow three-dimensional (3D) complex Nanotube structures made of vertical Nanotube forests and horizontal Nanotube arrays on a single substrate and from the same catalyst pattern by an orthogonally directed Nanotube growth method using chemical vapor deposition (CVD). More importantly, such a capability represents a major advance in controlled growth of carbon Nanotubes. It enables researchers to control the growth directions of Nanotubes by simply changing the reactio...
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Orthogonal orientation control of carbon Nanotube growth.
Journal of the American Chemical Society, 2010Co-Authors: Weiwei Zhou, Sungwoo Yang, Lei Ding, Jie LiuAbstract:Carbon Nanotubes (CNTs) have attracted attention for their remarkable electrical properties and have being explored as one of the best building blocks in nano-electronics. A key challenge to realize such potential is the control of the Nanotube growth directions. Even though both vertical growth and controlled horizontal growth of carbon Nanotubes have been realized before, the growth of complex Nanotube structures with both vertical and horizontal orientation control on the same substrate has never been achieved. Here, we report a method to grow three-dimensional (3D) complex Nanotube structures made of vertical Nanotube forests and horizontal Nanotube arrays on a single substrate and from the same catalyst pattern by an orthogonally directed Nanotube growth method using chemical vapor deposition (CVD). More importantly, such a capability represents a major advance in controlled growth of carbon Nanotubes. It enables researchers to control the growth directions of Nanotubes by simply changing the reaction conditions. The high degree of control represented in these experiments will surely make the fabrication of complex Nanotube devices a possibility.
