Organic polymers, such as poly͑vinyl alcohol͒, poly͑vinyl pyrrolidone͒, and poly͑styrene͒, were intercalated into single-walled carbon nanotube sheets by soaking the sheets in polymer solutions. Even for short soak times, significant polymer intercalation into existing free volume was observed. Tensile tests on intercalated sheets showed that the Young's modulus, strength, and toughness increased by factors of 3, 9, and 28, respectively, indicating that the intercalated polymer enhances load transmission between nanotubes. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1559421͔Realization of the applications potential of carbon single-walled nanotubes ͑SWNT͒ has been hindered by the many difficulties associated with their processing. Fabricating low-density carbon nanotube powder into functional macroscale structures has been a major challenge. Some progress has been made recently with the fabrication of one-, two-, and three-dimensional bulk nanotube material in the form of fibers, 1,2 sheets, 3 and Bucky Pearls™ pellets produced by Carbon Nanotechnologies Incorporated ͑CNI͒. However, while individual SWNTs display impressive Young's moduli and strengths of approximately 640 and 40 GPa, 4,5 respectively, the mechanical properties of the bulk materials remain disappointing. These low-bulk mechanical properties are in part because the individual SWNT usually forms 10-50-nm-diameter bundles that are only weakly bound by van der Waals interactions at junction points.Both carbon multiwalled nanotubes ͑MWNTs͒ and SWNTs have been used as reinforcing agents in polymer and epoxy composites. [6][7][8] Ideally, any load applied to the polymer matrix is transferred to the nanotubes. This load transfer relies on effective interfacial stress transfer at the polymernanotube interface, which tends to be polymer dependent. 8 This reinforcement technique has met with some success, providing increases in Young's modulus by a factor of 1.8 for 1 wt % loading of MWNTs in poly͑vinyl alcohol͒ ͑PVA͒ 8 and increases in hardness by a factor of 3.5 for 2 wt % loading of SWNTs in epoxy. 7 In this letter, we show that the reverse procedure of polymer intercalation can be used to reinforce bulk nanotube materials. Binding agents such as organic polymers can be intercalated into the porous internal structure of nanotube materials such as SWNT sheets ͑Buckypaper͒. This intercalation can be obtained by simply soaking the nanotube sheets in polymer solutions. The resulting polymer-intercalated sheets display improvements in Young's modulus and tensile strength by factors of ϳ3 and ϳ9, respectively.The nanotube sheets ͑Buckypaper͒ used in this work were prepared by filtration of SWNTs dispersed in water and Triton X-100, as previously described. 3 The SWNTs were made by the HiPco process and supplied by CNI. 9 This material is known to contain ϳ20 wt % iron ͑ϳ2 vol % for sheets͒. The carbon nanotube sheets were annealed under flowing argon at up to 1000°C before use, in order to remove residual surfactant, solvents, and contaminants. Thes...
Nanotube sheets, or ‘‘bucky papers,’ ’ have been proposed for use in actuating, structural and electrochemical systems, based in part on their potential mechanical properties. Here, we present results of detailed simulations of networks of nanotubes/ropes, with special emphasis on the effect of joint morphology. We perform detailed simulations of three-dimensional joint deformation, and use the results to inform simulations of two-dimensional �2D � networks with intertube connections represented by torsion springs. Upper bounds are established on moduli of nanotube sheets, using the 2D Euler beam-network simulations. Comparisons of experimental and simulated response for HiPco-nanotube and laser-ablated nanotube sheets, indicate that �2–30-fold increases in moduli may be achievable in these materials. Increasing the numbers of interrope connections appears to be the best target for improving nanotube sheet stiffnesses in materials containing straight segments. © 2004 American Institute of Physics. �DOI: 10.1063/1.1687995� I
Carbon nanotubes have long been of interest as additives for increasing the mechanical and electronic properties of polymers, and considerable progress has been made.[1±6] However, melt-phase and solution viscosities ordinarily become too high for conventional processing when the nanotube component exceeds about 10 wt.-%, which limits the nanotube contribution to composite properties. In a groundbreaking development, Vigolo et al. have shown that composite fibers comprising largely nanotubes can be obtained by a process called polyvinyl alcohol (PVA) coagulation spinning. [7±9] In this process, a dilute surfactant-assisted single-walled carbon nanotube (SWNT) dispersion is coagulated into a gel state by spinning it into an aqueous PVA solution; this is followed by conversion into a solid fiber by a slow draw process, during which the water in the gel evaporates. [7±9] We recently reported improvements in this fiber-spinning technique that dramatically increased fiber strength and fiber-spinning rate.[10±12]These improved fibers (comprised of about 60 % SWNTs in a PVA matrix) have a capacity to absorb energy (a specific toughness of about 600 J g ±1 ) that is much higher than any other natural or synthetic organic fiber. Additionally, these SWNT fibers have been successfully utilized in the fabrication of electrochemical devices, such as electromechanical actuators [1,12] and supercapacitors. [10,11] However, unless the polymer is removed by pyrolysis (which degrades the mechanical properties of the fiber), performance of these electrochemical devices is limited by the low electrical conductivity of the nanotube/polymer composite fibers and degradation of mechanical stability when the PVA in these fibers is converted into an ionic conductor. [11] We show here that fibers with useful mechanical properties can be spun if we replace the PVA coagulant with a polyethyleneimine (PEI) coagulant. Although the PEI used is ordinarily a liquid at room temperature, it interacts with the nanotubes to serve as an intertube binding agent. The resulting strain-to-failure and toughness of the PEI-containing fibers are far greater than those of the thermally annealed, binder-free SWNT fibers (which have the advantage of a somewhat higher tensile strength and electrical conductivity) that were spun using the pioneering superacid method developed by the Rice group. [13,14] While the fiber strength and toughness achieved here are far less than those of fibers obtained from the continuous spinning process of Dalton et al. for producing SWNT/PVA composite fibers, [10,11] the prospects of improving the mechanical properties of the SWNT/PEI fibers appear good. Moreover, the electrical conductivity of the SWNT/PEI composite fibers is over a hundred times that of the supertough SWNT/PVA composite fibers. PEI and, in general, amines, are known to effectively interact with carbon nanotubes via physisorption on the nanotubes' sidewalls.[15±21] Thus, a method for separating metallic and semiconducting SWNTs has been developed that uses the hi...
Carbon nanotubes have been the focus of considerable research over the last decade. Because of their remarkable structural, mechanical, electrical, and thermal properties, [1] diverse applications have been envisioned. [2] Realization of these property advantages has been frustrated by material heterogeneity and impurities: catalyst and/or impurity carbons are present and as-produced nanotubes are mixtures of moderate bandgap semiconductors, very small bandgap semiconductors, and metallic conductors. Also, single-wall nanotubes (SWNTs) aggregate into bundles and larger, morerandom assemblies, and are difficult to uniformly disperse in melt or solution as either bundles or individual nanotubes. [3] Nanomanipulation techniques have been used for fabricating single-nanotube devices, such as sensors and field effect transistors, [4±6] but the probability of selecting the proper nanotubes needed for device function is low and these techniques are generally much too inefficient and unreliable to be used for making commercial practice. Nevertheless, strategies have been developed and practiced in the laboratory for fabricating carbon nanotube forests and other oriented nanotube assemblies (which can be used for field emitting devices), [7,8] self-standing carbon nanotube films (the so-called ªbucky-papersº), [9,10] and polymer and ceramic composites. [2,11±15] The addition of carbon nanotubes to polymeric or epoxy matrices results in composites with enhanced mechanical properties and electronic transport. [2,11,13] Composites of multiwall nanotubes (MWNTs) have been employed for initial practical applications, such as enabling electrostatic painting of automotive parts, and are of great interest for radio-frequency and electromagnetic shielding. [2,16] We have recently shown that intercalation of polymers in the porous structure of nanotube sheets increases Young's modulus, strength and toughness by factors of up to 3, 9, and 28, respectively. [17] The fabrication of carbon nanotube containing fibers is of special interest for mechanical and electronic textile applications. [18,19] Vigolo et al. developed an innovative coagulationbased fiber spinning technique: first, an aqueous dispersion of arc-discharge-produced single-wall carbon nanotubes (SWNTs) and surfactant (sodium dodecyl sulfate) is injected into a rotating bath of aqueous polyvinyl alcohol (PVA) solution, which serves as coagulant. [20±22] The nanotubes collapse during coagulation to form ribbon-like elastomeric gel-fibers. [23] Such gel-fibers are washed by immersion in successive water containers to remove excess PVA, and then dried by pulling from the water bath. The gel-fibers spun by this technique are difficult to disentangle and too weak to be easily handled. As a result, the produced dried fibers were typically short (some tens of centimeters long). Tensile strength and Young's modulus values of up to 230 MPa and 40 GPa, respectively, were reported for those dried SWNT/ PVA composite fibers. [20±22] This coagulation-based fiber spinning techniq...
The controlled addition of La to HfxSi1−xO2/SiO2/Si dielectric stacks has been shown to enable the engineering of the work function to appropriate levels when TaN or TiN is employed as the capping metal gate. Work function tuning has been suggested to be controlled by La diffusion into the Hf-based dielectric as a result of further thermal treatments. In this paper, we performed high resolution angle resolved x-ray photoelectron spectroscopy (ARXPS) studies to investigate the chemical depth profile distribution of TaN/La2O3/HfO2/SiO2/Si dielectric stacks exposed to a nitridation treatment by NH3 at 700 °C. The stoichiometry and distribution of the HfO2 and SiO2 layers was examined using a self-consistent ARXPS analysis. This study shows that La diffuses to the SiO2/HfO2 interface, and that subsequent rapid thermal annealing at 1000 °C for 5 s does not significantly change the La distribution.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.