Japan's Showa Denko KK (SDK) has developed VGCF™-X, a new grade of SDK carbon nanotube (CNT) with an optimized design for resin composite applications. The company says it will begin construction of a 400 t/year plant to manufacture the new product at its Oita complex in March 2009. The plant, due to start up in 2010, will benefit from a cost-competitive position since it can fully utilize the existing utilities at the site.
Tuesday, June 23, 2009
Effects of carbon nanotubes on primary neurons and glial cells
Carbon nanotubes (CNTs) are among the most promising novel nanomaterials and their unique chemical and physical properties suggest an enormous potential for many areas of research and applications. As a consequence, the production of CNT-based material and thus the occupational and public exposure to CNTs will increase steadily. Although there is evidence that nanoparticles (NPs) can enter the nervous system via the blood stream, olfactory nerves or sensory nerves in the skin, there is still only little knowledge about possible toxic effects of CNTs on cells of the nervous system.The goal of the present study was to analyse the influences of single-walled CNTs (SWCNTs) with different degrees of agglomeration on primary cultures derived from chicken embryonic spinal cord (SPC) or dorsal root ganglia (DRG). As measured by the Hoechst assay treatment of mixed neuro-glial cultures with up to 30 μg/mL SWCNTs significantly decreased the overall DNA content. This effect was more pronounced if cells were exposed to highly agglomerated SWCNTs as compared to better dispersed SWCNT-bundles. Using a cell-based ELISA we found that SWCNTs reduce the amount of glial cells in both peripheral nervous system (PNS) and central nervous system (CNS) derived cultures. Neurons were only affected in DRG derived cultures, where SWCNT treatment resulted in a decreased number of sensory neurons, as measured by ELISA. Additionally, whole-cell patch recordings revealed a diminished inward conductivity and a more positive resting membrane potential of SWCNT treated DRG derived neurons compared to control samples.
The SWCNT suspensions used in this study induced acute toxic effects in primary cultures from both, the central and peripheral nervous system of chicken embryos. The level of toxicity is at least partially dependent on the agglomeration state of the tubes. Thus if SWCNTs can enter the nervous system at sufficiently high concentrations, it is likely that adverse effects on glial cells and neurons might occur.
(Larisa Belyanskaya, Stefan Weigel, Cordula Hirsch, Ursina Tobler, Harald F. Krug, and Peter Wick, NeuroToxicology, Article in Press, 2009, doi:10.1016/j.neuro.2009.05.005)
Showa Denko develops new CNT grade, cooperates with Hyperion
According to SDK, VGCF-X, which has been developed using the company's catalyst and synthesis technologies, has very high electrical conductivity and dispersibility. Average nanotube diameter is 15–20 nm and length 3 μm, significantly smaller in both dimensions than the company's existing VGCF grades. The new product can impart stable conductivity to resins at low loading levels and is therefore expected to find applications in static-free plastic cases for the carriage of semiconductor/hard disk media parts. Because of increased production of semiconductors with fine structures and hard disk media with higher densities, these plastic cases are required to have higher antistatic levels to prevent contamination to parts and to ensure cleanliness of the air in a clean room.
SDK began developing VGCF products in 1982 under the guidance of Professor Morinobu Endo of Shinshu University, one of the pioneers of CNT synthesis. The company established a high-volume production technology in 1988 and started up a 20 t/year commercial plant in 1996. Capacity was expanded to 100 t/year in 2007. In September 2008, SDK and Endo jointly developed an ultra-high-performance composite rubber for oil exploration/drilling applications using VGCF-S, a finer grade developed for composites. SDK has been expanding its fine carbon operation, centring on VGCF, as one of its growth businesses. The company plans to achieve sales of ¥40 billion from this business in 2015 by developing new applications as well as battery and composite applications.
In addition, SDK has concluded a patent cross-licence and supply agreement with Hyperion Catalysis International, Inc (Cambridge, MA, USA), which owns many key patents pertaining to materials and applications in the area of CNTs, including for resin composites. In exchange for certain payments, royalties and other considerations, SDK will be able to sell CNT-based products for use within a defined field in plastics under Hyperion's extensive patent portfolio. The supply agreement provides that SDK will purchase Hyperion's FIBRIL™ conductive, multi-walled CNT-based products for resale alongside its own product line. According to SDK and Hyperion, these licence and supply agreements will help both firms to maintain and grow their leading positions in the manufacture of CNT-based products for the promising composite market. The two companies have also identified other areas of mutual interest and have initiated discussions regarding possible joint R&D projects.
Hyperion has been manufacturing and selling its FIBRIL CNTs since 1983. Pre-mixed in a range of matrices, they are used in a growing number of automotive, electronics and other applications.
(Additives for Polymers, Volume 2009, Issue 3, March 2009, Pages 3-4 )
Contact: Showa Denko KK, 13-9, Shiba Daimon 1-Chome, Minato-ku, Tokyo 105-8518, Japan. Tel: +81 3 5470 3235, Web: www.sdk.co.jp
Or contact: Hyperion Catalysis International, Inc, 38 Smith Place, Cambridge, MA 02138, USA. Tel: +1 617 354 9678, Web: www.hyperioncatalysis.com
Electrophoretic deposition of carbon nanotube–ceramic nanocomposites
The purpose of this paper is to present an up-to-date comprehensive overview of current research progress in the development of carbon nanotube (CNT)–ceramic nanocomposites by electrophoretic deposition (EPD). Micron-sized and nanoscale ceramic particles have been combined with CNTs, both multiwalled and single-walled, using EPD for a variety of functional, structural and biomedical applications.Systems reviewed include SiO2/CNT, TiO2/CNT, MnO2/CNT, Fe3O4/CNT, hydroxyapatite (HA)/CNT and bioactive glass/CNT. EPD has been shown to be a very convenient method to manipulate and arrange CNTs from well dispersed suspensions onto conductive substrates. CNT–ceramic composite layers of thickness in the range <1–50 μm have been produced. Sequential EPD of layered nanocomposites as well as electrophoretic co-deposition from diphasic suspensions have been investigated. A critical step for the success of EPD is the prior functionalization of CNTs, usually by their treatment in acid solutions, in order to create functional groups on CNT surfaces so that they can be dispersed uniformly in solvents, for example water or organic media.
The preparation and characterisation of stable CNT and CNT/ceramic particle suspensions as well as relevant EPD mechanisms are discussed. Key processing stages, including functionalization of CNTs, tailoring zeta potential of CNTs and ceramic particles in suspension as well as specific EPD parameters, such as deposition voltage and time, are discussed in terms of their influence on the quality of the developed CNT/ceramic nanocomposites. The analysis of the literature confirms that EPD is the technique of choice for the development of complex CNT–ceramic nanocomposite layers and coatings of high structural homogeneity and reproducible properties. Potential and realised applications of the resulting CNT–ceramic composite coatings are highlighted, including fuel cell and supercapacitor electrodes, field emission devices, bioelectrodes, photocatalytic films, sensors as well as a wide range of functional, structural and bioactive coatings. (A.R. Boccaccini, J. Cho, T. Subhani, C. Kaya and F. Kaya, Journal of the European Ceramic Society, Article in Press, 2009, doi:10.1016/j.jeurceramsoc.2009.03.016)
Electrochemical properties of interface formed by interlaced layers of DNA- and lysozyme-coated single-walled carbon nanotubes
Multifunctional coatings were produced by the layer by layer assembly of single-walled carbon nanotubes (SWNT) dispersed in DNA and lysozyme (LSZ) on an insulating glass substrate. The electrochemical properties of these mechanically robust biocoatings were characterized for the first time using scanning electrochemical microscopy (SECM) and impedance spectroscopy (IS). SECM surface analysis demonstrated an increase in tip current with a corresponding increase in the number of oppositely polarized interlaced layers, indicating that subsequent layers were not electrically insulated from each other and a direct correlation exists between SECM feedback response and the number of layers.
The rate of charge transport was also dependent on the chemical composition/polarity of the outermost surface layer. Coatings terminating in SWNT-DNA resulted in more positive feedback than those terminating in SWNT-LSZ. IS analysis demonstrated that the SWNT-DNA had a low charge transfer resistance in comparison with SWNT-LSZ, which is consistent with the results obtained by SECM. These results enable enhanced fundamental understanding and prediction of the electrical properties of SWNT-biopolymer layers with controlled interlaced polarities and orientation. Furthermore, these finding highlight the potential for SWNT-biopolymers in electronic and sensing applications.
(Valber A. Pedrosa, Tony Gnanaprakasa, Shankar Balasubramanian, Eric V. Olsen, Virginia A. Davis, and Aleksandr L. Simonian, Electrochemistry Communications, Article in Press, 2009, doi:10.1016/j.elecom.2009.05.016)
The rate of charge transport was also dependent on the chemical composition/polarity of the outermost surface layer. Coatings terminating in SWNT-DNA resulted in more positive feedback than those terminating in SWNT-LSZ. IS analysis demonstrated that the SWNT-DNA had a low charge transfer resistance in comparison with SWNT-LSZ, which is consistent with the results obtained by SECM. These results enable enhanced fundamental understanding and prediction of the electrical properties of SWNT-biopolymer layers with controlled interlaced polarities and orientation. Furthermore, these finding highlight the potential for SWNT-biopolymers in electronic and sensing applications.
(Valber A. Pedrosa, Tony Gnanaprakasa, Shankar Balasubramanian, Eric V. Olsen, Virginia A. Davis, and Aleksandr L. Simonian, Electrochemistry Communications, Article in Press, 2009, doi:10.1016/j.elecom.2009.05.016)
Preparation and characterization of highly conductive transparent films with single-walled carbon nanotubes for flexible display applications
Dense, aligned single-walled carbon nanotubes (SWCNTs) were obtained by nitric acid treatment and the subsequent removal of metal impurities by HCl. The highly purified SWCNTs were dispersed with sodium dodecyl sulfate in order to obtain a stabilized suspension for spray coating on flexible polyethylene terephthalate (PET) substrate. The low sheet resistance of the resulting thin conductive film on the PET substrate was due to the interconnecting networks of highly purified SWCNT bundles. These bundles formed strong crisscross networks of nanotubes clustered together with well defined channels, thus improving the electrical and optical properties of the film. Its sheet resistance varied from 956 to 472 Ω/square with 85% optical transmittance at a wavelength of 550 nm. The films may be potential candidates for flexible display applications.
(Santhosh Paul and Dong-Won Kim, Carbon, Article in Press, 2009,
doi:10.1016/j.carbon.2009.04.045)
(Santhosh Paul and Dong-Won Kim, Carbon, Article in Press, 2009,
doi:10.1016/j.carbon.2009.04.045)Molecular imaging with single-walled carbon nanotubes
Nanoparticle-based molecular imaging has emerged as an interdisciplinary field which involves physics, chemistry, engineering, biology, and medicine. Single-walled carbon nanotubes (SWCNTs) have unique properties which make them suitable for applications in a variety of imaging modalities, such as magnetic resonance, near-infrared fluorescence, Raman spectroscopy, photoacoustic tomography, and radionuclide-based imaging. In this review, we will summarize the current state-of-the-art of SWCNTs in molecular imaging applications. Multifunctionality is the key advantage of nanoparticles over traditional approaches. Targeting ligands, imaging labels, therapeutic drugs, and many other agents can all be integrated into the nanoparticle to allow for targeted molecular imaging and molecular therapy by encompassing many biological and biophysical barriers. A multifunctional, SWCNT-based nanoplatform holds great potential for clinical applications in the future.Carbon nanotube-based transducers for immunoassays
The attachment of mouse immunoglobulin G (IgG) and anti-mouse IgG antibodies onto carbon nanotubes (CNTs), using either non-covalent or covalent means was investigated. The resultant CNTs were characterised using a variety of techniques including enzyme-linked and fluorescence-linked immunoassays, UV–visible-NIR and Raman spectroscopy, transmission electron microscopy and cyclic voltammetry.
TEM images of the adsorbed antibody on the CNTs show that the covalent modification approach was successful, whereas the non-covalent approach resulted in no electrochemically detectable labelled antibody. Direct electrical communication between CNTs covalently linked to peroxidase-labelled antibodies was observed during cyclic voltammetry, which suggests applications in developing carbon-nanotube-based immunosensors.
(Carol Lynam, Niamh Gilmartin, Andrew I. Minett, Richard O’Kennedy, and Gordon Wallace, Carbon, Article in Press, 2009, doi:10.1016/j.carbon.2009.04.017)
TEM images of the adsorbed antibody on the CNTs show that the covalent modification approach was successful, whereas the non-covalent approach resulted in no electrochemically detectable labelled antibody. Direct electrical communication between CNTs covalently linked to peroxidase-labelled antibodies was observed during cyclic voltammetry, which suggests applications in developing carbon-nanotube-based immunosensors.
(Carol Lynam, Niamh Gilmartin, Andrew I. Minett, Richard O’Kennedy, and Gordon Wallace, Carbon, Article in Press, 2009, doi:10.1016/j.carbon.2009.04.017)
Controllable fabrication of carbon nanotube-polymer hybrid thin film for strain sensing
A strain sensing material based on carbon nanotubes-polymer hybrid film has been fabricated by the vacuum filtration and poly(dimethylsiloxane) (PDMS) molding transfer methods. The density and thickness of the film is tuned by simply controlling the volume of dilute suspension filtered through the membrane. These composites are resilient under large strain and there is a wide linear range of resistance–strain dependence. We demonstrate that the thin films with thicker CNTs networks exhibit more significant resistance–strain sensitivity under the same stain and the strain sensing material shows reproducible resistance–strain sensitivity depending only on the initial CNTs suspension volume. It may be possible to fabricate strain sensing material in large volume for future smart device applications.
(Xiaohui Song, Sheng Liu, Zhiyin Gan, Qiang Lv, Hui Cao, and Han Yan, Microelectronic Engineering, Article in Press, 2009,doi:10.1016/j.mee.2009.04.012)
(Xiaohui Song, Sheng Liu, Zhiyin Gan, Qiang Lv, Hui Cao, and Han Yan, Microelectronic Engineering, Article in Press, 2009,
doi:10.1016/j.mee.2009.04.012)
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