781 resultados para polyaniline nanotubes
Resumo:
The van der Waals (vdW) interactions between carbon nanotubes (CNTs) were studied based on the continuum Lennard-Jones model. It was found that all the vdW potentials between two arbitrary CNTs fall on the same curve when plotted in terms of certain reduced parameters, the well depth, and the equilibrium vdW gap. Based on this observation, an approximate approach is developed to obtain the vdW potential between two CNTs without time-consuming computations. The vdW potential estimated by this approach is close to that obtained from complex integrations. Therefore, the developed approach can greatly simplify the calculation of vdW interactions between CNTs.
Resumo:
Carbon nanotubes (CNT) are well-ordered, high aspect ratio allotropes of carbon. The two main variants, single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT) both possess a high tensile strength, are ultra-light weight, and have excellent chemical and thermal stability. They also possess semi- and metallic-conductive properties. This startling array of features has led to many proposed applications in the biomedical field, including biosensors, drug and vaccine delivery and the preparation of unique biomaterials such as reinforced and/or conductive polymer nanocomposites. Despite an explosion of research into potential devices and applications, it is only recently that information on toxicity and biocompatibility has become available. This review presents a summary of the performance of existing carbon biomaterials and gives an outline of the emerging field of nanotoxicology, before reviewing the available and often conflicting investigations into the cytotoxicity and biocompatibility of CNT. Finally, future areas of investigation and possible solutions to current problems are proposed. (c) 2005 Elsevier Ltd. All rights reserved.
Resumo:
This paper reports a study on nanostructured magnesium composites with carbon nanotubes (CNTs) and catalytic transition metals with high H-2 adsorption capacity and fast adsorption kinetics at reduced hydrogenation temperatures. Nanostructures in such a composite are shown to be responsible for improvements in both adsorption capacity and kinetics. It is found that the carbon nanotubes significantly increase the hydrogen storage capacity, and the catalytic transition metals (Fe and Ti) greatly improve the kinetics. This could be understood from the enhancement of diffusion by CNTs and decrease in energy barrier of hydrogen dissociation at the magnesium surface.
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A new poly(ethylene oxide)-tetraphenylalanine polymer-peptide conjugate has been prepared via a “click” reaction between an alkyne-modified peptide and an azide-terminated PEO oligomer. Self-assembled nanotubes are formed after dialysis of a THF solution of this polymer-peptide conjugate against water. The structure of these nanotubes has been probed by circular dichroism, IR, TEM, and SAXS. From these data, it is apparent that self-assembly involves the formation of antiparallel ß-sheets and p-p-stacking. Nanotubes are formed at concentrations between 2 and 10 mg mL-1. Entanglement between adjacent nanotubes occurs at higher concentrations, resulting in the formation of soft hydrogels. Gel strength increases at higher polymer-peptide conjugate concentration, as expected.
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We extract the distribution of both center-of-mass and angular fluctuations from three-dimensional tracking of optically trapped nanotubes. We measure the optical force and torque constants from autocorrelation and cross-correlation of the tracking signals. This allows us to isolate the angular Brownian motion. We demonstrate that nanotubes enable nanometer spatial and femtonewton force resolution in photonic force microscopy, the smallest to date. This has wide implications in nanotechnology, biotechnology, nanofluidics, and material science.
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We report an all-fiber mode-locked erbium-doped fiber laser (EDFL) employing carbon nanotube (CNT) polymer composite film. By using only standard telecom grade components, without any complex polarization control elements in the laser cavity, we have demonstrated polarization locked vector solitons generation with duration of ~583fs , average power of ~3 mW (pulse energy of 118pJ ) at the repetition rate of ~25.7 MHz.
Resumo:
Electrical and thermal transport properties of the carbon nanotube bulk material compacted by spark plasma sintering have been investigated. The electrical conductivity of the as-prepared sample shows a lnT dependence from 4 to 50 K, after which the conductivity begins to increase approximately linearly with temperature. A magnetic field applied perpendicularly to the sample increases the electrical conductivity in the range of 0-8T at all testing temperatures, indicating that the sample possesses the two-dimensional weak localization at lower temperatures (?50 K), while behaviors like a semimetal at higher temperatures (?50 K). This material acts like a uniform compact consisting of randomly distributed two dimensional graphene layers. For the same material, the thermal conductivity is found to decrease almost linearly with decreasing temperature, similar to that of a single multi-walled carbon nanotube. Magnetic fields applied perpendicularly to the sample cause the thermal conductivity to decrease significantly, but the influence of the magnetic fields becomes weak when temperature increases.
Resumo:
The surfaces of bulk carbon nanotubes compacted by plasma spark sintering have been modified with polytetrofluorethylene, thereby producing a super-hydrophobic surface with a contact angle above 160°. The surface roughness and air trapped in pores and between the polytetrofluorethylene particles are responsible for the super-hydrophobility. The material can be machined into desired shapes with fine and complex channels, allowing internal surfaces to also be super-hydrophobic.
Resumo:
Graphene layers have been produced from multi-walled carbon nanotube (MWCNT) bulk materials by friction when polished on ground-glass, offering a novel and effective method to produce graphene layers, which, more importantly, could be transferred to other substrates by rubbing. Field emission scanning electron microscopy, Raman spectroscopy, atomic force microscopy, transmission electron microscopy and selected area electron diffraction confirmed the formation of graphene layers. They were thought to be peeled away from the MWCNT walls due to friction. The reflection spectra showed that absorption of as-produced graphene layers decreased with wavelength in the range of 250–400 nm, compared to the MWCNT bulk material having strong absorption at 350 nm. Nanoscratch test was used to determine the mechanical properties of graphene films, suggesting the tolerance of as-produced graphene film to flaws introduced by scratch.
Resumo:
Hydrogels containing carbon nanotubes (CNTs) are expected to be promising conjugates because they might show a synergic combination of properties from both materials. Most of the hybrid materials containing CNTs only entrap them physically, and the covalent attachment has not been properly addressed yet. In this study, single-walled carbon nanotubes (SWNTs) were successfully incorporated into a poly(ethylene glycol) (PEG) hydrogel by covalent bonds to form a hybrid material. For this purpose, SWNTs were functionalized with poly(ethylene glycol) methacrylate (PEGMA) to obtain water-soluble pegylated SWNTs (SWNT–PEGMA). These functionalized SWNTs were covalently bonded through their PEG moieties to a PEG hydrogel. The hybrid network was obtained from the crosslinking reaction of poly(ethylene glycol) diacrylate prepolymer and the SWNT–PEGMA by dual photo-UV and thermal initiations. The mechanical and swelling properties of the new hybrid material were studied. In addition, the material and lixiviates were analyzed to elucidate any kind of SWNT release and to evaluate a possible in vitro cytotoxic effect. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.
Resumo:
Carbon nanotubes (CNTs) have been produced by the tunneling of cobalt nanoparticles in carbon fibers that are derived from electrospun polyacrylonitrile (PAN) fibers. During annealing, the PAN fibers transform to a composite of cobalt nanodroplets and carbon fibers. Driven by the high chemical potential of wrinkled graphene platelets and amorphous carbon with respect to graphite, the cobalt nanodroplets are to tunnel in the carbon fibers. When cobalt nanodroplets have an elongated shape, carbon atoms dissolved in the droplets precipitate preferentially and completely at their lateral sides, producing perfect CNTs that form bulk structures. © 2012 Springer-Verlag Berlin Heidelberg.
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The newly synthesized dioxaborine dyes were studied aiming to probe amines and carbon nanotubes, which are potential toxic industrial polluters. To detect the targeted analytes in efficient way, series of ca. 20 dioxaborine dyes were synthesized and tested for reactivity with amines and carbon nanotubes. The most promising result was showed for styryl dye with the fluorescent sensitivity to amines up to 1 ppm. A fluorescent response of the dioxaborine dyes on presence of carbon nanotubes was revealed.
Resumo:
We study polarization dynamics of a harmonic mode-locked erbium-doped fiber laser with carbon nanotubes absorber. New types of vector solitons are shown for multi-pulse and harmonic mode-locked operation with locked, switching and precessing polarization states. © 2014 OSA.
Resumo:
Carbon nanomaterials are an active frontier of research in current nanotechnology. Single wall Carbon Nanotube (SWNT) is a unique material which has already found several applications in photonics, electronics, sensors and drug delivery. This thesis presents a summary of the author’s research on functionalisation of SWNTs, a study of their optical properties, and potential for an application in laser physics. The first significant result is a breakthrough in controlling the size of SWNT bundles by varying the salt concentrations in N-methyl 2-pyrrolidone (NMP) through a salting out effect. The addition of Sodium iodide leads to self-assembly of CNTs into recognizable bundles. Furthermore, a stable dispersion can be made via addition polyvinylpyrrolidone (PVP) polymer to SWNTs-NMP dispersion, which indicates a promising direction for SWNT bundle engineering in organic solvents. The second set of experiments are concerned with enhancement of photoluminescence (PL), through the formation of novel macromolecular complexes of SWNTs with polymethine dyes with emission from enhanced nanotubes in the range of dye excitation. The effect appears to originate from exciton energy transfer within the solution. Thirdly, SWNT base-saturable absorbers (SA) were developed and applied to mode locking of fibre lasers. SWNT-based SAs were applied in both composite and liquid dispersion forms and achieved stable ultrashort generation at 1000nm, 1550nm, and 1800 nm for Ytterbium, Erbium and Thulium-doped fibre laser respectively. The work presented here demonstrates several innovative approaches for development of rapid functionalised SWNT-based dispersions and composites with potential for application in various photonic devices at low cost.