Tensile properties of long aligned double-walled carbon nanotube strands

The mechanical properties of well-aligned double-walled carbon nanotube (DWNT) strands with diameters of 3-20 μm and lengths of ∼10 mm were measured using a stress-strain puller. The average tensile strength and Young’s modulus of the tested strands are 1.2 GPa and 16 GPa, respectively. Deformation and fracture processes of these samples are discussed. The tensile strength and Young’s modulus of an individual DWNT bundle were estimated, with values comparable to those of SWNT bundles. The superior mechanical strengths of our as-prepared DWNT strands are expected to give them potential as a high-strength material and a reinforcement in composites.     

Electronic properties of double-walled carbon nanotube films

The electronic properties of as-prepared and purified DWNT films were tested using the four-probe method. The resistivity of the purified DWNT films is about 1 mΩ cm at room temperature and has a positive dρ/dT above 55 K, which shows a good metallic property. The electrical resistivities of the purified DWNT films are quite similar to those of the SWNT bundles and acid-treated SWNTs. Our results are correspondent with the early theoretical calculation on the band structure of DWNTs.     

Mechanical properties of carbon nanotube paper in ionic liquid and aqueous electrolytes

Porous mats of carbon nanotubes, referred to as bucky paper, are becoming a viable engineering material, especially as electrodes in numerous types of electrochemical cells. The tensile strength of bucky paper was measured in the dry atmospheric condition, and the wet conditions of both water and 1-butyl-3-methyl-imidazolium tetrafluoroborate, an ionic liquid. The two different liquids have a significant impact on the mechanical properties of bucky paper, even when they are not known for readily wetting the nanotubes. It is shown that capillary forces contribute to the mechanical properties of bucky paper. It is also shown that there is a strong interaction between ionic liquid and carbon nanotubes.     

Structure and energetics of carbon nanotube ropes

High-resolution electron microscopy observation and energetic analysis have been performed on ropes formed from single-walled carbon nanotubes. When individual nanotubes are twisted, the nanotube ropes become energetically stable—a configuration that also offers better structural stability. Electron microscopic image simulations of an energetically-stable rope composed of seven single-walled carbon nanotubes have been carried out as well to elaborate the salient features that were observed experimentally.     

Fabrication and electrochemical properties of carbon nanotube film electrodes

Carbon nanotube (CNT) film electrodes were fabricated by a novel process involving the electrostatic spray deposition (ESD) of a CNT solution. Acid treated CNTs were dispersed in an aqueous solvent through sonication and then the CNT solution was electrostatically sprayed onto a metallic substrate by the ESD method. The CNT film electrodes showed well-entangled and interconnected porous structures with good adherence to the substrate. A specific capacitance of 108 F/g was achieved for the electrodes in 1 M H₂SO₄. In addition, the CNT film electrode showed good high rate capability.     

Electronic and optical properties of double-walled armchair carbon nanotubes

Magnetoelectronic structures of double-walled armchair carbon nanotubes are calculated according to the tight-binding model. Their features are dominated by the intertube interactions, the symmetric configurations, the magnetic flux, and the Zeeman splitting. The drastic changes of the low energy states, such as energy dispersion, wave function, and Fermi level, which also rely on the different symmetries, are caused by the intertube interactions. The magnetic flux could change linear bands into parabolic bands, destroy state degeneracy, open an energy gap, and shift Fermi level. The magnetic flux and the intertube interactions, however, compete with each other in the metallic or semiconducting behavior. The Zeeman splitting would suppress the metal–semiconductor transition while the opposite is true of the magnetic flux. The main characteristics of energy bands are directly reflected in the magneto-optical absorption spectra. The different symmetric configurations can be distinguished by the absorption peaks, and the threshold absorption frequency is not identical with the energy gap.     

The thermal and mechanical properties of a polyurethane/multi-walled carbon nanotube composite

A polyurethane/multi-walled carbon nanotube elastomer composite was synthesized. The microstructure of the composite was examined by field-emission scanning electron microscopy and transmission electron microscopy. The thermal and mechanical properties of the composite were characterized by dynamic mechanical thermal analysis, thermogravimetric analysis and tensile testing. The chemical linkage of carbon nanotubes with polyurethane matrix was confirmed by Fourier transform infrared spectra. The study on the structure of the composite showed that carbon nanotubes could be dispersed in the polymer matrix well apart from a few of clusters. The results from thermal analysis indicated that the glass transition temperature of the composite was increased by about 10 °C and its thermal stability was obviously improved, in comparison with pure polyurethane. The investigation on the mechanical properties showed that the modulus and tensile strength could be obviously increased by adding 2 wt% (by weight) CNT to the matrix.     

Small but strong: A review of the mechanical properties of carbon nanotube-polymer composites

The superlative mechanical properties of carbon nanotubes make them the filler material of choice for composite reinforcement. In this paper we review the progress to date in the field of mechanical reinforcement of polymers using nanotubes. Initially, the basics of fibre reinforced composites are introduced and the prerequisites for successful reinforcement discussed. The effectiveness of different processing methods is compared and the state of the art demonstrated. In addition we discuss the levels of reinforcement that have actually been achieved. While the focus will be on enhancement of Young’s modulus we will also discuss enhancement of strength and toughness. Finally we compare and tabulate these results. This leads to a discussion of the most promising processing methods for mechanical reinforcement and the outlook for the future.     

Modeling of effective elastic properties for polymer based carbon nanotube composites

Effective elastic properties of the nanocomposites filled with carbon nanotubes (CNTs) are investigated by the asymptotic expansion homogenization (AEH) method. In order to implement the homogenization method, a control volume finite element method (CVFEM) is employed in contrast to the previous studies. It is assumed that the nanocomposites have geometric periodicity with respect to local length scale and the elastic properties of nanocomposites can be represented by those of the representative volume element (RVE). Random orientation of the CNTs embedded in the nanocomposites is considered by using the orientation tensor. The effective elasticity tensor predicted by the homogenization method is compared with analytical and experimental results. In the experiment, the CNT surface is treated by oxygen plasma to improve interfacial bonding between the CNT and the matrix and to disperse the CNTs homogeneously in epoxy resin because the perfect interfacial bonding is presumed in the homogenization method. Homogeneous CNT dispersion is experimentally identified by the field emission scanning electronic microscope (FESEM). It is found that the numerically calculated elastic modulus is in good agreement with that obtained by analytic model.     

Morphology and tensile properties of unreinforced and short carbon fibre reinforced Nylon 6/multiwalled carbon nanotube-composites

The morphology and the tensile properties of unreinforced and short carbon fibre (SCF) reinforced Nylon 6/multiwalled carbon nanotube (MWCNT)-composites are investigated. The morphology analysis shows that MWCNT and SCF are randomly oriented in the composites. Furthermore, the SCF fail due to fibre pull-out, while the MWCNT fail due to fracture. Young's modulus and tensile strength of SCF reinforced Nylon 6 and Nylon 6/MWCNT-composites increase with increasing total filler volume content. Replacing SCF by MWCNT further enhances Young's modulus and the tensile strength. An additive modelling approach leads to better results at low MWCNT-volume contents, while at higher MWCNT loadings a multiplicative modelling approach results in a better approximation of the experimental data. Thus the SCF reinforced Nylon 6/MWCNT-composites behave at low MWCNT-volume contents like a polymer composite containing two different types of fillers, while at higher MWCNT loadings a behaviour of a short fibre reinforced nanocomposite is observed.     

Effect of H2O adsorption on the electrical transport properties of double-walled carbon nanotubes

Water molecules adsorbed on a double-walled carbon nanotube (DWCNT) serve as charge trapping centers when present in low density and as electron donors when present in high density. There is a discontinuous change between the low- and high-density regions. H₂O molecules are apt to be adsorbed on the outer surface of DWCNTs, and in this case the electrical transport properties are extremely sensitive to environment, which suggests that DWCNTs are hole doped and act as an electric dipole with the inner tube.     

Micropatterning of single-walled carbon nanotube forest

In this work, high-aligned single-walled carbon nanotube (SWCNT) forest have been grown using a high-density plasma chemical vapor deposition technique (at room temperature) and patterned into micro-structures by photolithographic techniques, that are commonly used for silicon integrated circuit fabrication. The SWCNTs were obtained using pure methane plasma and iron as precursor material (seed). For the growth carbon SWCNT forest the process pressure was 15 mTorr, the RF power was 250 W and the total time of the deposition process was 3 h. The micropatterning processes of the SWCNT forest included conventional photolithography and magnetron sputtering for growing an iron layer (precursor material). In this situation, the iron layer is patterned and high-aligned SWCNTs are grown in the where iron is present, and DLC is formed in the regions where the iron precursor is not present. The results can be proven by Scanning Electronic Microscopy and Raman Spectroscopy. Thus, it is possible to fabricate SWCNT forest-based electronic and optoelectronic devices.     

Mechanical properties of carbon nanotubes: a fiber digest for beginners

A condensed review of mechanical properties of carbon nanotubes is given. Theory as well as experiments is examined with a view to extracting the fundamental elements that should allow the reader to build his own perspective of the subject.     

Melt processing and mechanical property characterization of multi-walled carbon nanotube/high density polyethylene (MWNT/HDPE) composite films

High density polyethylene (HDPE) was used as the matrix material for a carbon nanotube (CNT) polymer composites. This combination of composite constituents has not been previously reported in the literature. Multi-wall carbon nanotube (MWNT)/HDPE composite films were fabricated using the melt processing method. The composite films with 0, 1, 3 and 5% nanotube content by weight were analyzed under SEM and TEM to observe nanotube dispersion. The mechanical properties of the films were measured by small punch test. Results show increases in the stiffness, peak load and work to failure for the composite films with increasing MWNT content.     

Microstructure and mechanical properties of hot-pressed carbon nanotubes compacted by spark plasma sintering

Bulk carbon nanotube samples were prepared by spark plasma sintering. The as-prepared bulk carbon nanotube material exhibited brittle fracture similar to that of common ceramics. Its fracture toughness was around 4.2 MPa m^1/2 while flexural strength was 50 MPa due to the weak bonding between carbon nanotubes. Obvious carbon nanotube bridging was found during the development of the crack induced by an indenter, which provides a possibility of carbon nanotube tough material.