The effect of covalent functionalization of carbon nanotube reinforcements on the atomic-level mechanical properties of poly-vinyl-ester-epoxy

The effect of covalent functionalization of (5,5)/(10,10)/(15,15) three-wall carbon nanotubes (3WCNTs) on the atomic-level mechanical properties of 3WCNT-reinforced vinyl ester epoxy polymer has been studied using molecular mechanics calculations. Inter- and intra-molecular atomic interactions in the 3WCNT + vinyl ester epoxy polymer system are represented using condensed-phased optimized molecular potential for atomistic simulation studies (COMPASS), an ab initio forcefield that enables an accurate and simultaneous prediction of various gas-phase and condensed-phase properties of organic and inorganic materials. The computational crystal consisting of a periodic array of infinitely long 3WCNTs surrounded by amorphous poly-vinyl-ester-epoxy is constructed using an in-house developed computer program and the amorphous cell tools by Accelrys. All the computations are carried out using Discover, a molecular statics/dynamics program from Accelrys.The results obtained show that covalent functionalization has a profound effect of the matrix-to-nanotube load transfer especially when the loads are applied in a direction orthogonal to the nanotube axis.     

Investigation of the influence factors of polyethylene molecule encapsulated into carbon nanotubes by molecular dynamics simulation

In this work, the influence factors, namely chirality, temperature, radius and surface chemical modification, of the interaction energy for polyethylene (PE) molecule encapsulated into single-walled carbon nanotubes (SWNTs) had been investigated by molecular mechanics (MM) and molecular dynamics (MD) simulation. The results showed that all these factors would influence the interaction energy between PE and SWNTs. The interaction energy between PE molecule and the armchair SWNTs is largest among eight kinds of chiral SWNTs. The interaction energy decreases with the increase of temperature or the SWNT radius. The methyl, phenyl, hydroxyl, carboxyl, -F, and amino groups, have been introduced onto the surface of the SWNTs by the simulation software and the influence of SWNT chemical modification has also been investigated. The interaction energy between PE and chemically modified SWNTs is larger than that between PE and pristine SWNTs, and increases with increasing the concentration of the modified groups monotonously. In addition, the group electronegativity and van der Waals force will affect the interaction energy between PE and chemically modified SWNTs greatly, which can be attributed to the electronic structures of the chemically modified groups. This study can provide some useful suggestions for the composite material design and drug transport.     

Fabrication and structure: a study of aligned carbon nanotube/carbon nanocomposites

Aligned carbon nanotube/carbon (Acnt/C) nanocomposites have been fabricated by densifying an Acnt preform with chemical vapour infiltration technology. Microstructure observations show that pyrocarbon in Acnt/C was mainly rough lamella type while pyrocarbon in carbon fiber reinforced carbon matrix (C/C) composites was typically smooth lamella type in spite of the same process. The thermal conductivity of these Acnt/C nanocomposites is about 4 times that of C/C composites. Their electrical conductivity of Acnt/C nanocomposites was anisotropic, i.e. approximately 1.61×10⁴ Ω⁻¹ m⁻¹ and 5.68×10³ Ω⁻¹ m⁻¹ in the direction parallel and vertical to the aligned carbon nanotubes, respectively.     

On the compressive response of carbon nanotube tangles

The nonlinear bulk compressibility of entangled multiwalled carbon nanotubes is studied. The analogy with textile fibre assemblies is explored by means of the well established van Wyk model. In view of the small diameter of the nanotubes, the possible effect of adhesive van der Waals interactions at tube-tube contacts is analysed. It is found, however, that the contribution of adhesive contacts to the bulk stress should be negligible. Compression experiments are performed on multi-walled carbon nanotubes and show that van Wyk's model is able to describe the response, although the values of the dimensionless parameter k of van Wyk's model were lower than expected. There is indeed no indication that van der Waals interactions play any significant role.     

Y-branching of single walled carbon nanotubes

Y-branching was observed by scanning tunnelling microscopy (STM) in single wall carbon nanotubes grown by thermal decomposition of C₆₀ fullerene in the presence of transition metals. These novel carbon nanostructures may play an important role in carbon-based nanoelectronics. Received: 18 November 1999 / Accepted: 20 January 2000 / Published online: 8 March 2000     

Field emission properties of polymer-converted carbon films by heat treatment

Carbon films were prepared on single crystal silicon substrates by heat-treatment of a polymer-poly(phenylcarbyne) at 800 °C in Ar atmosphere. The heat-treatment caused the change of the polymer into carbon film, which exhibited good field emission properties. Low turn-on emission field of 4.3 V/μm (at 0.1 μA/cm²) and high emission current density of 250 μA/cm² (at 10 V/μm) were observed for the polymer-converted carbon films. This behavior was demonstrated to be mainly related to the microstructure of the carbon films, which consisted of fine carbon nanoparticles with high sp² bonding. The carbon films, which can be deposited simply with large areas, are promising for practical applications in field emission display.     

Dependence of the sp3 bond fraction on the laser wavelength in thin carbon films prepared by pulsed laser deposition

3 bonds in the carbon films prepared by pulsed laser deposition of carbon obtained from graphite was investigated by electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS). The fraction of sp³ bonds increased with a decreasing laser wavelength. Energetic C⁺ ion species were effectively produced by using a short-wavelength laser. The sp³ bond fraction increased with an increasing amount of energetic C⁺ ion species. The fractions of sp³ bonds in the carbon film were 80%, 42%, 26% and 15% at wavelengths of 193, 248, 532 and 1064 nm, respectively. Received: 28 October 1997/Accepted:29 October 1997     

Characterization of ablation plumes and carbon nitride films produced by reactive pulsed laser deposition in the presence of a magnetic field

x ) films in a nitrogen atmosphere within the range 5×10^-4–4×10^-1 Torr. In the presence of a magnetic field, the emission intensities of N₂ (second positive system) and CN species in the graphite ablation plumes were altered significantly, depending on the pressure of the N₂ environment. Corresponding to an intense CN emission, a magnetic field-induced enhancement of N incorporation – for example, up to 37% at an N₂ pressure of 300 mTorr – and the formation of sp³ tetrahedral CN bonding were both observed in the films. This suggests that the arrival of CN species at the substrate surface with kinetic energies is important for film deposition. Received: 27 August 1997/Accepted: 8 September 1997     

STM morphology study of ropes of single-wall carbon nanotubes

Received: 10 February 1998     

Nitrogen-rich carbon nitride materials shock-synthesized from carbon tetrahalide and sodium dicyanoamide

Shock reactions between CX₄ (X=Br or I) and NaN(CN)₂ were investigated to prepare carbon nitrides. The post shock samples were characterized by the powder X-ray diffraction (XRD) technique. The XRD spectrum of the product showed a peak in the range of 0.324-0.336 nm in d-value corresponding to the (002) basal plane diffraction in graphitic structure. Elemental analysis (C, H, N, O) of the product showed that the atomic ratio of nitrogen to carbon (N/C) ranged from 0.38 to 1.3. Analysis of data revealed that the d-value increased and the nitrogen content decreased with the increase of the impact velocity.     

Growth mechanisms for single-wall carbon nanotubes in a laser-ablation process

Mechanisms proposed in the literature are compared with a current scenario for the formation of single-wall carbon nanotubes in the laser-ablation process that is based on our spectral emission and laser-induced fluorescence measurements. It is suggested that the carbon which serves as feedstock for nanotube formation not only comes from the direct ablation of the target, but also from carbon particles suspended in the reaction zone. Fullerenes formed in the reaction zone may be photo-dissociated into C₂ and other low molecular weight species, and also may serve as feedstock for nanotube growth. Confinement of the nanotubes in the reaction zone within the laser beam allows the nanotubes to be ‘purified’ and annealed during the formation process by laser heating. Received: 2 November 2000 / Accepted: 3 November 2000 / Published online: 23 March 2001     

Lower limit for single-wall carbon nanotube diameters from hydrocarbons and fullerenes

A theoretical model for the growth of single-wall carbon nanotubes produced by metal-catalyzed decomposition of hydrocarbons and fullerenes is presented. The growth process is treated as a thermodynamic equilibrium between carbon in the gas phase and carbon in the nanotube. The minimum possible nanotube diameters based on several published experimental conditions are calculated by combining the free energy of the reaction with an equation derived from elastic theory. The model predicts the possibility of generating nanotubes with extremely small diameters that are smaller than in the corresponding experiments. Received: 18 July 2001 / Accepted: 19 November 2001 / Published online: 4 March 2002     

Atomic force microscopy of bamboo-shaped multiwalled carbon nanotube structures

Atomic force microscopy (AFM) was employed for the morphology measurements of bamboo-shaped multiwalled carbon nanotubes (BS-MWNTs) grown by thermal chemical vapor deposition on Fe catalyst deposited SiO₂/Ti substrates. Greater diameters and compartment distances of the bamboo structures were observed for the BS-MWNTs grown at 950 °C than for those grown at 850 °C.     

Electrochemical synthesis of polypyrrole/carbon nanotube nanoscale composites using well-aligned carbon nanotube arrays

Polypyrrole/carbon nanotube nanoscale composites were successfully fabricated by electrochemical deposition of polypyrrole over each of the carbon nanotubes in well-aligned large arrays. The thickness of the polypyrrole coating can be easily controlled by the value of the film-formation charge. For both thin (low film-formation charge) and thick (high film-formation charge) films, the polypyrrole coating on the surface of each nanotube is very uniform throughout the entire length, as observed by transmission electron microscopy. Received: 2 May 2001 / Accepted: 4 May 2001 / Published online: 20 June 2001     

Surface chemical modification of fullerene by mechanochemical treatment

In this study different encapsulating agents have been used for chemical modification of fullerenes. Fullerenes have reacted with tetrahydrofuran, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate and ethylene vinyl acetate-ethylene vinyl versatate at room temperature under mechanical milling. The obtained powder has been dispersed in water by ultrasonication. The fullerene based colloids have been characterized by UV-vis, FTIR, Raman spectroscopy and atomic force microscopy. FTIR and Raman analysis have shown the presence of C₆₀ after surface functionalization.     

In situ electrochemical contact angle study of the biorecognition based on C60DF monolayer interface

In this study, the specific DNA binding behavior of a water soluble C₆₀ derivative (C₆₀DF) and redox-controlled hydrophilic-to-hydrophobic transformations of the relative C₆₀DF monolayer on surfaces of glassy carbon electrode (GCE) have been demonstrated by using in situ electrochemical static contact angle analysis. The results illustrate that in situ electrochemical contact angle detection based on C₆₀DF functional film can be utilized to sensitively probe some specific bio-molecular recognition like DNA interaction, which will provide the new strategy to develop the promising multi-signal responsive biosensors for relevant biological process.     

Chromatographic size separation of single-wall carbon nanotubes

Received: 18 May 1998/Accepted: 22 May 1998     

Spectroscopic properties and STM images of carbon nanotubes

Received: 23 November 1998 / Accepted: 22 December 1998     

New synthesis of multi-walled carbon nanotubes using an arc discharge technique under organic molecular atmospheres

We have synthesized multi-walled carbon nanotubes (MWNTs) using a DC arc discharge method under organic molecular atmospheres. This method allows us to synthesize about five times more MWNTs than are synthesized using the usual arc discharge method, using discharge conditions of 100 A and 20 V. We have examined the synthetic yield of MWNTs at various pressures under different organic atmospheres. The yield of MWNTs increases with the number of carbon atoms in the organic molecule. Received: 21 September 2000 / Accepted: 18 December 2000 / Published online: 26 April 2001     

“Sputtered-atom assembly” of carbon nanostructures during ion bombardment

We report the observation of a carbon nanostructure grown on a graphite surface by Ar⁺ ion bombardment. We demonstrate experimentally that, in view of transmission electron microscopy (TEM)-based evidence, some of these carbon nanostructures emerged the whiskerlike protrusion and/or the sputtered-surface, suggesting a new growth model for nanocarbon, distinctly different from that found in arc-discharge and many other methods. Received: 14 April 2000 / Accepted: 17 April 2000 / Published online: 13 July 2000