ANALYSIS OF MATERIAL MECHANICAL PROPERTIES FOR SINGLE-WALLED CARBON NANOTUBES

Abstract The carbon-carbon bond between two nearest-neighboring atoms is modeled as a beam and the single-walled carbon nanotubes are treated as the space frame structures in order to analyze the mechanical properties of carbon nanotubes. Based on the theory of TersoffBrenner force field, the energy relationships between the carbon-carbon bond and the beam model are obtained, and the stiffness parameters of the beam are determined. By applying the presentmodel, the Young‘s moduli of the single-walled carbon nanotubes with different tube diameters are determined. And the present results are compared with available data.     

‘Hierarchical self-assembly’ of helical amylose/SWNTs complex

Helical amylose/SWNTs complexes (A/S-C) of various sizes, a single nanotube wrapped by amylose in particular, were demonstrated. The formation process of the helical A/S-C was further explained by a novel hierarchical self-assembly model, including the wrapping of amylose chains around SWNT and the hierarchical self-assembly of wrapped-SWNTs into the superstructural A/S-C. Besides the hydrophobic interaction, the hydrogen bonding also plays a certain role in the self-assembly process.     

Electronic Structures of O2 Molecules Chemisorbed on a（8,0） SWNT with Different Oxygen Contents：A Density Functional Theory Study

We report a theoretical study on the electronic structures of O2 chemisorbed on a(8,0) SWNT with different oxygen contents of 6.25,12.5 and 25%,respectively.On the basis of DFT calculations,we find that eight O2 molecules chemisorbed on the(8,0) SWNT aligned in the middle row of the circumference of the tube in proportional spacing way,is seen to become metallic,and a significant increase in conductivity is expected.There are different electronic structures of the functionalized systems related to different oxygen contents or O2 molecules' chemisorbed positions.     

AC and DC percolative conductivity of single wall carbon nanotube polymer composites

The equations needed to correctly interpret both AC and DC conductivity results of single wall carbon nanotube (SWNT) polymer composites and the scaling of these results onto a single master curve are presented. Brief discussions on the factors that determine the critical volume fraction (?_c) and the percolation exponent (t) are also given. The results for a series of SWNT–polyimide composites are presented and the parameters obtained from fitting these results are discussed. The critical volume fraction for electrical percolation of the present composite was about 0.0005. Results obtained from previous work on SWNT (MWNT)–polymer composites and other percolation systems and the modeling (interpretation) of these results are also discussed and compared. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3273–3287, 2005     

The HSAB principle as a means to interpret the reactivity of carbon nanotubes

Polycyclic curved aromatic fragments (C₂₄H₁₂) have been employed as models of the single-walled carbon nanotubes (n,0), where n varies from 4 up to 30. Those structures were chosen on the basis of the analysis of the strain energy values calculated for the models possessing various sizes. The flat coronene structure has been chosen as a molecular fragment topologically resembling the honeycomb lattice in order to investigate the relation between the curvature and reactivity of the sidewalls of SWNTs. In the current study we took into account the interaction of CO and NH₂ (treated as probe molecules) with the exterior surface of nanotubes. Obtained results illustrate that both total as well as local hardness and/or molecular electrostatic potential (MEP) can be a good measure for the reactivity if the influence of geometrical changes is considered. The systematic theoretical studies also show that the calculated interaction energies of sorbed CO on those models are related to the both types of hardness. On the other hand, in the case of amidogen sorbed on the nanotube surface the correlation between the binding energy and MEP is visible. Those differences can be explained by various kinds of the adsorption mechanism, i.e. physical or chemical adsorption, respectively.     

Large‐Scale Production of Homogeneous Helical Amylose/SWNTs Complexes with Good Biocompatibility

The key to developing novel applications of SWNTs in biotechnology and biomedicine is to improve their biocompatibility and solubility in water and to assemble them into useful architectures. We describe how amylose can help to solubilize SWNTs and wrap around SWNTs into helical superstructures with periodic pitch. FT‐IR, Raman spectroscopy, ¹H NMR and HR‐TEM are used to confirm the generation of amylose/SWNTs complexes (A/S‐C). It is demonstrated that most of the A/S‐C have similar diameters (ca. 20–30 nm) and a helical morphology with a pitch of ca. 14 nm. A test of Hela cell viability revealed that the A/S‐C had much better biocompatibility than SWNTs.

     

Preparation and physical/electrochemical characterization of carbon nanotube-chitosan modified pencil graphite electrode

In this work, preparation and characterization of single-walled carbon nanotube-chitosan (SWNT-chitosan) modified disposable pencil graphite electrode (PGE) was carried out. Firstly, commercial single-walled carbon nanotube was purified and characterized using thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDX) for this purpose. Purified SWNT was mixed with chitosan polymer for preparing their composite. Then, PGE was modified with this composite. The characterization of the modified electrode was carried out using atomic force microscopy (AFM). The electrochemical behaviour of the obtained electrode was investigated and compared with the electrochemical behaviour of chitosan modified and unmodified PGEs using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and alternative current (AC) impedance spectroscopy. In order to obtain more sensitive electrochemical signals, the effect of SWNT concentration was studied. This modified electrode also showed electrocatalytic effect for hydrogen evolution.     

Direct Electrochemistry of Catalase at a Gold Electrode Modified with Single‐Wall Carbon Nanotubes

The direct electrochemistry of catalase (Ct) was accomplished at a gold electrode modified with single‐wall carbon nanotubes (SWNTs). A pair of well‐defined redox peaks was obtained for Ct with the reduction peak potential at ?0.414 V and a peak potential separation of 32 mV at pH 5.9. Both reflectance FT‐IR spectra and the dependence of the reduction peak current on the scan rate revealed that Ct adsorbed onto the SWNT surfaces. The redox wave corresponds to the Fe(III)/Fe(II) redox center of the heme group of the Ct adsorbate. Compared to other types of carbonaceous electrode materials (e.g., graphite and carbon soot), the electron transfer rate of Ct redox reaction was greatly enhanced at the SWNT‐modified electrode. The peak current was found to increase linearly with the Ct concentration in the range of 8×10^?6–8×10^?5 M used for the electrode preparation and the peak potential was shown to be pH dependent. The catalytic activity of Ct adsorbates at the SWNTs appears to be retained, as the addition of H₂O₂ produced a characteristic catalytic redox wave. This work demonstrates that direct electrochemistry of redox‐active biomacromolecules such as metalloenzymes can be improved through the use of carbon nanotubes.     

Atomic Force Microscopic and Electrochemical Investigations of an Electrostatically Fabricated Single‐Wall Carbon Nanotubes Modified Electrode

Single‐wall carbon nanotubes (SWNTs) sub‐monolayer film has been prepared by simply electrostatically adsorbing nanotubes onto a 2‐aminoethanethiol self‐assembled monolayer (SAM) on a gold bead electrode. Tapping‐mode atomic force microscopy (TM‐AFM) is used to characterize the SWNT film, which exhibits that the orientation of SWNTs on the SAM is horizontal and the surface coverage is quite low. The SWNTs modified electrode shows nearly ideal electrochemical response to Fe(CN) /Fe(CN) redox probe. The electrode with such a low SWNTs coverage, however, shows good electrocatalytic behavior to cytochrome c.     

A Semiempirical Study of Carbon Nanotubes with Finite Tubular Length and Various Tubular Diameters

A semiempirical PM3 quantum computational method has been used to generate the electronic and optimized geometrical structure of SWNT of zigzag and armchair types. We shed light on the electronic structures of SWNT with various diameters and lengths of the tube. Particularly, the calculated HOMO, LUMO and band‐gap of SWNT are not monotonic but exhibit a well‐defined oscillation, which depends on the tubular diameter and the tubular length. Calculated HOMO, LUMO and band‐gap of the zigzag SWNTs have oscillated with tubular diameter as they contain an odd or even number of benzenoids in the circular plane of the carbon nanotube. The zigzag SWNTs with an odd number of benzenoids have a higher band‐gap than those of SWNTs with an even number of benzenoids in the circular plane of the carbon nanotube. Calculated results also reveal that the tubular length in the zigzag SWNTs influences the band‐gaps very little. For the armchair SWNT, calculated HOMO, LUMO and band‐gap contained the oscillate depending on the number of carbon sections in the tubular length axis. Their repeat sections are 3n‐1, 3n and 3n+1. The armchair SWNT with 3n+1 sections has a high band‐gap while the SWNTs with 3n‐1 sections have a low band‐gap. The tubular diameters of armchair SWNT influence the HOMO, LUMO and band gap very little.