Chirality of nanotubes

The question about functionalization of CNTs in nature has a close connection with their bio-application. Functionalization is closely associated with the ability to disperse and perhaps dissolve the nanotubes, which would greatly improve processability.21,22 Due to the fact that the majority of popular synthetic methods produce samples yielding a mixture of many different diameters and chiralities of nanotubes, post-synthesis chemical processing protocols23 are the most popular among the methods of chemical modification. 

According to the rolling angle of the graphene sheet, CNT have three chiralities armchair, zigzag, and chiral one. The chirality of nanotubes has significant impact on their electronic properties (Ma et al. 2010). 

Early transport measurements on individual multi-wall nanotubes [187] were carried out on nanotubes with too large an outer diameter to be sensitive to ID quantum effects. Furthermore, contributions from the inner constituent shells which may not make electrical contact with the current source complicate the interpretation of the transport results, and in some cases the measurements were not made at low enough temperatures to be sensitive to 1D effects. Early transport measurements on multiple ropes (arrays) of single-wall armchair carbon nanotubes [188], addressed general issues such as the temperature dependence of the resistivity of nanotube bundles, each containing many single-wall nanotubes with a distribution of diameters d/ and chiral angles 6. Their results confirmed the theoretical prediction that many of the individual nanotubes are metallic. 

They developed a continuum elastic-free energy model that suggests these observations can be explained as a first-order mechanical phase transition. In other recent work on steroids, Terech and co-workers reported the formation of nanotubes in single-component solutions of the elementary bile steroid derivative lithocholic acid, at alkaline pH,164 although these tubules do not show any chiral markings indicating helical aggregation. 

Carbon nanotubes can have one, two, or many sidewalls and are referred to as single-, double-, or multi-walled nanotubes (SWNT, DWNT, or MWNT). Nanotubes can be metallic, or semi-conducting depending on the chirality of the tube. Single-walled nanotubes (SWNT) are about 1 nm in diameter, and hundreds of nanometers long, whereas multi-walled nanotubes (MWNT) are like nested... 

Bandow S, Asaka S, Saito Y, Rao AM, Grigorian L, Richter E, Eklund PC (1998) Effect of the growth temperature on the diameter distribution and chirality of single-wall carbon nanotubes. Physical Review Letters 80 3779-3782. 

Without doubt, the advent of carbon nanotubes has opened up iimovative perspectives for research and development of carbon electrodes. In this chapter, we have attempted to highlight the electrochemical properties of carbon nanotubes by rooting them mainly on their structural, electronic and chemical properties. If chirality of SWNTs could be controlled, it would be possible to probe electrochemically the unique electronic properties of the tubes with their corresponding unique DOS distribution and establish direct correlations between electronic structure and electrochemistry. However, so far, most of their electrochemical applications are based on ensembles of CNTs (MWNTs or SWNTs) in thin films supported on conductive surfaces or composites. Such ensembles, not so well defined from the structural point of view, contain a mixture of tubes with different diameters and DOS... 

Zheng M, Semke ED (2007) Enrichment of single chirality carbon nanotubes. J Am Chem Soc 129 6084-6085... 

In order to create nanotube based devices, researchers must carefully tailor their electronic properties. This is difficult to achieve as described above since these properties depend on the diameter and chirality of the... 

A molecular dynamics simulation in conjunction with experimental evidence was used to elucidate the nature of the interactions between polymer materials and CNTs [239]. Computational time was reduced by representing CNTs as a force field. The calculations indicated an extremely strong noncovalent binding energy. Furthermore, the correlation between the chirality of the nanotubes and mapping of the polymer on to the lattice was discussed [239]. 

The SWNT systems chosen in the present studies include 3 armchair nanotubes and 3 zigzag nanotubes with diameters ranging from 4 A to 12 A, and 1 chiral nanotube with a diameter of 8.28 A. The nanotubes were carefully chosen to address the fundamental issues of curvature and chirality and the effect of each on the adsorption capacity. First, to understand the curvature effect on hydrogen uptake, we selected nanotubes with diameters varying from about 4 A to 12 A. Next, to investigate the effect of nanotube chirality, we intentionally chose the nanotubes of different chiral architectures with similar diameters. Finally, to study the capacity of a given nanotube, we included three different H2 loadings at 0.4 wt. %, 3.0 wt. % and 6.5 wt. %, respectively, in our MD simulations. 

Jiang J, Dong J, Xing DY (1999) Size and helical symmetry effects on the nonlinear optical properties of chiral carbon nanotubes. Phys. Rev. B 59 9838—9841... 

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