Multiple-walled nanotubes

Elemental analysis of chlorinated samples of carbonic nanofibers and multiple wall nanotubes revealed that the abundance of chlorine in compounds obtained is 5,8 and 1,3 mass. %, respectively. 

This involves stating that nanomateiials wiU be specifically examined in future revisions of the directive. Regarding the legislation implemented by the Commission on Environment, Public Health and Food Safety, it is proposed that particular attention will be given to nanosUver and long carbon, multiple-walled nanotubes. 

Both single-walled nanotubes (Figure 8.18) and multiple-walled nanotubes with multiple, concentric layers of carbons have been studied extensively. Commercially they are prepared by a variety of methods, including application of electric arcs to graphite... 

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. 

Since the 1970s, patch-clamp electrodes (electrodes placed inside a borosilicate glass pipet that is then heated and pulled, with its contents, to submicron-size diameters) have been used as micron-sized probes in elec-trophysiology experiments. Since 2000, single-walled and multiple-walled carbon nanotubes have been used as nanoelectrodes. 

Nanotubes. If the ends of the nanotube shown in Figure 8-16 are uncapped, the result is a hollow tube of very small dimension. Such ilanombes have been synthesized both with single and multiple walls (multiple layers built up on the outside of the innermost tube). One of the most promising potential applications of such structures is in the electronics industry. Extensive work has been done to devise methods for constructing computer circuits that use carbon nanotubes, and the nanombes have been cited as the leading candidate to replace silicon when the size limit on miniaturization of silicon chips has been reached. ... 

Single-wall nanotubes retain some of these features, however, in contrast to graphene, they are either metals or semiconductors, depending on the helicity [125,139,141-143]. This property is a consequence of the symmetry [124]. In particular, if (n-m) is a multiple of 3, then the tube is metallic (i.e. will have a non-zero density of states at the Fermi level), otherwise there is a gap between the highest occupied and lowest unoccupied levels. 

Drugs can be sequestered inside the nanotubes and the surface of the tubes can be derivatized (103). Typical dimensions of SWNT are 1 to 3 nm in diameter and 0.5 to 2 pm in length. The inner diameter is from 0.6 to 2.4 nm, and the length of the tubes may vary up to 100 pm. With multiple walls, the separation between the layers is of the order of 0.3 to 0.4 nm. Foldvari and Bagonluri (104) have discussed drug delivery and compatibility issues. The asymmetry of CNTs may have consequences in their biodistribution as well as toxicity. 

Rolf Landauer proved that the minimum resistance of any single-channel wire (composed of atoms or molecules or polymers), measured between any two macroscopic electrodes, is the quantum of resistance R = (h/2e ) = 12.91 kQ, where h is Planck s constant, and e is the electronic charge. In Milestone Two, this Landauer quantum of resistance was measured by Walt de Heer and coworkers at room temperature between a multiple-walled carbon nanotube (MWCNT), glued to a conducting AFM tip, and a pool of liquid... 

Fig. 3.4 Multiple-wall carbon nanotube (CNT) acting as an anchoring support for PVPfOsfbipylJ Cl (Reproduced fiom Ref. [32] with the permission of Elsevier)...

Huang, H.M. Liu, I.C. Chang, C.Y. Tsai, H.C. Hsu, C.H. Tsiang, R.C.C. (2004). Preparing a polystyrene-functionalized multiple-walled carbon nanotubes via covalently linking acyl chloride functionalities with living polystyryllithium. Journal of Polymer Science, Part A Polymer Chemistry, 42, 5802-5810. 

Experiments have shown that capacitance-based gas sensors can detect vapors and gases with concentration in the ppm range. For example, Kitsara et al. (2006) reported on detection limits for PDMS-covered cantilevers below 50 ppm for toluene and 10 ppm for octane. Rodriguez et al. (2004), using frequenqr multiplication and PDMS as the active layer, established that the sensors had sensitivity to concentrations of toluene as low as 25 ppm. For gases the sensitivity is lower. Sivaramakrishnan et al. (2008) found that capacitance-based sensors with membranes coated by a single-walled nanotube (SWNT) film can detect CO with concentrations from 3.2 to 10.4 %. 

At the present time, important nanofillers include certain nanoclays (montmorillonite, hydrotalcite in platelet form), nanofibers (single- and multiple-wall carbon nanotubes), and nanosized particulate metal oxides. Several technological advances will undoubtedly contribute to additional growth in the usage of these fillers. Examples of such advances include [45]... 

It has to be taken into consideration that a great variety of materials is included under the same name. For example, CNTs can be present in different forms and therefore properties and applications could be diverse [144], Apart from variations in diameter or length, two main classes can be distinguished multiple-wall carbon nanotubes (MWCNTs) and... 

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