Carbon nanotubes definition

Chemists have been working for a long time with particles having sizes of nanometers. The novelty of recent developments concerns the ability to make nanostructured substances with uniform particle sizes and in regular arrays. In this way it becomes feasible to produce materials that have definite and reproducible properties that depend on the particle size. The development began with the discovery of carbon nanotubes by Ijima in 1991 (Fig. 11.15, p. 116). 

As the analytical, synthetic, and physical characterization techniques of the chemical sciences have advanced, the scale of material control moves to smaller sizes. Nanoscience is the examination of objects—particles, liquid droplets, crystals, fibers—with sizes that are larger than molecules but smaller than structures commonly prepared by photolithographic microfabrication. The definition of nanomaterials is neither sharp nor easy, nor need it be. Single molecules can be considered components of nanosystems (and are considered as such in fields such as molecular electronics and molecular motors). So can objects that have dimensions of >100 nm, even though such objects can be fabricated—albeit with substantial technical difficulty—by photolithography. We will define (somewhat arbitrarily) nanoscience as the study of the preparation, characterization, and use of substances having dimensions in the range of 1 to 100 nm. Many types of chemical systems, such as self-assembled monolayers (with only one dimension small) or carbon nanotubes (buckytubes) (with two dimensions small), are considered nanosystems. 

If you stick to the definition of an allotrope being a modification of an element characterized by its x-ray crystal structure. Otherwise carbon may have more modifications, when counting all the different fullerenes and carbon nanotubes as allotropes. 

Thermal ablation using carbon nanotubes is a definite option for use in oncology, especially since nanotubes can be functionalized with targeting modalities like folic acid. Some cancer cell types express large numbers of folic acid receptors on... 

CNTs may consist of just one layer (i.e. single-walled carbon nanotubes, SWCNTs), two layers (DWCNTs) or many layers (MWCNTs) and per definition exhibit diameters in the range of 0.7 < d < 2 nm, 1 < d < 3 nm, and 1. 4 < d < 150 nm, respectively. The length of CNTs depends on the synthesis technique used (Section 1.1.4) and can vary from a few microns to a current world record of a few cm [16]. This amounts to aspect ratios (i.e. length/diameter) of up to 107, which are considerably larger than those of high-performance polyethylene (PE, Dyneema). The aspect ratio is a crucial parameter, since it affects, for example, the electrical and mechanical properties of CNT-containing nanocomposites. 

Figure 7.5 shows, for the same period, the relative number of recent patents per fibre type. Nanotubes and nanocomposites, particularly carbon nanotubes, are generating intense research activity whereas research is definitely weaker for nanofibres. Figure 7.6 shows, for the same period, the recent patents for the different nano-reinforcements. 

Generation of the chiral (8,4) carbon nanotube by rolling a graphite sheet along the vector C = naj + ma2, and definition of the chiral angle 9. The reference unit vectors aj and a2 are shown, and the broken lines indicate the directions for generating achiral zigzag and armchair nanotubes. 

Nintendo releases the hand-held gaming system, Nintendo DS Carbon nanotubes are synthesized in bulk, and spun into a yarn iPod Nano and a video-capable iPod are introduced by Apple Motorola releases the ROKR El phone, capable of music downloading High-definition DVD players become commercially available Apple computer introduces MacBook Pro, MacBook, and iMac product lines that contain Intel dual-core chips - the first to contain over one biUion transistors... 

Figure 3.2 (a) Different types of carbon nanotubes result from formal rolling up of a graphene layer, (b) definition of the descriptors n and m and the parameter space,... 

There is yet another phenomenon that points to a 1,4-addition of fluorine atoms occurring at least partially The products obtained from the reaction of single-walled carbon nanotubes with fluorine are definite nonconductors (resistance >20 MQ), while the nanotubes employed feature a resistance of 10-15 2 only. Considering the structures that result from a consecutive 1,2- or 1,4-addition of fluorine, respectively, reveals that an electric current via conjugated it-bonds would still be possible in the 1,2-adduct (Figure 3.70). In the 1,4-adduct, on the other... 

These nanomaterials are also characterized by their extremely high aspect ratio. The aspect ratio is defined as the length of the major axis divided by the width or diameter of the minor axis. According to this definition, spheres have an aspect ratio of 1, while carbon nanotubes or nanofibers have an aspect raho ranging from... 

Although considerable further work is required before any new drugs based on carbon nanotubes are developed, it is hoped that it will eventually lead to more effective treatments for eaneer. However, it is too early to claim whether carbon-based nanomaterials will beeome clinically viable tools to combat cancer, although there is definitely room for them to eomplement existing technologies. 

Although carbon nanotubes (CNTs) have been recently discovered [9], they have been attracting a great deal of scientific interest due to their potential application in areas such as adsorbents and composite materials. CNTs have die number of graphite sheets in tube walls can vary from 1 for single-walled nanotubes (SWNTs) to over SO for multi-walled nanotubes (MWNTs), and inner diameter raging from Inm to Snm with a definite diameter [1,3]. The possibility of controllable pore size and distribution sug sts that CNTs mi t be used applications such as gas storage and selective separations from gas mixtures. 

The above discussion provides summary of QSPR/QSAR approaches applied to classical, chemical compounds. However, an analysis devoted to nanomaterials having gigantic and complex molecular architecture lead to necessity of definition of new approaches for the predictive modelling, because the representation of their molecular structure by means of molecular graph and/or SMILES sometimes becomes very problematic (e.g. multi-walled carbon nanotubes [34], graphene [35]). In the first approximation, the optimal descriptors for such species should be a collector of all available data which are able to impact the physicochemical and/or biochemical behavior of nanomaterials. This concept is displayed in Fig. 12.6. 

Figure 1.12 Three types of carbon nanotubes (a) armchair, (b) zigzag, and (c) chiral. The definition of nanotube types is according to the orientation perpendicular to the nanotube axis. (Figure from Ref. [82].)...

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