Nanotubes An Introduction

Carbon nanotubes represent high potential fillers owing to their remarkably attractive mechanical, thermal and electrical properties. The incorporation of nanotubes in the polymer matrices can thus lead to synergistic enhancements in the composite properties even at very low volume fractions. This chapter provides a brief overview of the properties and synthesis methods of nanotubes for the generation of polymer nanocomposites. 

Keywords nanotubes, nanocomposites, electrical, mechanical, vapor deposition, laser, arc. 

The credit for realizing the nanotubes in an arc discharge apparatus is given generally to Iijima who could successfully prove the existence of first multi walled carbon nanotubes (MWCNT) mixed with other forms of carbon (4). He observed a graphitic tubular structure 

The two basis vectors a, and a2 are shown. Folding of the (8,8), (8,0), and (10,-2) vectors leads to armchair (b), zigzag (c), and chiral (d) tubes, respectively. Reproduced from reference 3 with permission from American Chemical Society. 

Reproduced from reference 9 with permission from American Chemical Society. 

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Many body potentials e.g. Sutton-Chen, Tersoff, " Brenner can be used to describe metals and other continuous solids such as silicon and carbon. The Brenner potential has been particularly successful with fullerenes, carbon nanotubes and diamond. Erhart and Albe have derived an analytical potential based on Brenner s work for carbon, silicon and silicon carbide. The Brenner and Tersolf potentials are examples of bond order potentials. These express the local binding energy between any pair of atoms/ions as the sum of a repulsive term and an attractive term that depends on the bond order between the two atoms. Because the bond order depends on the other neighbours of the two atoms, this apparently two-body potential is in fact many-body. An introduction and history of such potentials has recently been given by Finnis in an issue of Progress in Materials Science dedicated to David Pettifor. For a study of solid and liquid MgO Tangney and Scandolo derived a many body potential for ionic systems. 

This book serves as an introduction to advanced inorganic fibers and aims to support fundamental research, assist applied scientists and designers in industry, and facilitate materials science instruction in universities and colleges. Its three main sections deal with fibers which are derived from the vapor phase such as single crystal silicon whiskers or carbon nanotubes, from the liquid phase such as advanced glass and single crystal oxide fibers, and from solid precursor fibers such as carbon and ceramic fibers. 

Ramasubramaniam R, Chen J, Liu H (2003) Homogeneous carbon nanotube/polymer composites for electrical applications. Appl Phys Lett 83 2928 Sahimi M (1994) Applications of percolation theory. Taylor Francis, London Shante VKS, Kirckpatrick S (1971) An introduction to percolation theory. Adv Phys 30 325 Sherman RD, Middleman LM, Jacobs SM (1983) Electron transport processes in conductor-filled polymers. Polym Sci Eng 23 36... 

Of particular importance to carbon nanotube physics are the many possible symmetries or geometries that can be realized on a cylindrical surface in carbon nanotubes without the introduction of strain. For ID systems on a cylindrical surface, translational symmetry with a screw axis could affect the electronic structure and related properties. The exotic electronic properties of ID carbon nanotubes are seen to arise predominately from intralayer interactions, rather than from interlayer interactions between multilayers within a single carbon nanotube or between two different nanotubes. Since the symmetry of a single nanotube is essential for understanding the basic physics of carbon nanotubes, most of this article focuses on the symmetry properties of single layer nanotubes, with a brief discussion also provided for two-layer nanotubes and an ordered array of similar nanotubes. 

Carbon nanotubes inevitably contain defects, whose extent depends on the fabrication method but also on the CNT post-treatments. As already seen, oxidizing treatments, such as acid, plasma or electrochemical, can introduce defects that play an important role in the electrochemical performance of CNT electrodes. For instance, Collins and coworkers have published an interesting way to introduce very controlled functionalization points or defects on individual SWNTs by electrochemical means [96]. Other methodologies to introduce artificial defects comprise argon, hydrogen and electron irradiation. Under this context, a number of recent works have appeared with the goal of tailoring the electrochemical behavior of CNT surfaces by the controlled introduction of defects [97, 98]. 

As already reported by several authors, the addition of carbon nanotubes did not affect the storage modulus in the glassy region, nevertheless a strong increase with the filler content is observed in the rubbery region. In conventional composites, this increase is mainly attributed to interfacial interactions leading to introduction of additional cross-links into the network by the filler. These interfacial interactions contribute to the formation of an adsorption layer whose thickness has been estimated around 2 or 3 nm and where... 

Among carbon-based materials, carbon nanotubes appeared to be the most effective support. The introduction of MWNT into titania matrix obviously creates a kinetic synergetic effect in phenol degradation with an increase in the rate constant by a factor of 2.7. To understand the role of the support in this composite catalyst, a suspended mechanical mixture of 20% MWOT and Ti02 was prepared by merely stirring. As expected, the irradiated mixtures show less synergetic effect than the composite catalyst with the same MWNT content. The calculated R value was of 2.3 (Table 2). 

After single wall nanotubes (SWNT) arise and since there is a large supply of carbon atoms on their surfaces, they change to multiwall nanotubes (MWNT). These are numerous tubes concentrically grown within one another (26), (27), (28). Their diameters are different and as discussed above each of these will possess different electrical properties. This was confirmed by scientists at IBM (29) who by the introduction of a strong electric current can build the consecutive component tubes of a MWNT structure, then starting from the layer on the outside can bum down to a tube with the required band gap. The diameter of a SWNT and the diameter of the innermost tube of a MWNT structure can be very different. Most often this is from a few nanometers to several tens of nanometers. Recently there was an announcement that the narrowest possible nanotube has been obtained. In this case the carbon atoms are arranged in a row. 

Y. F. Huang and C. W. Lin, Introduction of methanol in the formation of polyaniline nanotubes in an acid-free aqueous solution through a self-curling process. Polymer, 50, 775-782 (2009). 

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