Carbon nanotube orientation

Vadi, M. and E. Ghaseminejhad, comparative study of isotherms adsorption of oleic acid by activated carbon and multi-wall carbon nanotube. Oriental J. Chem. 2011, 27(3), 973. 

It has been established that electrospinning a polymer solution containing well-dispersed carbon nanotubes leads to nanocomposite fibers with the embedded carbon nanotubes oriented parallel to the nanofiber axis due to the large shear forces in a fast fiber-drawing process. Table 1 lists most of the polymer/CNT composite nanofibers produced by electrospining, along with their fiber diameters and tensile properties. 

The nanoscale morphologies formed by spontaneous or induced self-assembly of segmented copolymers exist below a certain critical temperature. The morphologies are reversibly formed. When a morphology with a cylindrical domain is selected as precursor, the product is made of carbon nanotubes. Oriented nanostructures can be formed. The thickness of the film used to affect the process affects the length of the cylinder. Spinning or extrusion of the polymer at the surface prior to carbonization leads to nanowires used in nanoelectronics after pyrolysis. Nanotubes, nanowires, and nanofibers can be formed in this manner. 

Inspired by experimental observations on bundles of carbon nanotubes, calculations of the electronic structure have also been carried out on arrays of (6,6) armchair nanotubes to determine the crystalline structure of the arrays, the relative orientation of adjacent nanotubes, and the optimal spacing between them. Figure 5 shows one tetragonal and two hexagonal arrays that were considered, with space group symmetries P42/mmc P6/mmni Dh,), and P6/mcc... 

Vigolo, B., Penicaud, A., Coulon, C., Sauder, C., Pailler, R., Journet, C., Bernier, P. and Poulin, P. (2000) Macroscopic fibers and ribbons of oriented carbon nanotubes. Science, 290, 1331-1334. 

Fischer, J. E., Zhou, W., Vavro, J., Llaguno, M. C., Guthy, C HaggenmueDer, R., Casavant, M. J., Walters, D. E. and Smalley R. E. (2003) Magnetically aligned single wall carbon nanotube films Preferred orientation and anisotropic transport properties./. Appl. Phys., 93, 2157-2163. 

Yonemura, H., Yamamoto, Y, Yamada, S., Fujiwara, Y. and Tanimoto, Y. (2008) Magnetic orientation of single-walled carbon nanotubes or their composites using polymer wrapping. Sci. Technol. Adv. Mater., 9 (024213), 1-6. 

B.A. Bhattacharyya, V.T. Sreekumar, T. Lui, S. Kumar, M.L. Ericson, H.R. Hauge, and E.R. Smalley, Crystallization and orientation studies in polypropylene/single wall carbon nanotube composite. Polymer 44, 2373—2377 (2003). 

The structure of carbon nanotubes depends upon the orientation of the hexagons in the cylinder with respect to the tubule axis. The limiting orientations are zigzag and arm chair forms, Fig. 8B. In between there are a number of chiral forms in which the carbon hexagons are oriented along a screw axis, Fig. 8B. The formal topology of these nanotube structures has been described [89]. Carbon nanotubes have attracted a lot of interest because they are essentially onedimensional periodic structures with electronic properties (metallic or semiconducting) that depend upon their diameter and chirality [90,91]. (Note. After this section was written a book devoted to carbon nanotubes has been published [92], see also [58].)... 

Stoffelbach, F., et al., An easy and economically viable route for the decoration of carbon nanotubes by magnetite nanoparticles, and their orientation in a magnetic field. Chemical Communications, 2005(36) p. 4532-4533. 

Fig. 13.3 Equipotentials around various arrays of carbon nanotubes (a) Field enhancement at an array of widely spaced nanotube emitters, (b) closely spaced emitters, showing the field screening, (c) field screening at a randomly oriented nanotube forest.

As reported elsewhere [22], similar to those found on other catalysts, the forms of carbon materials deposited on Fe-loading zeolite molecular sieves are carbon nanotube, carbon nanofiber and amorphous carbon. One obvious phenomenon of the carbon nanotubes formed on Fe/NaY or Fe/SiHMS catalysts is that almost all tips of these tubes are open, indicating the interaction between catalyst particles and supports is strong [23]. On the other hand, the optimal formation time of carbon nanotubes on Fe/SiHMS is longer than that on Fe/NaY. However, the size of carbon nanotubes is easily adjusted and the growth direction of carbon nanotubes on the former is more oriented than on the latter. 

Three examples of particular structures of SWCNTs, depending on the orientation of the hexagons related to the tube axis, (a) armchair-type tube (0 = 30°), (b) zigzag type tube (0 - 0°), and chiral tube (0 < 0 < 30°). Reprint from Carbon, vol. 33, No. 7, Dresselhaus M.S., Dresselhaus G., Saito R., Physics of carbon nanotubes, pages 883-891, Copyright (1995) with permission from Elsevier. 

T.C. Dinadayalane, J. Leszczynski, Stone-Wales defects with two different orientations in (5, 5) single-walled carbon nanotubes A theoretical study. Chem. Phys. Lett. 434, 86 (2007)... 

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