Carbon nanotubes alignment control

The primary synthesis methods for single and multi-walled carbon nanotubes include arc-discharge [203, 204], lase ablation [205], gas-phase catalytic growth from carbon monoxide [206], and chemical vapor deposition (CVD) from hydrocarbons [207-209], The scale-up limitation of arc discharge and laser ablation methods would make them cost prohibitive. One unique aspect of CVD technique is its ability to synthesize aligned arrays of carbon nanotubes with controlled diameter and length. The details on these methods go beyond the scope of this chapter. 

The packing density of the self-assembled, aligned carbon nanotubes can be controlled through the incubation time. 

Chaudhary S, Kim JH, Ozkan M (2006). Controlled electron-beam-induced large-scale alignment of carbon nanotubes at metal electrodes. J. Nanoelectron. Optoelection. 1 211-214. 

The field emission properties of carbon nanotube forests and single nanotubes are described. Controlled emission is possible for aligned CNT arrays where the spacing is twice the CNT height, as grown by plasma enhanced chemical vapor deposition. This leads to the maximum field enhancement factor. For random forests, the field enhancement obeys an exponential distribution, leading to a lower emission site density and imperfect current sharing. Ballast resistors can help alleviate this problem. Random nanocarbons perform less well than CNTs. Some applications are covered. Elec-... 

Dieckmann et al. in 2003 described an amphiphilic a-helical peptide specifically designed to coat and solubilize CNTs and to control the assembly of the peptide-coated nanotubes into macromolecular structures through peptide-peptide interactions between adjacent peptide-wrapped nanotubes [227]. They claimed that the peptide folds into an amphiphilic a-helix in the presence of carbon nanotubes and disperses them in aqueous solution by noncovalent interactions with the nanotube surface. EM and polarized Raman studies revealed that the peptide-coated nanotubes assemble into fibers with the nanotubes aligned along the fiber axis. The size and morphology of the fibers could be controlled by manipulating the solution conditions that affect peptide-peptide interactions [227]. 

In summary, the catalytic route provides an interesting way to prepare carbon nanotubes with high yield and selectivity at relatively low synthesis temperature. The easy scale-up of the catalytic method allows one to ensure the mass production of these ID materials with reasonable cost for large scale applications. The development of different methods to produce carbon nanotubes in a controlled macroscopic shape and size, i.e. constraint synthesis, patterned and aligned carbon nanotubes forest by pyrolysis of organic compounds, avoids the formation of fines... 

Zhou, Y., M. Ghaffari, M. Lin et al. 2013. High volumetric electrochemical performance of ultra-high density aligned carbon nanotube supercapacitors with controlled nanomorphology. Electrochimica Acta 111 608-613. 

The fact that the carbon nanotubes can be aligned between the electrodes yields a further degree of control in device formation initial results have indicated that the aligmnent of the SWNTs with respect to the metal electrodes affects overall response. This allows an additional degree of control, or tunability, in device behavior. 

Xiang R, Yang Z, Zhang Q, Luo G, Qian W, Wei F, et al. Growth deceleration of vertically aligned carbon nanotube arrays catalyst deactivation or feedstock diffusion controlled J Phys Chem C 2008 112 4892-6. 

The properties of carbon nanotubes are not only sensitive to their diameter and chirality but are also highly anisotropic. The stiffness, strength and electrical, magnetic and optical properties of the nanotube-reinforced composites strongly depend on the orientations of the nanotubes. Therefore, it is crucial to obtain the controllable alignment of the nanotubes in the nanocomposite. 

Cebeci H, de Villoria R G, Hart A J and Wardle B L (2009) Multifunctional properties of high volume fraction aligned carbon nanotube polymer composites with controlled morphology, Compos Sci Techno 69 2649-2656. 

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