Nanotubes fabrication processes

Figure 13.10 Schematic illustration of nanotube fabrication processes (a) nonwoven and (b) quasi-aligned ZnO nanotube structures obtained by a guiding electric field via Al wires, (c) SEM images of as-spun PVAc templates with nonaligned and quasi-aligned...

The most important materials developed are nanocomposites and nanotubes. Fabrication of the first nanocomposites was inspired by nature (biomineralisation). Nanocomposites based on nanoclays and plastics are seen as ideal materials for improved barrier properties against oxygen, water, carbon dioxide and volatiles [37]. This makes them in particular suitable for retaining flavours in foods. The technology is rather straightforward using commercially available nanoclays and extrusion processing. 

Figure 7.17 Nanotubes fabricated by letting a precursor film of polystyrol enter the cylindrical pores of filter [288], A schematic of the two main steps in the fabrication process (left) and a scanning electron microscope image (right) are shown. Thanks to M. Steinhard for providing us with the picture.

Fabrication methods have overwhelmingly focused on improving nanotube dispersion because better nanotube dispersion in polyurethane matrix has been found to improve the properties of the nanocomposites. The dispersion extent of CNTs in the polyurethane matrix plays an important role in the properties of the polymer nanocomposites. Similar to the case of nanotube/solvent suspensions, pristine nanotubes have not yet been shown to be soluble in polymers, illustrating the extreme difficulty of overcoming the inherent thermodynamic drive of nanotubes to bundle. Therefore, CNTs need to be surface modified before the composite fabrication process to improve the load transfer from the polyurethane matrix to the nanotubes. Usually, the polyurethane/CNT nanocomposites can be fabricated by using four techniques melt-mixing (15), solution casting (16-18), in-situ polymerization (19-21), and sol gel process (22). 

A method for preparing conducting polymer nanotubes that can be used for precisely controlled dmg release was reported by Abidian et al. [80]. The fabrication process... 

SWNT/polymer composites could also be made by a two-step fabrication process. For example, SWNT films were first fabricated on glass slides via Mayer rod coating, and then polymers such as PVA, Nafion and polyvinylidenefluoride (PVDF) were infiltrated into SWNT networks. As the polymer occupied the empty space between the nanotubes, a freestanding... 

Because of the potential market size, the possibility of utilizing carbon nanotubes as cold cathode materials for field emission displays has attracted considerable commercial interest. Several major display companies have devoted substantial R D effort in this area. A prototype 9-inch field emission display based on carbon nanotubes has recently been demonstrated. Compared to the lithography-based Spindt-type emitters, the fabrication process can be simplified significantly by using carbon nanotubes as the cold cathodes. However, engineering issues such as emission uniformity and stability have yet to be solved. 

The electrochemical performances of self-organized Ti02 nanotube obtained from Ti foils (references [26, 28] provide examples of the fabrication process) and Ti thin films deposited onto Si substrates have been examined according to a procedure described in reference [34]. Layers of nanotubular titania (ntTi02) are directly produced by the anodization of Ti in fluoride-containing medium and without the use of any template. We... 

The fabrication process for metal silicate nanotubes is depicted in Fig. 32A. HRTEM image of the as-prepared SNT template (Fig. 32B) showed its hollow structure and hierarchical pore structure mesopores at the wall with about a 30 nm thickness and macropores at the center. This hierarchical pore structure is veiy suitable to prepare silicate materials. Under hydrothermal conditions, metal ions and other ions in water solution could easily diffuse into the pores of the SNT template and react with silica species to form metal silicates in situ (Fig. 32C). The original silica mesopores, where the reaction occurs, are uniformly dispersed in the walls, and the metal ions in water solution could easily diffuse into the pores of the SNT template. The whole silica wall with about 30 nm thickness can be readily converted to metal silicates under the reaction conditions. 

This chapter begins by briefly describing the processing techniques used to synthesize the nanostructures including carbon nanotubes, carbon nanofibers and nanowires. Next, the methods by which Pt nanoparticles can be deposited onto the nanostmctures will be examined along with the surface functionalization of these nanostructures. This is followed by a review of fabrication processes of MEA fuel cells containing nanostructures. Finally, we give a summary of the stability of the nanostructure-based fuel cell electrodes. 

Fig. 8.4 CNT nanocomposite membrane process, (a) Schematic membrane fabrication process. Step h The functionalized CNTs are dispersed in THF solution. Step 2 The CNTs/THF solution is filtered through 0.2 pm pore size hydrophobic polytetrafluoroethylene (PTFE) membrane filter. Step 3 The CNTs/PTFE membrane is spin coated with a dilute PS solution. Some nanotube tips are embedded in polymer matrix, (b) Side-view SEM image of CNTs standing vertically on a membrane filter, (c) Side-view SEM image of aligned nanotube/PS nanocomposite membrane after spin-coating. Polymer coating is so thin that some CNT tips are exposed on top of the surface, (d) Side-view SEM image of aligned nanotube/PS/PDMS composite membrane with a protective PDMS coating of 4 pm. (From [8])...

Fig. 13 Fabrication process for hollow conductive polymer nanotubes on a neural probe. The neural probe (A) is coated with biodegradable polymer nanofibers (PLLA) through an electrospinning process (B). Conductive polymers are electrochemically deposited around the nanofibers (C). Since they nucleate at the electrode sites, hollow conducting polymer nanotubes remain on the electrodes (D) after the core material is removed [93]...

The diverse characteristics of nanocomposites, such as thermal, electrical, electrochemical, and mechanical properties, stem from the appropriate selection of fabrication process conditions and material type/formulations. Apparendy, the properties of prepared nanocomposites are much different from those of pure polymers simply because interactions between diverse types of polymers and nanopardcles take place at a molecular level (Matusik et al., 2011). Halloysite nanotubes (HNTs) as the alternative of carbon nanotubes, due to their similar hollow tubular structures, have been... 

Lee KM, Hu CW, Chen HW, Ho KC (2008) Incorporating carbon nanotube in a low-temperature fabrication process for dye-sensitized Ti02 solar ceUs. Sol Energy Mater Sol CeUs 92(12) 1628-1633... 

Lee, C., Park, J. - Growth and structure of carbon nanotubes produced by thermal chemical vapor deposition . Carbon 39 (2001) 1891-1896 Grujicic, M., Cao, G., Gersten, B. - Optimization of chemical vapor deposition process for carbon nanotubes fabrication , Appl. Surface Sci. 191 (2002) 223-239 Bonard, J., Stora, T., Salvetat, J., Maier, F., Stockli, T., Duschl, C., Forr6, L., Heer, W., Chatelain, A. - Purification and size selection of carbon nanotubes , Adv. Mater. 9(10) (1997) 827... 

Figure 3.33 Appearance of the TiOi nanotube-array film at key stages in the fabrication process (a) as-deposited Ti film (b) film after anodisation and (c) transparent film after heat treatment to crystallise the tubes and oxidise the remaining metallic islands. Reprinted from Mor et al., 2006 . Copyright (2006) American Chemical Society...

Hollow carbon nanotubes (CNTs) can be used to generate nearly onedimensional nanostrutures by filling the inner cavity with selected materials. Capillarity forces can be used to introduce liquids into the nanometric systems. Here, we describe experimental studies of capillarity filling in CNTs using metal salts and oxides. The filling process involves, first a CNT-opening steps by oxidation secondly the tubes are immersed into different molten substance. The capillarity-introduced materials are subsequently transformed into metals or oxides by a thermal treatment. In particular, we have observed a size dependence of capillarity forces in CNTs. The described experiments show the present capacities and potentialities of filled CNTs for fabrication of novel nanostructured materials. 

---