Metal-nanofiber composites

The polymer resulting from oxidation of 3,5-dimethyl aniline with palladium was also studied by transmission electron microscopy (Mallick et al. 2005). As it turned out, the polymer was formed in nanofibers. During oxidative polymerization, palladium ions were reduced and formed palladium metal. The generated metal was uniformly dispersed between the polymer nanofibers as nanoparticles of 2 mm size. So, Mallick et al. (2005) achieved a polymer- metal intimate composite material. This work should be juxtaposed to an observation by Newman and Blanchard (2006) that reaction between 4-aminophenol and hydrogen tetrachloroaurate leads to polyaniline (bearing hydroxyl groups) and metallic gold as nanoparticles. Such metal nanoparticles can well be of importance in the field of sensors, catalysis, and electronics with improved performance. 

S. Virji, J. D. Fowler, C. O. Baker, J. Huang, R. B. Kaner, and B. H. WeiUer, Polyaniline nanofiber composites with metal salts Chemical sensors for hydrogen sulfide. Small, 1,624-627 (2005). 

K. MaUick, M.J. Witcomb, A. Dinsmore, and M.S. Scurrell, Fabrication of a metal nanoparticles and polymer nanofibers composite material by in situ chemical synthetic route, Langmuir, 21, 7964-7967 (2005). 

A gas-solid reaction was further introduced to the electrospiiming technique to incorporate semiconductor nanostructures into polymer nanofibers with better dispersion. The production of well-dispersed PbS nanoparticles in polymer fiber matrices has been achieved by this method (Lu et al., 2005). First, metal salt and polymer were codissolved into one solvent to make a homogeneous solution. Then the above solution was electrospun to obtain polymer/metal salt composite nanofibers. The composite nanofibers were finally exposed to HaS gas at room temperature to synthesize PbS nanoparticles in situ in polymer nanofibers. 

Acids can act as dopants for polyaniline therefore, if the nanofibers are first doped with these acids, and subsequently exposed to the metal ions, precipitates should be formed on the surface of the nanofibers, leading to inorganic-polyaniline nanofiber composites. This idea has been applied in Section 7.3.5 to improve the detection of H2S. Another possibility is to use nanofibers as nucleation seeds to collect inorganic nanoparticles from supersaturated solutions [148]. 

ElectrochemicaUy active materials such as activated carbons, carbon aerogels, and carbon foams (aU derived from polymers) oxides, hydrous oxides, carbides, and nitrides are used to form composites with carbon nanofibers. Additional active materials such as oxides, hydrous oxides, and carbides can be combined to form a composite. Process requires dispersion in water with carbon nanofiber and subsequent filtralion and washing. Capacitance of 249 F /g was measured from a RuOj xHjO metal oxide and carbon nanofiber composite. 

Historically, electrospinning was used to produce nanofibers from polymer materials. However, electrospun nanofibers of caibon, ceramic, metal and composite materials also have been recently developed. 

The following two sections discuss the effects of different solution properties and operational conditions on the stracture (especially, the diameter) of electros-pun polymer nanofibers. Many carbon, ceramic, metal and composite nanofibers are prepared from solutions that contain polymers, and hence the fundamental knowledge covered in the following sections also gives insight to the stractwe control of these nanofibers. 

In recent years, we have seen an explosive interest in nanomaterials, in particular in nanofibers, nanofilaments, and nanotubes of the very different chemical composition. The interest arises from the specific mechanical and physicochemical properties of these nano objects, which allow them to be used, for example, as specific adsorbents, catalyst supports, reinforcing components of composite materials, and so on. The most cited generic types of nanomaterials are carbon nanofilaments and nanotubes. Numerous methods for preparing these carbon materials are known. However, the simplest method seems to be thermal pyrolysis of various carbon contain ing precursors (e.g., carbon monoxide, saturated and unsaturated hydro carbons, etc.) in the presence of special catalysts that are typically nanosized particles of nickel, cobalt, iron metals, or their alloys with different metals. 

It is reasonable that, in the synthesis of polymer nanocomposites, the y-ray irradiation method is convenient for growing nanofibers and nanowires of metal chalcogenides due to the shape-control of the macromolecules formed in situ. Figure 7.38 shows some of the resulting nanofiber-dispersed polymer composites,... 

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