Polyaniline metallic nanoparticle 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. 

A different approach was taken by Kumar and associates [61]. Fie also embedded metals in polymers, but used as his precursor the polymer and not the monomer. In his first study a composite material containing amorphous Cu nanoparticles and nanocrystalline CU2O embedded in polyanUine matrices was prepared by a sonochemical method. These composite materials were obtained from the soni-cation of copper (II) acetate when aniline or 1% v/v aniline-water was used as the solvent. Mechanisms for the formation of these products are proposed and discussed. The physical and thermal properties of the as-prepared composite materials are presented. A band gap of 2.61 eV is estimated from optical measurements for the as-prepared CU2O in polyaniline. 

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]. 

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