Preparation And Characterization Of Polyaniline And Its Derivatives, Micro / Nano Materials

As the most investigated conducting polymers, polyaniline (PANI) and its derivatives have attracted considerable attention due to their special doping mechanism, high environmental stability, ease of processability and low cost, and potential applications in batteries, chemical sensors, light-emitting diodes, gas separation membranes and molecular electronic devices etc. With the development of nanoscience and nanotechnology and the obvious morphology dependent material properties and applications, controlled synthesis of micro/nanostructured PANI has aroused increasing attention. Up to date, "hard template", "soft template" and "templateless" are the three main strategies towards morphology control of PANI. Most of the studies are focusing on the synthesis of PANI one-dimensional nanofibers and nanotubes, two-dimensional networks and three-dimensional spherical structures, however, the preparation of PANI with hierarchical structures based on self-assembled one-dimensional structures and with special unusual structures are still lacking. Designed synthesis of those kinds of PANI materials is still a challenge to material scientists. Besides, despite the variety of synthetic methods reported for PANI micro/nanostructures, micro/nanostructured PANI derivatives have been synthesized with only limited success. Therefore, in this article, we propose some new methods based on the three synthetic methods as mentioned above for the preparation of PANI hierarchical structures and PANI derivatives with special morphology. The formation mechanism and the applicability of the methods are discussed. The main results are as follows:(1) Leaf-like PANI based on self-assembled one-dimensional nanostructures are synthesized with the aid of micelles formed by an amphiphilic triblock copolymer surfactant. Such one-dimensional nano structures are arranged with parallel alignment along the long axis and short axis and then result in the mat-like arrays. By changing the synthetic parameters, the building blocks of leaf-like PANI can be altered from nanofibers to nanorods and even to nanotubes, and the sizes of leaf-like PANI can also be tuned. Mechanism investigations demonstrate that the absence of a doping acid and the presence of a surfactant with hydrophilic EO chains are essential for the construction of nanostructure-based leaf-like morphology of PANI.(2) Rectangular tubes of PANI/NiO composites ranging in size from nanometer to micrometer are synthesized through a self-assembly process in the presence of micelles formed by anionic surfactant sodium dodecylbanzenesulfonate (SDBS). The coordination bond formed between the atom of nitrogen in PANI and that of nickel in NiO nanoparticles is the key factor in the formation of the right angle of PANI/NiO rectangular tubes. By changing the experimental parameters, high flexible PANI/NiO composite nanobelts with rectangular cross section can also be obtained.(3) A novel morphology of PANI derivatives hollow microsphere with one single opening in the surface can be obtained by the droplet template formed by the monomer itself through a one-step solution route. The diffusion flux of monomers during the polymerization processes may lead to the formation of the hole in the shell of each hollow microsphere. The size of hollow microspheres and the size of the hole in the surface of each hollow sphere can be controlled by changing the experimental parameters. This simple and environmentally friendly strategy can be used to the preparation of many PANI derivativess hollow microspheres with holes in their surfaces, such as poly(o-toluidine), poly(m-toluidine), poly(p-toluidine), poly(o-methoxyaniline) and poly(o-phenylenediamine) hollow microspheres. Therefore, this a general synthetic strategy towards this kind hollow microspheres of PANI derivatives.(4) A general route, involves swelling-evaporation processes, has been developed for the generation of hollow nanospheres of PANI derivatives, with the use of swelling properties of PANI derivatives. Different swelling reagents can affect the morphology of resultant polymer hollow structures, while the evaporation conditions, such as temperature and pressure, can be utilized to tune the size and shell thickness of polymer hollow structures. This will provide insights in the synthesis of hollow nanospheres of PANI derivatives.(5) Poly(o-toluidine) (POT) nanofibers can be fabricated by using HAuCl₄ instead of the traditional used ammonium persulfate as the oxidant through one-step chemical route. By changing the concentration of HAuCl₄, the diameter of POT nanofibers can be tuned from 200 to 10 nm. The gold nanoparticles generated during the polymerization processes are considered to act as catalysts to the oriented growth of POT nanofibers. This novel templateless method can also be applied to the synthesis of nanofibers of other PANI derivatives.(6) Gold nanoparticles supported on both inner and outer shells of hollow microspheres of poly(o-phenylenediamine) (PoPD) can be successfully obtained using PoPD hollow microspheres both acting as the template and reductant, which will achieve the surface functionalization of PoPD hollow spheres. The sizes of gold nanoparticles can be tuned by changing the experimental parameters. Furthermore, gold nanorods can be fabricated by introducing a seed growth strategy. Other reactive templates can also be used for the preparation of glod nanoparticles supported on polymer, such as poly(o-toluidine) and poly(o-methoxyaniline) hollow microspheres, and PANI nanotubes. Moreover, besides the formation of gold nanoparticles supported on polymer hollow microspheres, other metal nanoparticles, such as silver nanoparticles supported on polymer hollow microspheres can also be synthesized using the same synthetic strategy when altering gold salt with silver salt. The synthesized polymer supported gold nanoparticles have potential application in organic catalytic reaction.