Research On The Formation Mechanism Of Polyaniline Nanotubes Doped With Organic Acids

As a conductive polymer, polyaniline is featured with facile synthesis, acid dopability, high stability, moderate conductivity etc. Furthermore, it also displays excellent optical, electrical and magnetic properties, which makes it valuable in the fabrication of batteries, capacitors, light-emitting diodes, chemical and gas sensors and other devices. Therefore, it has attracted many researchers’ attention. The morphology of nanostructured polyaniline, including its size and properties, can vary drastically depending on the synthetic methods. In order to have a precise control of the structure as well as the morphology of the product, it is required to have an in-depth understanding on the main factors affecting the relevant processes, especially the evolution of the major molecular interactions in this process. In this paper, in-situ solution state1H NMR in combined with synthetic experiments was carried out in an effort to have a preliminary investigation on the formation mechanism of polyaniline nanotubes.The main work of this thesis includes the following areas:(1) Different concentrations of salicylic acid affecting on applied force of main species in the micelle of aniline is studied by a series of NMR techniques such as1H NMR, the measurement of proton spin-lattice relaxation time (T1H) and the diffusion coefficient of aniline as measured by diffusion order spectroscopy (DOSY). We find that aniline monomer will eventually gathered around salicylic acid to form spherical micelles through rapid proton exchange between aniline and anilinium cations. It is found that the micelles system synthetizing polyaniline nanotubes are different from the traditional micelles, where the aggregation between major species is loose and anline monomer therein has a strong mobility. These results are of fundamental importance for the understanding the generation of tublar structure of polyaniline in the reaction.(2) A series of doped polyanilines have been prepared at the varied concentration of acetic acid and oxalic acid, the mount of carboxyl in doping agent and the carbon chain of doping agent. By comparing the structure, the doping state, the crystallinity and the morphology of the prepared polymers, the effect of these experimental parameters on the structure of polymer has been derived. Specifically, the following conclusions can be made:①the morphology of polyaniline is of little affected by the concentration of acetic even though that of the oxalic acid has a strong impact. Generally the product exhibits a relative more unique morphology inclined to display an enhanced crystallinity.②carboxylic acids impact the morphology of polyaniline in two ways:the acidity and structure of a dicarboxylic acid with short aliphatic chains affect the morphology of polyaniline heavily while the acidity becomes the dorminant one for acid with a long carbon chain.③The morphology of polyaniline doped by monocarboxylic acid or dicarboxylic acid is mainly nanofibers and nanotubes. From the result of②and③, we can get carboxylic acid affecting on aniline micelle is a competitive procedure:carboxyl is helpful to stabilize the aniline micelle, but the increase of carbon chain leads to irregular morphologies.