Synthesis Of Polyaniline Micro/Nanostructures In Aqueous Alkaline Solution

Polyaniline (PANI) is an important member in the family of"synthetic metals"that has been widely studied for a variety of applications ranging from lightweight batteries, electromagnetic shielding devices, anticorrosion coatings, optical or electronic devices, gas-separation membranes, and chemical or biological sensors etc. for its low cost, easy synthesis, good processibility, excellent environmental stability and reversible acid/base doping/dedoping chemistry. Recently, micro/nanostructured polyaniline has attracted special attention in both chemical and material fields because of the rapid emergence and development of nanoscience and nanotechnology. The researchers are re-examining various aspects of chemistry and physics of polyaniline under the"nano"scopes, thus make it becoming an important low-dimensional material.Up to now, there have been many reports on polyaniline micro/nanostructures, which were produced with various strategies such as templates, surfactants, interface and self-assembly method and so on. All those micro/nanostructures were well prepared and each method had its strongpoint. Nevertheless, one great challenge is to fabricate functional, controlable structures with micro/nanoscale features in a facile way, at a low cost, and with a high throughput. As one of conducting polymers, polyaniline can change from an initial insulating state to an electrically conducting state after protonic doping treatment. Therefore, polyaniline was usually synthesized at lower pH condition. However, it has been proved in our research works that the type of polyaniline micro/nanostructures related to pH sensitively on the synthetic method employed, which has not got enough attention previously. As we know, low-dimensional structures play an important role in determining material properties and promising potential application. Therefore, we should not only think of the improvement of the electrically conducting properties, but also pay attention to the properties of structural materal. Recently, some reports have noted this phenomenon, and tabled a proposal to synthesize polyaniline micro/nanostructures with wider range of pH.In this thesis, we succeeded in synthesizing multi morphologies of polyaniline micro/nanostructures by oxidative polymerization of aniline (An) in aqueous alkaline solution without any external physical or chemical templates, dopants and additives. We discussed the changing of morphologies, molecular structures and the polymerization mechanism in this alkaline condition. In aqueous alkaline solution, we not only realized the semiconducting intrinstic properties of the produces, but also present a new approach to obtain many kinds of low-dimensional structural materals, and gave an opportunity to apply this method in the fields of functional biomaterials and structural materials. The main results are summarized as follows:(1) It is an effective and easy way to synthesize polyaniline micro/nanostructures in aqueous alkaline solution without external physical or chemical templates, dopants and additives. Only by changing the pH or the concentration of aniline, the controllable polyaniline structures from 1D nanotubes to 3D hollow microspheres could be obtained by the"Alkali-guided"method. As a whole, spheres became dominating when the molar ratio of aniline monomer to sodium hydroxide (shortening as An/NaOH) was less than 1: 1, well, seamless hollow microspheres were got in higher pH value combined with lower [An]; when the molar ratio of An/NaOH was more than 1: 1, nanotubes were dominating, but, ringent hollow microspheres were formed in lower pH value combined with higher [An]. In addition, both 1D and 3D structures reduced their size with the increasing of pH value.(2) The studies of mechanism of polymerization indicated that aniline monomer could frame various primary structures co-acted by NaOH and ammonium persulfate (APS) at the early alkaline stage. Then the pH fell with the process of polymerization for the reduction product of sulfuric acid. Therefore, the conventional polyaniline chain grew after the initial induction period, and then assembled into micro/nanostructures by (self-) doped with sulfate radical in some sense. Therefore, the produces are semiconductor with a conductivity of 10–2 S/cm. The heterostructures lead to the relative lower conductivity.(3) The structure of supermolecular of compounds of tryptophan heteropoly tungstutes by the single crystal X-ray analysis. Multitudinal interactions were identified within the chiral space group P43212. The knowledge about the interaction sites and the structure provides a unique opportunity to understand its molecular or chiral recognition properties.