Electrochemical Preparation Of Polypyrrole Nanowires Induced By Macromolecules

Polypyrrole (PPy) is one of the excellent conducting polymers with good stability and high conductivity. The low solubility and infusibility restrict its processing and applications in some fields. The main methods to improve the processibility are adding substitution groups onto polypyrrole and doping with large dopants. PPy synthesized by the two methods will lose its conductivity to certain extent. To circumvent this problem, the best strategy is to prepare polypyrrole directly in the procedure of processing, rather than after it. PPy nanowires, in this thesis, are just the one-dimensional materials prepared under the instruction of such strategy. It has advantages of both conducting polymers and one-dimensional materials. Therefore, studies on the PPy nanowire have become one of the most attractive fields about nanomaterials. However, high cost, low productivity and difficult operation are the common disadvantages of the reported methods used for preparing PPy nanowires. Many efforts have been made in our laboratory to develop a new method for preparing PPy nanowires and explore the mechanism for the formation of PPy nanowires. The research results are mainly included as following:To control the growth of pyrrole by chemical interaction, a new strategy is proposed in this thesis to synthesize PPy nanowiews in the presence of soluble macromolecules that have functional groups to form hydrogen bond with pyrrole monomer. PPy nanowires with diameters of 70~110 nm are successfully prepared electrochemically in the presence of poly(maleic acid-co-vinyl pyrrolidone) (PVP-MA),polyacrylic acid(PAA),poly(maleic acid-co-styrene),and heparin sodium salt. Compared to other methods used for preparing PPy nanowires, the method we used has many advantages for its very short preparation time (30~300 s), facile operation, low cost, and controllable length and diameters. Doping with perchlorate ion, the PPy nanowires prepared in this way will exhibit excellent conductivity (65~100 S/cm).The nucleation and growth mechanism of PPy nanowires was studied by electrochemical method and scanning electron microscopy. It was found that the nucleation of PPy is a three-dimensional instantaneous process in the presence of PVP-MA, PAA and heparin sodium salt; while the nucleation is a three-dimensional progress process in the presence of PVP-PS. The growth of PPy nanowires is a two- or three-dimensional process with the difference of applied potential and has no relationship with the soluble macromolecule. The relationship between the orientation of PPy and the soluble macromolecule was explored. The controlling mechanism for the formation of PPy nanowires was presented and the reliability of the mechanism was proved by the different conductivity among the nanowires with different diameters.The influences of related parameters on PPy morphology were systemically investigated. The experimental results indicate that PPy morphology could be influenced by applied potential, pyrrole concentration, lithium perchlorate concentration, soluble macromolecule concentration, and polymerization time. However, the electrochemical preparation methods and the electrodes (graphite electrode, ITO electrode and stainless steel electrode) have no effects on PPy morphology.