| Conductive polyaniline (PANI) as a new material of functional polymer is given more and more attention by scientists because of its simple synthesis methods, particular doping mechanism, excellent environmental stability, as well as wide application. However, the properties of infusibility and insolubility are the obstacles of its application.The magnetic field effect has a marked impact on free radical polymerization. Whereas, magnetohydrodynamic effect can result in the increasing mass transfer efficiency, affecting polymerization's rate and process. Simultaneously, because PANI has anisotropic diamagnetic susceptibility, which causes its internal structure unit preferring to grow and arrange along with a particular direction in the presence of external magnetic field, that is, to take certain degree of orientation, which makes product molecular chains aligned more orderly with more regular structure; in the meantime, the material shows anisotropy in physical property. Through its impact on PANI's micro-structure, such as the conjugate chain length, the regularity of the molecular chain as well as aggregation state, etc., the magnetic field affects PANI's macroeconomic property, such as: increase of PANI's conductivity, dissolution /dispersion, pyrolysis temperature to varying degrees.Two kinds of Polyaniline doped with dodecyl benzene sulfonic acid were synthesized by emulsion polymerization under the presence and absense of a constant magnetic field (0.4T) respectively. The effects of magnetic field on the polymerization of aniline and the product's orientation structure and properties were contrastive investigated using transmission electron microscopy, atom force microscopy, gel permeation chromatography, FT-IR spectroscopy, X-ray diffraction, four-point probe conductivity, laser particle size analysis, current voltage, Tafel curve, the resistance anisotropy of the PANI/PVA composite film, and the conductivity change of the PANI/m-cresol solution under an external electric field, and the PANI's orientation structure was successfully characterized through innovative methods.The results showed that compared with polymerization of aniline under the absence of magnetic field, the rate and yield of polymerization of aniline under the presence of magnetic field increased, the resulted product's molecular weight, conductivity, dissolution dispersity, anticorrosion, thermal stability and crystallization were better. It was also observed that no effect of magnetic field on the basic structural units of polyaniline, but there was significant microcosmic preferred orientation in the PANI synthesized under the presence of magnetic field in comparation with PANI synthesized under the absence of magnetic field because of its greatly enhanced anisotropic diamagnetic susceptibility, which leaded to obvious differentiation in the response characteristics to magnetic field in different directions and thus had greatly enhanced the orientation when particles aggregated. Its particles arrange and pack orderly and form plenty of strip aggregation with some ratio of the length to width, and the microcosmic preferred orientation arrangement would evolve into macroscopic orientation when it was magnetized, thereupon the anisotropic electrical conductivity in this PANI was identified.When the emulsifier/monomer molar ratio, initiator/monomer molar ratio, reaction temperature, reaction time and the pH range were 0.5, 0.8, room temperature, 4h and 2.5~3, magnetic field had important effects on the polymerization of aniline and the product's structure and properties, the orientation level of the PANI synthesized under the presence of magnetic field (0.4T) was higher and its main indexes of structure and performance were more prominent, and generally better than that of the PANI synthesized under the absence of magnetic field.
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