Polyaniline (PAn) doped with dodecyl benzenesulfonic acid was synthesized by emulsion polymerization in the presence of a constant magnetic field (0.4 T). The micro-morphology and orientation microstructure of the PAn were systematically investigated using transmission electron microscopy, X-ray diffraction, FT-IR spectroscopy, conductivity, the resistance anisotropy of the PAn/PVA composite film and the conductivity change of the PAn/m-cresol solution under an external electric field, showing that compared with the PAn_-O synthesized in the absence of a magnetic field, there is significant microcosmically preferred orientation in the PAn_-M synthesized in the presence of a magnetic field, their particles arrange and pack orderly to form plenty of strip aggregates with some ratio of the length to width, and they achieve conforming orientation when magnetized. In addition, the PAn-_M is obviously found to have higher crystallinity. The PAn_-M/PVA composite film cured under a condition of magnetization shows the remarkable anisotropic electrical conductivity. And the m-cresol solution prepared from PAn_-M underwent an obvious abrupt change in its conductivity from the presence of an external electric field to its absence. It was thought that because of the existence of microcosmically preferred orientation, the macroscopic orientation of the PAn_-M was evolved in the presence of an outside magnetic field, and the anisotropic electrical conductivity in this PAn was identified here.

Key words: polyaniline, magnetic field, orientation microstructure, anisotropic electrical conductivity