Magnetoresistive Conductive Polyaniline–Barium Titanate Nanocomposites with Negative Permittivity

Abstract

Polyaniline (PANI) polymer nanocomposites (PNCs) filled with barium titanate (BaTiO 3) were synthesized by a surface initiated polymerization method. Two different particle sizes (100 and 500 nm) were studied. By varying the loading level, size of BaTiO 3 nanoparticles (NPs) and stirring method for the polymerization process, a series of PNCs were obtained and the effects of these parameters on the crystalline structure, thermal stability, morphology, electrical conductivity and dielectric permittivity were systematically studied. FT-IR analysis indicated a strong interaction between the formed PANI and the BaTiO 3 NPs, and TEM observations showed that the BaTiO 3 NPs are well coated with a PANI layer, however, the thickness of the PANI layer decreased with increasing the BaTiO 3 particles loading. The XRD reflection patterns indicated that the crystallinity of the polyaniline part in the PNCs depends on the nanoparticle loading. However, the resistivity does not increase with increasing the crystallinity, and the temperature dependent resistivity result reveals a 3-d variable range hopping (VRH) electron transport mechanism. The BaTiO 3 loading dependent resistivity is interpreted from the dominating space charge on the BaTiO 3/PANI interface and the ferroelectric nature of BaTiO 3 for the PNCs with different particle loadings. Compared with the positive real permittivity for the PNCs prepared from physical mixing, all the chemically synthesized PNC samples show negative dielectric permittivity and the permittivity change is related to the instinct metallic state in PANI. In addition, positive magnetoresistance (MR) is observed in all kinds of PNCs and analyzed theoretically from the wave function shrinkage model. © 2012 American Chemical Society.