(143g) Magnetoresistive Conductive Polyaniline - Barium Titanate Nanocomposites with Negative Permittivity

Conductive polyaniline (PANI)-based polymer nanocomposites (PNCs) with barium titanate (BaTiO₃) were synthesized by a surface initiated polymerization (SIP) method. Two different particle sizes (100 and 500 nm) were studied. By varying the loading level, size of BaTiO₃ nanoparticles (NPs) and stirring method, 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 BaTiO₃ NPs, and TEM observations showed that the BaTiO₃ NPs are well coated with a this PANI layer, however, the thickness of the PANI layer decreased with increasing the BaTiO₃ particles loading. The XRD reflection patterns indicated that the crystallinity of PANI 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 resistivity variation with BaTiO₃ loading is mainly attributed to the ferroelectric nature of BaTiO₃ and the space charge on the interface between BaTiO₃ and PANI. Compared with the positive real permittivity for the PNCs prepared from physical mixing, all the chemical 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.