Magnetoresistive Polyaniline/Multi-Walled Carbon Nanotubes Nanocomposites With Negative Permittivity

Polymer nanocomposites (PNCs) consisting of multi-walled carbon nanotubes (MWNTs) and polyaniline (PANI) were synthesized by a surface initiated polymerization (SIP) method with hexavalent chromium (Cr(VI)) as oxidant. The PNCs with ammonium persulfate (APS) as oxidant were also prepared for comparison. The Fourier transform infrared (FT-IR) spectroscopic analysis indicated a strong interaction between MWNTs and hosting PANI matrix. An enhanced thermal stability was observed in the PNCs compared with that of pure PANI. Temperature dependent resistivity analysis revealed a quasi 3-dimensional variable range hopping (VRH) electrical conduction mechanism for the as-received MWNTs and all the synthesized nanocomposite samples. These PNCs show the frequency dependent permittivity. Negative giant magnetoresistance (GMR) (around -2%) was observed in the PNCs oxidized by Cr(VI) and positive GMR was observed in the as-received MWNTs, pure PANI and PNCs oxidized by APS. The observed positive and negative GMR effects were well explained by wave function shrinkage model and orbital magnetoconductance theory by calculating the changed localization length (a₀), density of states at the Fermi level (N(E_F)), and reduced average hopping length (R_hop).