Multifunctional Polymer Nanocomposites with Core-Shell Structure for Magnetoresistance and Electromagnetic Shielding

The conductive polymer nanocomposites with different nanofillers were synthesized by a surface initiated polymerization (SIP) method. The electron transport mechanism of the conductive polymer nanocomposites was studied by the mott variable range hopping (VRH) model. All the synthesized samples showed 3-dimensional (3-D) VRH mechanism.The nanofillers could affect the magnetoresistance (MR) behavior of polyaniline nanocomposites. Positive MR values of polyaniline nanocomposites with different carbon materials (graphene, carbon fiber, carbon tube and carbon black) were observed, the 2-D graphene/polyaniline nanocomposites showed higher MR than those of polyaniline nanocomposites with 1-D or 0-D carbon nanofillers. The MR of polyaniline nanocomposites with different magnetic nanoparticles was positive as well, and the CoFe2O4(cobalt ferrite)/polyaniline nanocomposites showed higher MR than those of Fe@C/polyaniline and Fe₃O₄(magnetite)/polyaniline nanocomposites at the same loading. However, negative MR was observed in the TiO₂(titania)/polyaniline nanocomposites. The negative MR increased with increasing the TiO₂ loading in the polyaniline nanocomposites. The wave-function shrinkage model and forward interference model were applied to study the positive MR and negative MR of the polyaniline nanocomposites, respectively. The localization length, density of state at fermi level and average hopping length were affected by the nanofillers, loadings and magnetic field.The enhanced electromagnetic shielding performance and thermal stability were observed in the Fe3O4/polypyrrole nanocomposites. The highest shielding effectiveness (SE) was -35.7 dB. The enhanced electromagnetic shielding performance was due to the dielectric loss, magnetic loss (eddy current loss) and improved impedance matching. Meanwhile, the improved thermal stability was induced by the covalent bonding formed between polypyrrole and epoxy matrix, enhanced char residue and nitrogen-containing material.