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In this work, the engineered polyaniline (PANI)/epoxy composites reinforced with PANI-M (physical mixture of PANI spheres and fibers) exhibit significantly enhanced electromagnetic wave absorption performance and mechanical property. Due to the synergistic effect of PANI fillers with different geometries, the reflection loss of 10.0 wt% PANI-M/epoxy could reach − 36.8 dB at 17.7 GHz. Meanwhile, the mechanical properties (including tensile strength, toughness, and flexural strength) of PANI/epoxy were systematically studied. Compared with pure epoxy, the tensile strength of epoxy with 2.0 wt% PANI-M was improved to 86.2 MPa. Moreover, the PANI spheres (PANI-S) and PANI fibers (PANI-F) were prepared by the chemical oxidation polymerization method and interface polymerization method, respectively. The characterizations including scanning electron microscope, Fourier transform infrared spectra, and X-ray diffraction were applied to analyze the morphology and chemical and crystal structures of PANI filler. This work could provide the guideline for the preparation of advanced engineered epoxy nanocomposites for electromagnetic wave pollution treatment. Graphical abstract

Tunable positive magnetoresistance (MR) of polyaniline (PANI) nanocomposites with different magnetic nanoparticles (Fe3O4 or CoFe2O4) have been prepared through the facile surface-initiated polymerization (SIP) method. The characterizations including Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM) indicate that the magnetic nanoparticles were successfully coated by PANI. A quasi 3D variable range hopping (VRH) mechanism was observed in the magnetic PANI nanocomposites through Mott VRH model. The effects of magnetic field and magnetic nanoparticle on the charge carrier’s behavior were studied by the wave function shrinkage model. The localization length and average hopping length decrease with increasing magnetic field, while the density of state at the Fermi level increases with increasing magnetic field. The enhanced dielectric property and magnetic property of the magnetic PANI nanocomposites were reported as well. Magnetic polyaniline nanocomposites with tunable positive magnetoresistance.