Synthesis of electromagnetic functionalized nickel/polypyrrole core/shell composites.

Microstructured Ni/PPy (PPy: polypyrrole) core/shell composites were prepared from an in situ chemical oxidative polymerization of pyrrole (Py) monomer in the presence of Ni powder, with ammonium persulfate (APS) as oxidant and citric acid (C6H8O7) as dopant. X-ray diffraction and Fourier transform infrared analyses indicate that there is no chemical interaction between Ni powder and protonated PPy. The mass percentages of PPy, calculated from the remanent weight percentages of Ni/PPy composites after thermogravimetric analysis, are in consistent with those as designed. The prepared Ni/PPy composites are soft and ferromagnetic materials, where a linear increase of saturation magnetization (MS) and remanent magnetization (MR) as a function of Ni powder content is proposed. The permeability of Ni/PPy composites presents a natural magnetic resonance at 6.0 GHz, and Cole-Cole semicircle was applied to explain the permittivity. Electromagnetic absorption less than -10 dB is found for Ni/Py=4:1 (11-15.4 GHz) and Ni/Py=2:1 (12-17.5 GHz). The ternary Debye relaxations for enhanced dielectric loss induced by PPy coatings and proper electromagnetic impedance matching due to the synergetic consequence of the Ni cores and PPy shells contribute to the improvement of the electromagnetic absorption of the Ni/PPy core/shell composites. It is important to notice that dielectric loss and electrical conductivity should be considered simultaneously in designing dielectric-type electromagnetic absorbing materials.