Electromagnetic Field Shielding Polyurethane Nanocomposites Reinforced with Core-Shell Fe-Silica Nanoparticles

A modified Stober method is introduced to synthesize Fe@SiO2 nanoparticles (NPs) using 3-aminopropyltriethoxysilane (APTES) as a primer to render the metal particle surface compatible with silica. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) results indicate a highly crystalline iron core coated with a uniform layer of silica. Polyurethane (PU) nanocomposites filled with 71 wt % Fe@FeO and 71 wt 96 Fe@SiO2 NPs are fabricated via a surface-initiated polymerization (SIP) method. The significantly increased coercivity of the resulting nanocomposites than that of the pure Fe@FeO NPs indicates that the NPs become magnetically harder after being dispersed in the PU matrix. Both Fe@SiO2 NPs and Fe@SiO2/PU nanocomposites exhibit better thermal stability and antioxidation capability than Fe@FeO and Fe@FeO/PU, respectively, owing to the barrier effect of the silica shell, revealed by the thermalgravimetric analysis (TGA). Meanwhile, the silica shell greatly reduces the eddy current loss and increases the anisotropy energy, which is essentially important to acquire higher reflection loss and broader absorption bandwidth for the microwave absorption. The Fe@SiO2/PU nanocomposites show good electromagnetic wave absorption performance (reflection loss, RL < -20 dB) at high frequencies (11.3 GHz), while the best RL of Fe@FeO/PU is still larger than -20 dB even with a larger absorber thickness.