Preparation and magnetic and thermal properties of flexible polyimide films with iron nitrophthalocyanine-coated magnetite microspheres

To effectively utilize the one-step solvent–thermal route to prepare iron (Fe)–nitrophthalocyanine/magnetite (Fe₃O₄) hybrid microspheres, we have developed a novel series of flexible Fe₃O₄/Fe-phthalocyanine (FePc)/polyimide (PI) composite films with various Fe₃O₄/FePc nanoparticle loadings (15, 27, and 40 wt%) and imidized at different temperatures (200°C and 300°C). The morphology and structure of the composite films were monitored using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction, and the hybrid microspheres were found uniformly dispersed in the polymer matrices without any agglomeration. Mechanical and thermal properties of the composites were also investigated. The observed results indicated enhanced thermal stabilities, dramatically increased tensile modulus, and increased glass transition temperatures of the composite films, with the increment in the content of inorganic nanoparticles. Besides that, the Fe₃O₄/FePc/PI magnetic films showed higher saturation magnetization (24.33 emu g⁻¹, 27 wt% Fe₃O₄/FePc loading) with high-temperature treatment compared with that of the Fe₃O₄/PI film (18.79 emu g⁻¹, 27 wt% Fe₃O₄ loading). It proved to be an effective way to prevent Fe₃O₄ nanoparticles from oxidizing by coating the nanoparticles with organic layer. The flexible composite films can easily be moved under a relatively low magnetic field, indicating them to be the high-performance absorbing materials in potential applications.