Poorly-/well-dispersed Fe₃O₄: Abnormal influence on electromagnetic wave absorption behavior of high-mechanical performance polyurea

In this work, novel core–shell Fe₃O₄ nanoparticles were prepared by self- assembly technology using phytate-melamine aggregates (PM) or phytate-melamine-Fe³⁺ aggregates (PM-Fe) as building block. A polyurea (PUA) matrix was filled with magnetic nanoparticle. The influence of Fe₃O₄, Fe₃O₄@PM or Fe₃O₄@PM-Fe content and dispersion on the mechanical and electromagnetic wave (EMW) absorption properties of PUA composite were investigated. Good dispersion of modified Fe₃O₄ in PUA matrix was obtained. Loading well-dispersed Fe₃O₄ significantly enhanced the mechanical properties of their PUA nanocomposite under quasi-static tensile, nanoindentation, and dynamic compression tests. Excellent EMW absorption performance of PUA/Fe₃O₄@PM nanocomposite was desired. Although well-dispersed Fe₃O₄@PM could effectively enhance the mechanical properties, nonetheless it surprisingly plays a negative role in the EMW absorption performance. The Fe₃O₄@PM with high dispersion and interfacial compatibility in the PUA matrix was detrimental to EMW absorption performance, which contradicts the well accepted EMW absorption mechanisms. A novel mechanism and model were suggested, along with a fresh understanding of the role of Fe₃O₄ in the EMW absorption of PUA composite. Furthermore, the Fe₃O₄@PM-Fe, obtained by constructing a conductive network on the surface of Fe₃O₄@PM, was used to investigate this assumption. The radar cross section simulation also demonstrated the superior EMW attenuation capability of PUA nanocomposites in the service condition. This work is beneficial to the development of EMW absorber, not limited to Fe₃O₄ magnetic nanoparticles.