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) and PM-Fe as building block. A polyurea (PUA) matrix 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 was 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.