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

In this work, novel core–shell Fe 3 O 4 nanoparticles were prepared by self- assembly technology using phytate-melamine aggregates (PM) or phytate-melamine-Fe 3+ aggregates (PM-Fe) as building block. A polyurea (PUA) matrix was filled with magnetic nanoparticle. The influence of Fe 3 O 4 , Fe 3 O 4 @PM or Fe 3 O 4 @PM-Fe content and dispersion on the mechanical and electromagnetic wave (EMW) absorption properties of PUA composite were investigated. Good dispersion of modified Fe 3 O 4 in PUA matrix was obtained. Loading well-dispersed Fe 3 O 4 significantly enhanced the mechanical properties of their PUA nanocomposite under quasi-static tensile, nanoindentation, and dynamic compression tests. Excellent EMW absorption performance of PUA/Fe 3 O 4 @PM nanocomposite was desired. Although well-dispersed Fe 3 O 4 @PM could effectively enhance the mechanical properties, nonetheless it surprisingly plays a negative role in the EMW absorption performance. The Fe 3 O 4 @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 Fe 3 O 4 in the EMW absorption of PUA composite. Furthermore, the Fe 3 O 4 @PM-Fe, obtained by constructing a conductive network on the surface of Fe 3 O 4 @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 Fe 3 O 4  magnetic nanoparticles.