Efficient Electromagnetic Interference Shielding of PPA6@NiM/PDMS Composites with Porous and Asymmetric Gradient Structures

In this work, magnetic PA6 microspheres (PPA6@NiM) with porous structures were prepared using the solvent co-precipitation method and electroless nickel plating technology, and the stacked magnetic microspheres were encapsulated with polydimethylsiloxane (PDMS) to obtain PPA6@NiM/PDMS composites. The existence of the porous structure increases the attenuation path of the electromagnetic wave, and the presence of the nickel layer improves the magnetic loss of the composite material to the electromagnetic wave and synergistically improves the absorption of the electromagnetic wave. Among them, the total shielding effectiveness (SET) of the PPA6@NiM4/PDMS composite is as high as 39.9 dB, and the reflection coefficient (R) is 0.83. To further increase the absorption effect of the composite material, an asymmetric gradient structure was constructed by utilizing the difference in electrical conductivity between the magnetic microspheres. The electromagnetic wave is incident from the surface with lower conductivity (impedance matching layer). It is reflected by the consistency with higher conductivity (strong reflective layer) than the bottom layer to increase the loss of electromagnetic waves inside the material. The composite SET constructed with M1 and M4 particles with the most significant difference in conductivity achieved 35.5 dB with an absorption coefficient (A) of 0.42. It shows that the porous combined asymmetric gradient structure we designed can effectively improve the shielding efficiency and absorption capacity of the composite material against electromagnetic microwaves and serve as a reference for creating high-absorbing and high-performance electromagnetic shielding materials.