Multilayer WPU conductive composites with controllable electro-magnetic gradient for absorption-dominated electromagnetic interference shielding

A well-designed multilayered waterborne polyurethane (WPU) shielding composites with absorption-dominated shielding feature are realized by constructing a controllable electro-magnetic gradient. Using the layer-by-layer casting method with reasonable arrangement of Fe3O4@rGO and MWCNT nanofiller, an ordered multilayer shielding network can be constructed to provide the WPU composites with positive electrical conductivity gradient and negative magnetic gradient. Hence, the penetrating microwave would undergo a particular "absorption-reflection-reabsorption" process and interface polarization loss induced absorption process between impedance matching layer and high conductive layer, leading to rather low microwave reflection with effect electromagnetic interference shielding effeteness (EMI SE). With the increase of electro-magnetic gradient, the EMI SE of the Fe3O4@rGO/MWCNT/WPU composites reaches 35.9 dB, while the power coefficient of reflectivity can be significantly decreased to 0.27. This work offers a feasible strategy for designing absorption-dominated shielding material with tunable electromagnetic performance that suitable for next-generated smart electronic devices.