Waterborne polyurethane composites with asymmetric multilayered electromagnetic gradient for absorption dominated electromagnetic interference shielding

Absorption dominated electromagnetic interference (EMI) shielding composites have high EMI shielding effectiveness (SE) while eliminating electromagnetic (EM) radiation to the environment, making them vital for solving EM pollution problems. However, there is a lack of composite with both strong EM wave absorption and high EMI SE. Herein, we report an ingenious layer-by-layer (LBL) casting method to prepare waterborne polyurethane/iron oxide/carbon nanotube/reduced graphene oxide (WPU/Fe₃O₄/CNT/rGO, WFCR) EM wave absorber. A positive conductive gradient and a negative magnetic gradient are formed by controlling the composition, and EM wave absorption is enhanced by the asymmetric EM gradient structure. Subsequently, EM wave undergoes the process of “absorption-reflection-reabsorption” induced by the Ag reflection layer prepared by screen printing. Caused by the plentiful EM wave loss mechanism including magnetic loss, interface polarization and conductive loss in Ag-WFCR composites, EMI SE reaches 38.96 dB, and the absorption coefficient (A) value is 0.68, which intuitively demonstrates that the EMI shielding mechanism is dominated by absorption. In addition, the high tensile strength of 9.25 MPa and the compressive strength of 556.2 kPa also indicates its good mechanical properties. These excellent performances demonstrate the promising application of Ag-WFCR composites in EMI shielding and thermal management applications as well as in wearable electronics.