Waterborne polyurethane aerogel with asymmetric gradient structure formed by density-induced self-stratification for absorption-dominated electromagnetic interference shielding

The issues of electromagnetic (EM) emission and its secondary contamination have prompted significant concern among individuals. Hence, the development of efficient absorbing electromagnetic interference (EMI) shielding materials are urgent. Herein, silver-coated and foamed temperature-sensitive microspheres (Ag@FTSM) were synthesized by electroless silver plating. Subsequently, the Ag@FTSM/Fe₃O₄/waterborn polyurethane (WPU) composite aerogels with a porous and asymmetric gradient structure were prepared via freeze-drying process based on the principle of density difference. The introduction of the porous structure can reduce the material density and filler addition, augment the loss interface, and prolong the conduction path resulting in the enhancement of the EM wave absorption property. Through the loss mechanism of “absorption-reflection-reabsorption” and the longer loss path of the aerogels, the EMI shielding efficiency (SE) of the composites reached 48.7 dB with excellent absorption efficiency (46.5 dB) and high absorption coefficient (0.60) when the electromagnetic waves hit the magnetic layer.