Eco-friendly waterborne polyurethane-based coatings with spontaneously formed gradient distribution architectures achieved absorption-enhanced electromagnetic interference shielding and infrared stealth

Electromagnetic interference (EMI) shielding and infrared (IR) stealth technologies play crucial role in modern industrial and military fields. However, the secondary pollution of electromagnetic waves (EMWs) generated by reflection-dominated EMI shielding materials is undesirable. Therefore, preparing eco-friendly coatings that integrate electromagnetic protection and thermal camouflage while reducing the EMWs reflectivity through simple methods is of great significance. This paper proposes a straightforward strategy: using tannic acid (TA)-modified MXene as the conductive fillers and waterborne polyurethane (WPU) as the matrix, gradient structure is spontaneously formed within the coatings via a one-step spraying method. The resulting composite coatings achieve excellent EMI shielding effectiveness (37.4 dB) and high absorption coefficient (0.41). Under the synergistic protection of WPU and TA, composite coatings maintain superb EMI shielding performance (retention rate exceeding 93 %) in harsh environments. Due to the low IR emissivity of MXene, composite coatings also exhibit satisfactory IR stealth performance under different temperature fields, which not only achieve ideal camouflage of human body and significant reduction of detection signal in the medium (60 ℃) and high (120 ℃) temperature environments. Finally, benefiting from the adhesive properties of WPU, composite coatings perform outstandingly in both qualitative and quantitative adhesion tests. This study provides important references for the design and fabrication of multifunctional protective coatings in commercial and military applications.