Low-reflection electromagnetic interference shielding composite foams with asymmetric structure towards infrared camouflage and response switching.

Electromagnetic interference (EMI) shielding materials with low reflection and high EMI shielding effectiveness (SE) have emerged as an important development trend. In this work, heterostructured Ti3C2Tx@CoNi were prepared by in-situ growth method. Then Ti3C2Tx@CoNi/Ti3C2Tx/cellulose nanofiber (CNF) composite foams (TCTCF) with asymmetric structure were prepared by layered freezing and freeze-drying technique. The Ti3C2Tx@CoNi/CNF layer could effectively absorb electromagnetic waves, and the Ti3C2Tx/CNF layer was set up to induce electromagnetic waves to go through the "absorption-reflection-reabsorption" process, so as to achieve excellent EMI SE and low reflection coefficient (R). With the electromagnetic synergy of CoNi and Ti3C2Tx and unique asymmetric structure, TCTCF showed EMI SE of up to 85 dB and reflection loss (SER) of 4 dB, and R was controlled between 0.22 and 0.47. The thermal conductivity (λ) of TCTCF could be adjusted between 26.91 and 84.31 mW/(m·K), meeting the requirements of heat insulation. In addition, TCTCF could autonomously switch between infrared camouflage and infrared response modes. The radiation temperature of TCTCF was only 34 °C when it was attached to a heating stage at 100 °C. Under simulated sunlight with a power density of 160 mW/cm2, the surface temperature of TCTCF could rapidly rise from room temperature to 83.4 °C. When the applied voltage was 2 V, the surface temperature of TCTCF could rapidly increase from room temperature to 140.2 °C. This work provides a new strategy for the design of polymer-based composites with high EMI SE and low R, and promotes adaptive applications of EMI shielding materials in radar stealth and infrared camouflage.