Lightweight bacterial cellulose-based composite foams with multilayer structure for low-reflection EMI shielding and switchable infrared camouflage

As electronic devices and communication technologies continue to advance, the issue of electromagnetic pollution has become more pronounced. Consequently, there is an urgent requirement for electromagnetic interference (EMI) shielding composites characterized by a low reflection coefficient (R). In this work, MXene/graphene oxide/bacterial cellulose (BC) composite foams (MGCF) featuring a multilayer structure were successfully constructed via layered freezing combined with freeze-drying technology. The multilayer structure of MGCF effectively attenuates electromagnetic waves (EMWs) through a synergistic effect. Specifically, the top impedance matching layer guides EMWs into MGCF, the intermediate absorption layer dissipates the majority of electromagnetic energy as heat via dielectric loss, and the bottom highly conductive reflection layer reflects the transmitted EMWs back to the middle absorption layer. Through this sequential ‘matching–absorption–reflection’ mechanism, electromagnetic energy is thoroughly attenuated, leading to outstanding EMI shielding performance coupled with a minimized R. Due to its unique multilayer structure, MGCF exhibits an EMI shielding effectiveness (SE) of 54 dB, maintaining the R value within the range of 0.22 to 0.38. Moreover, MGCF exhibits an exceptionally low thermal conductivity (λ) of merely 59.58 mW·m^–1·K^–1, meeting insulating requirements. Additionally, MGCF can autonomously transition between infrared stealth and infrared response states. The surface temperature of the MGCF during the hot stage at 100 ℃ is only 44.3 ℃. When exposed to simulated solar irradiation at a power density of 120 mW·cm^–2, the surface temperature of the MGCF swiftly increased from ambient temperature to 69 ℃. This work presents a novel approach to designing biopolymer composites with excellent shielding performance and minimal reflection, and accelerates the evolution of EMI shielding materials designed for adaptive applications, particularly in radar stealth, infrared camouflage and thermal insulation.