Structure Control of Large-Sized Graphene Foams for Outstanding Microwave Absorption, Thermal Insulation, and Mechanical Stability

With the rapid development of microwave technologies, electromagnetic pollution and stealth have become important problems to be solved. Although great efforts have been made in recent years, it is still a great challenge to achieve strong and broadband absorption combined with thermal and mechanical functionalities. Herein, a multi-functional design toward three-dimensional graphene foams (GFs) is provided. These foams are prepared to have large sizes by simple freezing and air-drying of a structure-integrated graphene oxide (GO) hydrogel, and polydimethylsiloxane (PDMS) is introduced to reinforce the GO framework. The remarkable finding is that the GF/PDMS composite possesses strong broad band absorption (reflection loss < -10 dB) over the entire frequency range of radar microwaves (2-18 GHz). This is attributed to the synergistic effects of dielectric loss of the GO material itself and the multi-layer attenuation brought by the porous foam structure. Experimental results also show that the light foams have very low thermal conductivity of 0.03-0.13 W m(-1) k(-1) and mechanical flexibility for compression, extension, and torsion. Therefore, this study provides a new strategy for large-scale production of multifunctional microwave absorbing foam materials for applications in both civil and military fields.