A temperature-responsive composite for adaptive microwave absorption

Smart microwave absorption (MA) materials with responsiveness to environment are highly desired in modern communication systems, while designing and fabricating high-performance microwave absorbers with adaptivity to working in dynamic service environment is still a challenge. Here we report a temperature-responsive composite composing covalently bonded poly(N-isopmpylacrylamide) (PNIPAAm) and graphene aerogel (GA)for adaptive MA. The dynamic change of hydrogen bonds actuate the conformation change of PNIPAAm chains when the temperature varies below and above the critical transition temperature of 34.8 degrees C, which drives the reduced graphene oxide sheets in GA to delaminate and restacking simultaneously. As a result, the electrical, dielectric and thermal properties of the composite become adaptively switchable. More important, the composite is capable of achieving an effective MA within quite different frequency bands under stimuli of temperature changes. Typically, at 20 degrees C, the effective absorbing band (below -10 dB) ranges from 8.5 to 17.5 GHz, and the minimum reflection loss (RLmin) reaches -32 dB, while when the temperature increases to 50 degrees C, the effective absorbing band shifts to 4.5 similar to 14.0 GHz with the same RLmin. This temperature-responsive composite has great potential of being used as smart devices, especially the advanced electromagnetic protection equipment in the modern communication systems.