Abstract: Carbon-based films with efficient microwave absorption (MA) are highly required in the fields of electromagnetic interference protection and stealth technology due to their low density and high dielectric loss. To obtain desirable MA performance, the loading of carbon fillers is high, easily leading to agglomeration in the polymer matrix and severe deterioration of the flexibility, due to the high specific surface area and strong electrostatic adsorption. Inspired by the important impact of the volume exclusion effect on reducing the filler content in polymer composites, the introduction of microwave transparent phases can effectively improve the impedance matching, resulting in excellent MA performance at low filler loading. Herein, a simple vacuum-assisted filtration method was proposed to fabricate flexible aramid nanofiber films. This work makes full use of the volume exclusion effect of microwave-transparent hollow glass microspheres to obtain ideal dielectric loss at the low loading of carbon fillers. The resultant films present excellent MA performance and environmental adaptability. With only 2 wt % graphene, the film exhibits a minimum reflection loss (RL_min) of -60.84 dB and a wide effective microwave absorption bandwidth (EAB) of 6.44 GHz. Impressively, we found that the size of microwave-transparent phase has an important influence on the MA performance of the films through the experimental results and electromagnetic simulations. This method offers a promising approach for developing high-performance MA polymer composites in the future.

Key words: Lightweight, Volume exclusion effects, Electromagnetic simulations