Highly Flexible Hydrogels with Readily Adjustable Electromagnetic Parameter for Efficient Electromagnetic Wave Absorption

In the past, hard electromagnetic wave (EMW) absorbing materials have made breakthroughs in performance improvement, but poor machinability limits their practical applications. Herein, a series of flexible borate ester bonded hydrogels with different water content for EMW absorption were prepared through a simple ultraviolet curing method. By adjusting the water content, the EMW absorption performance of hydrogel can be improved. When the water content reaches 30%, the minimum reflection loss (RL min ) of the hydrogel can be up to −48.70 dB at 1.89 mm and the widest effective absorption bandwidth (EAB w, RL ≤ −10 dB) is 5.60 GHz (covering the entire Ku band) when the matching thickness is between 2.09 and 2.17 mm. The efficient absorption performance of the hydrogel benefits from the dipole polarization of water molecules and the interfacial polarization caused by interaction with the polymer network framework under the changing electromagnetic field. In addition, tensile and compressive experiments show that the hydrogel possesses favorable flexibility. This study provides an idea for the preparation of flexible electromagnetic attenuation devices, and the as-synthesized hydrogels have a broad application scenario in the field of wearable EMW-absorbing materials.