Light-triggered conformable dynamic hydrogels for dopant-free electromagnetic wave absorption

Electromagnetic waves (EMWs) underpin modern functional devices, yet raise safety concerns across biological, military, and civilian domains. While polymers feature softness and light weight, their intrinsically weak interaction with EMWs necessitates dopant incorporation for wave attenuation and they often lack the ability to dynamically conform to shielded objects. Here, we report a disulfide crosslinked amphiphilic hydrogel to directly absorb electromagnetic waves, forgoing the need for dopants. This capability stems from water-induced phase separation, which creates abundant polymer-liquid interfaces and free water throughout the material. The resulting reflection loss and electromagnetic wave absorption bandwidth reach -33 dB and 2.9 GHz at 2.0 mm, respectively, outperforming the present absorption hydrogels. Besides, the mechanical toughness is enhanced to 5.5 MJ m^-3 through hydrophobic aggregation. Moreover, the hydrogel retains high transparency and can be dynamically programmed into versatile shapes via light-triggered disulfide bond exchange, enabling conformal attachment to arbitrary objects. With high reflection loss and shape programmability, the hydrogels are employed in wearable and optical devices for daily EMW protection. The versatility of our strategy paves the way for the future EMW shielding materials with diverse functionalities.