Tunable microwave absorption of anisotropic hydrogels induced by an electric field

This study demonstrates an electric-field-induced self-assembly strategy for fabricating smart iron complex-gelatin hydrogels. By applying a direct current (DC) electric field during the gelation process, gelatin/polyvinyl alcohol (PVA) interpenetrating network hydrogels containing organic iron complexes (EDTA-Fe and COS-Fe) were fabricated. The results reveal that an external electric field effectively polarizes the functional groups within the hydrogel, thereby transforming its microscopic network from a disordered state into an ordered, anisotropic structure aligned along the electric field direction. This structural ordering induces the formation of abundant heterogeneous interfaces, which significantly enhances dielectric loss via Maxwell-Wagner interfacial polarization and improves impedance matching. Consequently, the hydrogels exhibit reinforced mechanical properties and excellent microwave absorption performance. Specifically, the COS-Fe-loaded hydrogel (PGC) exhibits superior electromechanical responsiveness (Δ G = 4.13 kPa, ρ = 20%), whereas the EDTA-Fe-loaded hydrogel (PGE) demonstrates stronger tunable microwave absorption, achieving an optimal minimum reflection loss ( RL ) of −33.0 dB at 2.86 GHz under an electric field of 1.6 kV/mm.