Temperature-responsive double-network hydrogels with dielectric loss compensation for stable broadband electromagnetic wave absorption

The practical demands of wearable electronics and intelligent flexible devices are driving microwave-absorbing materials toward skin-conformal applications and complex service conditions. Hydrogels show unique advantages in flexible protection owing to their softness, low rigidity and easy adhesion. However, in temperature-fluctuating environments, changes in water state, ion migration, and polarization behavior may lead to unstable dielectric response and even failure of absorption performance. Therefore, on the basis of achieving efficient electromagnetic wave attenuation, further endowing the material with responsiveness to temperature changes and environmental adaptability is an important prerequisite for ensuring its stable microwave absorption performance in dynamic environments. Herein, a temperature-responsive double-network hydrogel was constructed by introducing a P(AM-co-ILs) network, formed through the copolymerization of acrylamide (AM) and an ionic liquid, into a hydroxypropyl cellulose (HPC) matrix. The HPC network provides temperature-responsive behavior, while the polar groups and mobile ions in the P(AM-co-ILs) network offer abundant polarization sites and charge transport pathways, compensating for the weakened dielectric loss caused by water release upon heating. As a result, PT-(HP) 3 achieved an effective absorption bandwidth (EAB) of 6.80 GHz at a matching thickness of 2.25 mm and still maintained an EAB of 6.03 GHz after heating to 45 °C. This work provides a new strategy for designing intelligent flexible microwave-absorbing materials with retained broadband absorption after the thermal phase transition.