Hydro/Organo/Ionogels: "Controllable" Electromagnetic Wave Absorbers

Demand for electromagnetic wave (EMW) absorbers continues to increase with technological advances in wearable electronics and military applications. In this study, a new strategy to overcome the drawbacks of current absorbers by employing the co-contribution of functional polymer frameworks and liquids with strong EMW absorption properties is proposed. Strongly polar water, dimethyl sulfoxide/water mixtures, and highly conductive 1-ethyl-3-methylimidazolium ethyl sulfate ([EMI][ES]) are immobilized in dielectrically inert polymer networks to form different classes of gels (hydrogels, organogels, and ionogels). These gels demonstrate a high correlation between their dielectric properties and polarity/ionic conductivity/non-covalent interaction of immobilized liquids. Thus, the EMW absorption performances of the gels can be precisely tuned over a wide range due to the diversity and stability of the liquids. The prepared hydrogels show good shielding performance (shielding efficiency > 20 dB) due to the high dielectric constants, while organogels with moderate attenuation ability and impedance matching achieve full-wave absorption in X-band (8.2-12.4 GHz) at 2.5 ± 0.5 mm. The ionogels also offer a wide effective absorption bandwidth (10.79-16.38 GHz at 2.2 mm) via prominent ionic conduction loss. In short, this work provides a conceptually novel platform to develop high-efficient, customizable, and low-cost functional absorbers.