Polyimide composite aerogels towards highly efficient microwave absorption and thermal insulation

Magnetic enhanced high-efficiency electromagnetic wave absorbing MXene/Fe3O4 composite absorbers at 2–40 GHz

“…In general, a larger impedance matching ratio between the absorber and the free space ( Z = | Z in / Z 0 |) indicates that the material has a stronger EMW absorption performance, 59 which reduces the interface reflection as much as possible, and can reach zero reflection when Z is close to 1, 60 and the favorable absorbing performance will be realized. 61 Fig.…”

“…It reveals that the values of the dielectric loss are much higher than those of the magnetic loss in the high frequency regions, indicating that the absorber is mainly dependent on the dielectric loss. 57,58 In general, a larger impedance matching ratio between the absorber and the free space (Z = |Z in /Z 0 |) indicates that the material has a stronger EMW absorption performance, 59 which reduces the interface reflection as much as possible, and can reach zero reflection when Z is close to 1, 60 and the favorable absorbing performance will be realized. 61…”

Microwave-Assisted Foaming of Mechanically Robust Lightweight Polyimide Foams with Anisotropic Pore Structures for Thermal Insulation Applications

“…Theoretically, thermal conduction consisted of three aspects, i.e., thermal conduction, convection, and radiation. In general, the λ of porous materials include gas phase conduction (λ cond g ), solid phase conduction (λ cond s ), thermal convection (λ conv ), and thermal radiation (λ rad ), , which can be expressed by the following equation: λ = λ cond normalg + λ cond normals + λ conv + λ rad …”

“…Convection is the macroscopic movement of the fluid, gas convection requires pore sizes larger than 10 mm, and λ conv is negligible for PIFs with a 3D pore structure (pore diameters less than 200 μm). , In addition, λ rad is only considered at high temperatures and under vacuum conditions , 3 . Thus, the effective thermal conductivity (λ eff ) of PIFs depends on λ cond g , λ cond s and λ rad , which can be estimated using the following simplified equation: λ eff = λ cond normalg + λ cond normals + λ rad …”

Optimizing impedance matching and interfacial characteristics of aromatic polyimide/graphene by molecular layer deposition for heat-conducting microwave absorption

“…[19][20][21] Considering that polyimide (PI) has the advantages of a light weight, high temperature resistance, and chemical corrosion resistance, it can be used as a tunable component to compound with graphene. [22][23][24][25] On the one hand, the introduction of PI can improve impedance matching, optimize interfacial characteristics and eventually improve microwave-absorption performance. On the other hand, the dispersibility in the polymer matrix can be ameliorated, and the effective phonon transfer in the heat-conduction channel of the material can be enhanced, ultimately reducing the interfacial thermal resistance.…”