Conductive polymer is a type of polymer material that is chemically or electrochemically "doped" from a polymer with a conjugated π bond to convert it from an insulator to a conductor. Its conductive mechanism is generally considered to be doped conductive polymer The carriers are soliton, polaron and bipolaron. The carbon atoms constituting the main chain of the conjugated polymer have 4 valence electrons, of which 3 are a electrons, and the remaining valence electron is a π-electron orbital, which is perpendicular to the plane composed of the polymer. With the expansion of the x system, the energy gap between the π-bonding orbital occupied by electrons and the empty π-antibonding orbital decreases. After doping, an excited state is formed. When subjected to an electric field, the electrons are oriented and polarized to form a current.
Conductive polymers have relatively high conductivity σ and dielectric constant ε, and are easy to control σ and ε through chemical processing. The conductivity can vary within the range of insulators, semiconductors, and metal states. The electromagnetic parameters depend on the main polymer Factors such as chain structure, room temperature conductivity, dopant, degree of doping, synthesis method and conditions. The absorbing performance of conductive polymer is related to its electromagnetic parameters such as dielectric constant, conductivity and other factors. Its absorption of electromagnetic waves mainly depends on electrical loss and dielectric loss. Under the action of radar waves, the conductive polymer is repeatedly polarized on the one hand, and the molecular electric dipole tries to keep up with the field oscillations and is subject to molecular friction. On the other hand, since the conductivity of the material is not zero, induction is formed in the material The electric current generates Joule heat, which causes the electromagnetic wave energy to be dissipated. The good electrical conductivity of the material is conducive to the absorption of electromagnetic waves, but the high electrical conductivity will increase the reflection of electromagnetic waves on the surface of the material. The conductivity of the conductive polymer is easily adjusted by chemical methods, and the best conductivity required by the absorbing material can be obtained.
Since the 1990s, the United States, France, Japan and other countries have successively carried out research on conductive high-altitude radar absorbing materials, envisaged to use them as the "smart skin" for future stealth fighters and reconnaissance aircraft, and for cruise missile hoods. Reversible smart stealth materials, etc. France has studied the radar wave absorption performance of polypyrrole, polyaniline, and poly-3octylthiophene in the range of 0-20 GHz, and found that the absorption performance changes with the frequency of the radar wave. The average attenuation value is -8dB, and the maximum attenuation value can reach -36.5dB, and the bandwidth is 3.0GHz. Successfully prepared a large-area polypyrrole film on a paper substrate by chemical oxidation. The film has good flexibility and exhibits excellent absorption performance and broadband absorption characteristics in the radar wave X band, material impedance and absorption characteristics. The sex changes with frequency and angle of fire. The composite material made by blending polyaniline doped with dodecylbenzenesulfonic acid and ethylene-propylene rubber has a thickness of 3mm, and the reflectivity in the X-band is lower than -6dB, and the peak value reaches -15dB.
As a new type of wave absorbing material, conductive polymer has light weight, good mechanical properties, easy control of composition and structure, wide range of electrical conductivity, and shows strong design adaptability in electromagnetic wave absorption. Earlier studies have shown that the absorption band of a single conductive polymer material is narrow. In order to adapt to the characteristics of high efficiency, broadband, light weight and strong adaptability of future stealth materials, it is necessary to improve the magnetic loss performance of conductive polymers. It is found that the conductive polymer and the inorganic magnetic loss material can be combined to improve the magnetic loss performance of the conductive polymer, so that it has the performance of both electrical loss and magnetic loss, and broadens the absorption band. In addition, when the conductive polymer is placed in the atmosphere, its room temperature conductivity will gradually decrease over time, and the dopant itself is unstable, which also affects the applicable temperature range of the conductive polymer.