Preparation And Microwave Absorption Properties Of Chiral Polyaniline And Its Composites With Inorganic Absorber

Radar absorbing material (RAM) is the important basis of radar stealth used inmodern aircraft, weaponry etc. With rapid development of modern detection technologyand continuous updating application of detection equipment, combat equipments face ahuge threat. Currently the traditional absorbing materials have been continuouslyapplied, and the research of RAM has made some progress. However, the RAM still hassome problems, such as a narrow absorbing band, low absorption intensity and badenvironmental stability. In order to increase the probability survival of combatequipment and improve the penetration performance of combat equipment, we have toresearch and develop new RAM with new mechanisms of absorbing basis on traditionalabsorbents.The electromagnetic theory and microwave absorbing mechanism were analyzed.In this paper, we used the unique absorbing properties of new polymeric radar absorbingmaterial (chiral PANI) to modify the traditional absorbents, and developed newcomposite absorbing materials such as chiral PANI, chiral-PANI/SiC composite andchiral-PANI/PVP/CIP composite. The characterization of the composites was discussedwith the electronic scan electric mirror (SEM), infrared spectrum (FT-IR), ultravioletspectrum analysis (UV-Vis), X-ray diffraction (XRD), electrochemical workstation,four-point probe conductivity measurements, TGA thermogravimetric analyzer andvector network analyzer (VNA). The influence of properties of composite radarabsorbing material was discussed by the microstructure, structure, and electromagneticperformance. According to the transmit line theory, the reflection loss (RL) of thecomposite was calculated. The result shows that the RAM of chiral PANI and itscomposite with better impedance matching of microwave absorbing properties wereprepared.The major contests and conclusions are as follows:(1) Chiral polyaniline (PANI-(D-CSA)) doped with D-camphorsulfonic acid(D-CSA) was synthesized by in-situ polymerization in the presence of a constantmagnetic field (0.4T). The influence of magnetic field to the microstructure,conductivity, electromagnetic property of PANI-(D-CSA) was discussed. The researchshows that the presence of a magnetic field can significantly improve the chiral degree,electrical conductivity and dielectric and magnetic losses of PANI-(D-CSA) which therefore shows better electromagnetic wave loss ability. Magnetic field takessignificant impacts on the radical PANI synthesis and conduces to the generation oftriplet radicals, which will make the molecular chains of the polymerization productlonger and more orderly arranged. The presence of magnetic effect significantlyincreases the microwave absorption ability of PANI-(D-CSA). The minimal reflectivityis reduced by21.77%and the bands below-10dB increases4.7times by contrast withthe absence of magnetic effect.(2) Chiral-polyaniline (chiral-PANI)/silicon carbide (SiC) composites wereprepared for the first time by emulsion polymerization using sodium dodecylbenzenesulfonate (D-CSA), ammonium persulfate (APS) as an emulsifier and oxidant,respectively. The structure and micro-morphology of SiC and chiral-PANI/SiCcomposites were characterized by UV-Vis, FTIR, XRD and SEM. The thermal stabilitywas tested by the TGA. The electromagnetic parameters and microwave absorbingproperties were measured by vector network analyzer (VAN) at26.5-40GHz. Theresults show that the UV-Vis, FTIR and XRD results indicated that there existed aninteraction between chiral PANI molecules and SiC particles; the SEM results indicatedthat SiC particles were covered with the chiral PANI; the content of chiral PANI in thePANI/SiC is31.6%of the TGA test. The relative complex permeability and the relativecomplex permittivity were determined using a vector network analyzer (AgilentE8363B) in the range of26.5-40GHz by Niolson Ross rectangular waveguide method.Compared with the pure SiC absorbent, the minimum RL of chiral-PANI/SiC compositeis-21.53dB; and the effective absorption band under-10dB reached8.10GHz.Obviously, after the SiC modified by chiral PANI, the absorption efficiency wassignificantly improved, and the absorption band was also broadened(3) The chiral polyaniline/polyvinylpyrrolidone/carbonyl iron powder(chiral-PANI/PVP/CIP) core-shell composites were prepared by in-situ polymerizationin the PVP aqueous solution using toluenesulfonic acid (D-CSA) as dopant andammonium persulfate (APS) as oxidant. The chiral-PANI/PVP/CIP composite wassystematically investigated using scanning electron microscopy (SEM), FT-IRspectroscopy, electrochemical workstation, thermogravimetry analysis (TGA) andvector network analyzer. And the mechanism of PVP in the polymerization process wasdiscussed. The results showed that long polymeric chain can sterically hinder theaggregation among CIP molecules, and PVP provides a protective overlayer on CIP thatslows oxidation by APS, due to the surface modification. By calculating the measured electromagnetic parameters, the effective absorption band of chiral-PANI/PVP/CIP under-10dB reached11.3GHz (28.7-40.0GHz), and the minimum RL of-19.29dB whichobserved at29.5GHz. It can be widely used in wideband radar stealth.The results in this paper show that the chiral structure and core-shell structure ofchiral PANI and its composites are significant effect to the electromagnetic waveabsorption properties, and beneficial for the reflection, scattering and absorption ofmicrowave. The research has important guiding significance, and can provide a newapproach to develop high-performance absorber.