The Research On Preparation And Electromagnetic Characters Of Polyaniline

In this paper, conducting polyaniline(PANH) doped with hydrochloric acid(HCl) andpolyaniline/manganese dioxide composites(PANH/MnO₂) are synthesized by a chemicalpolymerization method, respectively. The mircrostructure and morphology of specimen arecharacterized by means of Fourier transform infrared (FT-IR), ultraviolet spectrometer (UV),X-ray diffraction spectroscopy (XRD), Transmission electron microscope (TEM), Scanningelectronic microscope (SEM), thermogravimetric analysis (TGA) and differential scanningcalorimetry (DSC). The conductivity and electromagnetic property of the specimen arestudied, as well as the environmental stability of PANH is investigated.The analysis results indicate that polyaniline has better doped character. The PANHsynthesized by chemical oxidation process performs a certain degree of crystallinity anddistributes as spheric shape. Increased crystallinity can imporove conductivity. Dopedpolyaniline exhibits excellent elecrtic conductivity and electromagnetic properties bycompounded with silicone rubber. When the mass fraction of PANH in polyaniline/siliconrubber composite is reaching 50 wt.%, the DC conductivity reaches 1.93 s/cm and the averageelectromagnetic interference shielding effectiveness reaches -26dB in the frequence range of0.13～1.5GHz, which is a good civilian shielding materials. The PANH is dielectricdissipation material that has excellent electromagnetic (EM) absorbing property in thefrequency range of 2～18GHz. Using the transmission lines principles, the calculation valueof EM absorption shows that the PANH/MnO₂ composite slab with 2mm thickness and 40wt.% PANH has the best absorption property and the effective absorption bandwidth(＞10dB) reaches 3GHz.Compound particles of PANH/MnO₂ containing different amounts of MnO₂ aresynthesized by in-situ polymerization process. The results indicate the conductivity anddielectric constant of compound particles decrease with increasing mass ratio loading ofMnO2, which can be markedly improved by post-processing immersing inaniline-hydrochloric acid solution. The measuring results of electromagnetic contant showthat the compound particle is dielectric loss materials, because of both the real partε' andthe imaginary partε" of permittivity show significant variation with increasing frequency.EM absorption by calculation of particles/paraffin composite slab is noticeably improved thanpure polyaniline/paraffin composite slab and the effective frequency bandwidth reaches 5 GHz. Therefore, it is meaningful to be satisfy with modern absorbing requirements of "Thin,Light, Wide, Strong " that the preparation of electromagnetic wave absorbing materials byusing the synergism effect between polyaniline and MnO₂ and improving the processingtechnology of composite.In order to obtain the best stability parameters of polyaniline, the effect of differentthermal treatment temperature on the microstructure and electric properties of polyaniline isinvestigated under air atmosphere. The results show that HCl-doped polyaniline (PANH)prepared by in-situ polymerization solution displays excellent electrical conductivity anddielectric properties when the temperature is under 100℃. The effect of thermal treatment onthe conductivity and the dielectric characteristics of PANH are mainly attributable to theevolution of dopant and the changes in the molecular structure.