Polyaniline Electrochemical Preparation And Mechanism Of Electromagnetic Shielding Composite Materials Research

Conducting polyaniline(PANI), as one of the most important conducting polymers, has been intensively prospective recently due to its adjustable conductivity, ease of preparation, good environment stability, and a large variety of applications. But the conductivity of PANI is not very high and the processing of PANI is difficult for its insolubility. In this paper, the processing can be improved by compositing with polymer, and it acquire a higher conductivity while doped by proton acid and composited with metal. The high conductive composite film can applied in electromagnetic shielding materials. This work includes the three aspects:1) The synthesis of conductive PANI co-doped by5-sulfosalicylic acid(SSA) and sulfuric acid(H2SO4) has been achieved using electrochemical method in PVA supporting film. The optimum conditions of deposited silver on the conductivity of composite films were also studied. The characteristics of PVA/PANI and PVA/PANI/Ag composite films were studied by X-ray diffraction(XRD), scanning electron microscope (SEM), infrared ray(IR). The results show that the optimum conductivity of composite film can be obtained to22.72S·cm-1.The conductivity of film is increased to13558·cm-1significantly for deposited silver. Through appropriate degree of tension for the PVA/PANI and PVA/PANI/Ag composite films, the conductivity can be enhanced to20.74%and18.04%respectively. The composite films exhibits excellent mechanical properties. IR spectra showed the existence of sulfonic group, which proved5-sulfosalicylic acid had been doped in PANI. The composite films have crystallinity to some extent, and can be improved after tensile. PVA/PANI is fibrous morphology and Ag is acicular covered on or inlaid among the fibers of PANI.2) The synthesis of conductive PANI co-doped by5-sulfosalicylic acid(SSA) and sulfuric acid(H2SO4) has been achieved using electrochemical method in PTFE supporting film. The optimum conditions of deposited silver on the conductivity of composite films, tensile and heat treatment for the conductivity and mechanical properties of composite films were also studied. The characteristics of PTFE/PANI and PTFE/PANI/Ag composite films were studied by Raman spectroscopy, scanning electron microscope(SEM), TG, X-ray diffraction(XRD) and infrared ray(IR). The electromagnetic shielding of series of PTFE composite films was also studied. The results show that the optimum conductivity of composite film can be obtained to36.9S·cm-1.The optimum conductivity of film is increased to5379S·cm-2significantlyfor deposited Ag. Through appropriate tension for PTFE/PANI and PTFE/PANI/Ag composite films, the conductivity can be enhanced to19.74%and38.33%respectively. The composite films show excellent mechanical properties. The conductivity of PTFE/PANI composite film dropped by heat treatment from80℃to180℃in air and vacuum atmosphere, so did the conductive of PTFE/PANI/Ag composite film in air. The mechanical strength of the series of composite films changed less, while the ductility reduced dramatically. The conductivity of PTFE/PANI/Ag composite film got a maximum in vacuum at120℃, and its mechanical strength improved while ductility reduced. Raman spectroscopy showed PANI, Ag and PTFE compound well. PANI is small pellet, Ag is dentrites covered on or inlaid among the grains of PANI to forming three-dimensional conductive network. The weightlessness of the series of composite films is minor at the temperature from100℃to180℃. The composite films have crystallinity to some extent, and can be improve after tensile, the crystallinity of PTFE/PANI film is lower after heat treatment at180℃in air. The results of IR spectrum show5-sulfosalicylic acid has dedoped from PTFE/PANI composite film, and benzene rings have transformed into quinone by thermal oxidation. At the same time, thermal oxidation also caused the molecule chain of PANI broken and cross-linking, therefore the conductivity of the films decreased. The shielding effectiveness of PTFE/PANI composite film is from16dB to24dB, while PTFE/PANI/Ag composite film is from35dB to70dB which indicates it has good shielding effect.3) The composite deposited mechanism of composite film had been investigated by cyclic voltammetry(CV) curve. The conductive model and shielding model of composite film were designed to explaine the conductive and shielding mechanism. The mechanism of electromagnetic shielding of4kinds of composite films were studied by CV and Electrochemical Impedance Spectroscopy(EIS). The potential indicates the dope process of PANI by H2SO4in PVA is easier than that of co-doped by H2SO4and SSA, but the stability of PANI is worse than that of co-doped; The potential of depoed for PANI is more negative than that of reduction for Ag, so the deposited Ag on PANI can not decrease the conductivity of PANI composite film. The potential of PANI doped by H2SO4in PTFE indicates the dope process of PANI by H2SO4is easier than that of co-doped in PTFE by H2SO4and SSA, but the stability of PANI is worse than that of co-doped; the deposited Ag on PANI can not decrease the conductive of the composite film. The conductive model shows PANI connected with each other in the support film and formed conductive pathway, silver covered on and inlaid in PANI composite film which formed three-dimensional network. The shielding model shows the conductivity, thickness and dense of PANI/Ag composite film are higher than that of PANI composite film because of silver inlayed and covered, and the reflection and absorption of electromagnetic wave were enhanced. The results of CV and EIS show that PANI composite film not only shows resistance property, but also capacitive and inductance property for its distinguishing quality of redox.