Polymerization and characterization of high conductivity and good adhension polypyrrole films for electromagnetic interference shielding
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Polypyrrole (PPy) shows a favorable application in the electromagnetic interference (EMI) shielding due to its good electrical conductivity and outstanding air stability. Conducting PPy films with high conductivity and good adhesion were successfully polymerized on the surface of insulating epoxy resin substrates using chemical polymerization. The factors affecting the properties of PPy films, such as the surface morphology, adhesion between PPy film and substrate, electrical conductivity, EMI shielding effectiveness (SE), were investigated. The adhesion was improved significantly through a three-step surface pretreatment of epoxy resin substrates including removing impurities, roughening, and surface modification with silane coupling agent. An enhancement in the conductivity of PPy films of about one order of magnitude was achieved by adding dopant in FeCl3 solution. The higher the conductivity, the better the shielding effectiveness. Taking sodium p-toluenesulfonate doped PPy film as example, EMI SE was in the practically useful range of about 30 dB over a wide frequency range from 30 MHz to 1500 MHz. The PPy film samples were characterized by scanning electron microscopy (SEM), infrared spectra (IR), X-ray photoelectron spectroscopy (XPS) and the flange coaxial transmission device. The four-point probe method was used to measure conductivity of PPy films.
KeywordsPolypyrrole film EMI Conductivity Adhesion
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