Electromagnetic interference shielding of polypyrrole nanostructures

Polypyrrole (PPy) is an electrically conductive organic material perspective for application in the field of electromagnetic interference shielding (EMI). The presented fundamental study focuses on the shielding efficiency of three various morphologies of PPy (globules, nanotubes and microbarrels). Powdered samples in both protonated and deprotonated form were embedded at various concentrations (1, 3 and 5 % w/w) in a composite system with a transparent silicone matrix cured at temperatures 25 and 150 degrees C. The ability of PPy to reflect or absorb electromagnetic radiation in the C-band region covering the range from 5.85 to 8.2 GHz was evaluated. The relationship between the morphology of PPy, its DC and AC electrical conductivity, permittivity and shielding efficiency was studied. The PPy nanotubes with the DC conductivity of 60.8 S cm(-1) exhibited shielding efficiency S-21 = -13.27 dB at 5% w/w concentration in the composite, which corresponds to transparency of 21.7 % only. It was found that the magnitude of electrical conductivity together with the aspect ratio of PPy morphology determines the shielding efficiency whereas the type of morphology is responsible for absorption or reflection mechanism of EMI shielding. Hence, the appropriate adjustment of both the electrical conductivity and the morphology should be used in the future lightweight and flexible EMI shields with tunable shielding efficiency and mechanism of shielding.