Effect of controlled doping on electrical properties and permittivity of PTSA doped polyanilines and their EMI shielding performance

Emeraldine base (EB) has been protonated with different concentration of para-toluene sulfonic acid (PTSA) to form doped polyanilines (PANIs). These samples have been characterized by various techniques and a detailed correlation between dopant concentration and structural, thermal, electrical and electromagnetic properties has been established. The FTIR/UV-Visible and EPR spectra confirm the formation of polarons as proto-generated charge carriers whose concentration follows the dopant concentration trend. It was also observed that increase in doping level leads to systematic improvement of electrical conductivity (1.21^-9 to 5.3 S/cm) as well as complex permittivity (ε'~5.5 & ε″~0.6 to ε'~22.3 & ε″~24.6) with parallel improvement of electromagnetic (EM) radiation blocking capacity from -3.8 dB (for EB) to -23.9 dB (for 1.0 M PTSA doped sample). Further, the attenuation was found to be critically dependent on dopant concentration, complex permittivity and electrical conductivity revealing that both polarization as well as conduction is important for achieving high attenuation. It was also observed that reflection is main phenomenon at low doping level whereas absorption becomes increasingly important at higher doping levels and extends dominant contribution towards total attenuation. (author)