On metallic characteristics in some conducting polymers

Abstract

Polyaniline (PANI) exhibits a dc conductivity σ ≈ 10 −1 S/cm when it is doped with poly(styrenesulfonic acid) (PSSA) such that the number of sulfonate groups per two-ring PANI unit ( y) is 2. On increasing the dopant amount to y = 12, σ drops to 10 −5 S/cm. The EPR-derived magnetic susceptibility of these two conducting polymers gives nearly the same density of states at the Fermi level N( E F) ≈ 0.65 ± 0.05 states/eV 2-rings. The corresponding electronic specific heat coefficient as calculated from this N( E F) value does not appear to be inconsistent with the results from low temperature calorimetric measurements. Similarly, with y′ defined as the number of sulfonate groups per three-ring PEDOT unit, PSSA-doping of poly(ethylenedioxythiophene) (PEDOT) yields different σ ≈ 10 −1 and 10 −5 S/cm at y′ = 5.7 and 45.9, respectively, but the same N( E F) ≈ 0.55 ± 0.05 states/eV 3-rings. These observations suggest that the additional dopants, which help with dispersion in processing conducting polymers, do not alter the metallic domains but are located in the disordered regions surrounding them. The N( E F) values also remain practically the same between p-toluenesulfonic acid (PTSA) doped PANI and its dispersed blend in poly(methylmethacrylate) (PMMA), as well as for PEDOT–PTSA before and after its being subjected to an additional dispersion step.