Microwave transport in the emeraldine form of polyaniline

The conductivity and dielectric constant of the emeraldine polymer are studied at a frequency of 6.5×${10}^9$ Hz as a function of temperature T and protonation levels spanning from insulating emeraldine base [${\sigma }_{\mathrm{dc}}$(295 K)≊${10}^{\mathrm{-}9}$ (Ω cm${)}^{\mathrm{-}1}$] to conducting emeraldine salt [${\sigma }_{\mathrm{dc}}$(295 K)≊${10}^0$ (Ω cm${)}^{\mathrm{-}1}$]. The microwave conductivity is larger than the dc conductivity by many orders of magnitude for the base but approaches that of dc for more conducting emeraldine salts. For lowly protonated emeraldine polymers the dielectric constant is small and almost temperature independent. For higher protonation levels the dielectric constant is linear in T with deviations observed at maximum protonation level. The dielectric constant increases monotonically with protonation for intermediate and higher-level protonated emeraldine salts. The temperature dependence of microwave conductivity differs from that of dc, especially at lower temperatures. In general, the data support the phase segregation of polymer into ‘‘metallic islands’’ and insulating background with localization prevailing at low temperatures. In view of the presence of barriers within the metallic islands and the increase of coherence length of the charge carriers with temperature, the phrase of ‘‘textured metallic islands’’ is introduced to describe the delicate role of temperature on the interplay between localization and delocalization. We review the relevance of some of the transport models to emeraldine polymers.