Reflectance of conducting polyaniline near the metal-insulator transition

The reflectance spectra of polyaniline protonated with camphor sulfonic acid, PANI-CSA, and with sulfuric acids, PANI-HSO4 are analyzed and compared in deltail. The PANI-CSA reflectance exhibits metallic signatures arising from the free carriers in the partially-filled conduction band, whereas for PANI-HSO4 the data indicate that the states near the Fermi energy (EF) are localized. This localization arises from the severe disorder present in PANI-HSO4, in the context of Anderson localization. For PANI-CSA, however, the counterion-induced processibility results in significant improvement in material quality, leading to more metallic behavior with extended electronic states near EF. Thus, PANI-CSA is a disordered metal on the metal-insulator boundary, in contrast with PANI-HSO4 which is characterized as a Fermi glass.