ANISOTROPIC OPTICAL-PROPERTIES OF AN ORIENTED-EMERALDINE-BASE POLYMER AND AN EMERALDINE-HYDROCHLORIDE-SALT POLYMER

We present results of polarized reflectance measurements for unstretched and stretched films of polyaniline in the insulating emeraldine-base (EB) and conducting emeraldine-salt (ES) forms. The reflectance data and the resulting optical conductivity, obtained from a Kramers-Kronig transform of the reflectance data, of unstretched films agree well with optical data reported by S. Stafstrom et al. [Phys. Rev. Lett. 59, 1464 (1987)]. The stretched films (400% elongation) show significant anisotropy in the reflectance and the other optical constants. The frequency-dependent conductivity in ES exhibits a large shift in oscillator strength to lower energies compared to that of EB and compared to that of unstretched films of ES, which demonstrates delocalization of conduction electrons in the ''polaron band.'' The dielectric constant of stretched ES indicates that ES is metal-like, with maximum conductivity greater than ten times the dc conductivity. These results indicate that the dc conductivity is likely dominated by interchain processes and that higher values of conductivity are possible.