Anisotropic structure and electrical properties of intrinsically conducting polymers.

摘要

Two conducting polymers, polyaniline (PANI) and poly(phenylene vinylene) (PPV), were employed in this research to study the relationship between the anisotropic structure and the electrical properties of conducting polymers. The anisotropic structure of the conducting polymers were determined by three independent nondestructive characterization techniques: X-ray diffraction, infrared dichroism, and three dimensional refractive index measurement using a modified prism waveguide coupler. The electrical properties of the conducting polymers were studied by AC impedance spectroscopy.; PPV films fabricated using the precursor route, stretched at 60°C and converted to PPV at fixed length at 200°C at Clemson University, were used for this investigation at Georgia Institute of Technology.{09}Structural study of PPV reveals that the unstretched PPV film has a planar structure, that it is partially crystalline, and that the a axis of the PPV crystal is normal to the film plane. Stretching of the film converts the planar structure to a uniaxial structure; Impedance spectroscopy of the PPV films shows two relaxations, the lower frequency relaxation being related to contact and the higher frequency relaxation being related to the PPV film. Both in-plane conductivity values are higher than the through-plane conductivity.; PANI films were cast from N, N′-dimethyl propylene urea (DMPU) solution and stretched to different draw ratios at Clemson University. X-ray diffraction indicates that the films are noncrystalline and remain noncrystalline after stretching. The neutral PANI, when doped by HCl becomes partially crystalline.; Impedance measurements were made on unstretched and stretched PANI films doped by HCl. For the unstretched film, the impedance of films with different doping level was studied. A conductivity relaxation was observed for both the in-plane measurement and through plane measurement. The relaxation frequency shifts to higher frequency with increasing doping level. The conductivity dramatically increases with doping level and then levels off. The in-plane conductivity is greater than the throughplane conductivity. The impedance of stretched HCl doped PANI films was studied at a fixed doping level. The in-plane conductivity is greater than the through-plane conductivity. The conductivity anisotropy increases with increasing orientation.