J. Joo

Charge transport of camphor sulfonic acid-doped polyaniline and poly(o-toluidine) fibers: role of processing

Abstract We report the results of transport studies (temperature-dependent d.c. conductivity, thermopower, microwave frequency conductivity and dielectric constant for camphor sulfonic acid-doped polyaniline (PAN-CSA) and its methyl ring-substituted derivative, poly( o -toluidine) (POT-CSA) fibers prepared in solutions of m -cresol. The results for the PAN-CSA fiber are very similar to those for PAN-CSA film with the presence of some poorer conducting linkages. The POT-CSA fiber shows significantly higher conductivity with much weaker temperature dependence than the earlier studied hydrochloric acid-doped poly( o -toluidine) (POT-HCl) fiber and powder, indicating that it is much closer to the localization-delocalization boundary.

Evolution of the conducting state of polyaniline from localized to mesoscopic metallic to intrinsic metallic regimes

Abstract The results of microwave dielectric constant (ϵmw) and dc conductivity (σdc) of doped polyaniline (PAN) samples in different charge delocation regimes are reported. With camphor culfonic acid doped PAN prepared in m-cresol solvent (PAN-CSA (m-cresol)) respresenting the most delocalized material, a negative ϵmw is measured indicating an intrinsic metallic state. The Drude model at low frequency is used to estimate a relatively small plasma frequency ω p ⋍ 0.015 eV and an anomalously long scattering time τ ⋍ 1.2 × 10−11 s. This τ implies the importance of phonon back scattering for the most delocalized electrons as expected for the open Fermi surface of a highly anisotropic metal. Depending on the crystallinity, there are two different charge localization regimes in PAN samples: uncoupled metallic islands and coupled “mesoscopic” metallic state. The three-dimensional nature of metallic state is demonstrated by the correlation of low temperature dielectric response with the parallel and perpendicular crystalline domain lengths obtained from x-ray data. The charge localization to delocalization transition dependence on the polymer processing will be discussed. We present the temperature dependent nonmetal-metal transition for some preparations of PAN-CSA (m-cresol). The intrinsic conductivity of metallic PAN is estimated to be ∼ 107 S/cm.

Polyanilines: Recent Advances in Processing and Applications to Welding of Plastics

Polyanilines have been known for over 100 years. Recent studies have demonstrated unusual chemical, electrical and optical phenomena in both the insulating and the conducting forms. Advances in the chemistry of polyanilines have lead to improved processibility leading to highly conducting oriented films and fibers. We briefly review here the chemical states of the polyanilines as well as the suggested applications of polyanilines and other conducting polymers. Emphasis is given here to the new concept of secondary doping as a means to enhance conductivity and other properties; also emphasized here is the use of conductive polyaniline as a means of remote welding (joining) of insulating plastics. This novel latter approach results in joints that, in some cases, are as strong as the materials being bonded.

The Metallic State of Conducting Polymers: Microwave Dielectric Response and Optical Conductivity

Recent advances in processing of polyaniline and polyacetylene have resulted in a new generation of conducting polymers with higher dc conductivities. We present the temperature (T) dependent microwave frequency dielectric constant, dc conductivity, and Kramers-Kronig analysis of conducting polyaniline and polyacetylene. The low temperature dielectric constant, e, increases with the square of the x-ray crystalline domain length for preparations of HCl protonated polyaniline. For the highest crystalline polyaniline samples, e increases dramatically with increasing T, supporting formation of three-dimensional (3-D) coupled “mesoscopic” Metallic regions. A “metallic” negative e is observed for d,1-camphor sulfonie acid doped polyaniline prepared in m-cresol. Optical studies show a linear increase in reflectivity below 7000 cm -1 . Below 600 cm -1 the reflectance increases rapidly. Kramers-Kronig analysis of the ir-visible results are presented. Highly conducting polyaniline is shown to have two plasma frequencies, one at ∼ 1.1 eV involving all the conduction band electrons, and one at ∼0.015 eV (120 cm -1 ) that is suggested to arise from the most delocalized electrons. The concept of inhomogeneous disorder is introduced. The results for polyaniline are compared to those of highly doped polyacetylene which also show metallic negative e demonstrating the intrinsic metallic nature of the new generation of conducting polymers.

Conductivity and microwave dielectric response of polyaniline and poly(o-toluidine) fibers

Abstract We compare the results of temperature-dependent de conductivity σ dc ( T ) and microwave dielectric constant ϵ mw ( T ) for CSA doped polyaniline (PAN-CSA) and poly( o -toluidine) (POT-CSA) fibers prepared in m -cresol, HCl doped 4-fold stretched polyaniline EB fiber (PAN-HCl(4X)), and HCl doped poly( o -toluidine) (POT-HCl) fibers (unstretched and 3-fold stretched). Although POT-HCl fibers show similar σ dc ( T ) as earlier studied POT-HCl powder, POT-CSA fiber shows significantly higher σ dc ( T ) with much weaker temperature dependence and much larger ϵ mw ( T ), indicating that it is much closer to the localization-delocalization boundary. PAN-HCl(4X) fiber and PAN-CSA fiber have almost identical dc conductivity at room temperature, however PAN-HCl(4X) fiber shows stronger temperature of σ dc and a very large positive ϵ mw , as opposed to have huge negative ϵ mw observed in the PAN-CSA fiber.

Weak localization, electron-electron interaction, and metal-insulator transition in ion-implanted polymers

Abstract Kr + ion implanted rigid rod PBO, PBT and ladder BBL polymers show similar transport and optical behavior, with room temperature conductivities increasing from 10 −12 S/cm to ∼ 10 2 S/cm after implantation. A metal-insulator transition is observed at T c ∼ 30 K. Above T c , the results of a negative magnetoresistance ( ΔR / R ( H , T )), a weakly temperature dependent conductivity ( σ ( T ) α T p , 0.5 p T -dependent thermopower ( S ( T )), a Pauli spin susceptibility ( χ Pauli ), and a large microwave dielectric constant ( e mw ) resemble those of disordered metals in which weak localization and e-e interactions dominate the charge transport. Below T c , the changed behavior of positive ΔR / R , stronger T -dependent σ , and 1/ T -dependent S with a continued large and positive e mw all suggest an increased e-e interaction effect which opens up a ‘Coulomb’ gap (∼2meV), likely due to the enhanced localization. The density of states (DOS) is zero only at the center of the gap in accord with the theoretical prediction of the ‘Coulomb’ gap.