Showing papers by "Alan J. Heeger published in 1990"

Percolation on a self-assembled network: Decoration of polyethylene gels with conducting polymer.

Abstract: Conducting gels of ultrahigh molecular weight polyethylene and the soluble conjugated polymer poly(3-octylthiophene), P3OT, were prepared by thermoreversible gelation from semidilute solutions in decalin, and subsequent doping with iodine. We report the results of frequency-dependent complex conductivity measurements (from 1 kHz to 1 GHz) on these gels. Although the volume fraction of P3OT in the gel range from less than 5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ to about 3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}2}$, we found evidence of connected conducting paths with no indication of a percolation threshold. The results are discussed in terms of adsorption of the P3OT onto the preformed polyethylene gel network which organizes the P3OT into connected paths at concentrations well below the nominal percolation threshold.

Subnanosecond transient photoconductivity in poly(3-hexylthiophene).

Abstract: Les mesures montrent une reponse photoconductrice rapide, ndependante de la temperature qui decroi←t en 100 ps apres la photoexcitation. La photoexcitation intrachaine des polarons est le processus dominant. L'intensite du photocourant suit le profil d'absorption, en accord avec la photogeneration de porteurs libres via une transition interbande dans un systeme avec des interactions electron-electron efficaces faibles

High performance fibers of conducting polymers

Abstract: We present a summary of our recent results on the electrical and mechanical properties of fibers made from poly(2,5-dimethoxy-p-phenylene vinylene), PDMPV and poly(2,5-thienylene vinylene), PTV, using the precursor polymer methodology, and from polyaniline, PANI, using the method of processing as polyblends with poly-(p-phenylene terephthalamide), PPTA, from sulfuric acid. The solubility of both PANI and PPTA in H2SO4 presents a unique opportunity for co-dissolving and blending PANI and PPTA to exploit the excellent mechanical properties of PPTA and the electrical conductivity of PANI; we summarize the electrical and mechanical properties of such composite fibers. For PDMPV and PTV fibers, we find a strong correlation between the conductivity and the tensile strength (and/or modulus), and we show from basic theoretical concepts that this relationship is an intrinsic feature of conducting polymers.

Percolation of conducting polymers on a gel

Abstract: Fizazi reported evidence of conducting paths at extremely small volume fractions of conducting polymer in a polymer gel ― orders of magnitude below that required for percolation of the soluble conducting polymer alone. An explanation for this phenomenon is proposed

Picosecond photoinduced absorption and polarization memory in polythiophene derivatives.

Abstract: Poly (z-alkyl thiophene)s are studied. Fast bleaching of the interband transition is observed at 2.06eV, accompanied by photoinduced absorption in the band gap at 1.17eV. The results indicate a shift of a fraction of the oscillator strengh, consistent with rapid structural relaxation to form polarons with associated band-gap states. Photoinduced dichroism is observed. The time decay of the polarization memory is consistent with rapid trapping of the initially mobile charged excitations

Process for forming polymers

Abstract: Oriented conjugated polymer shaped articles can be formed by the process of (a) providing a carrier solution made up of (i) carrier solvent, (ii) nonconjugated flexible chain carrier polymer, and (iii) conjugated polymer or conjugated polymer precursor; (b) forming this carrier solution, before or after gelling the solution and removing solvent from it, thereby yielding a body having a first shape, and (c) anisotropically physically distorting the first shape of the body to yield the desired shaped article formed with an oriented structure in the carrier polymer and in the conjugated polymer. The orientation of the conjugated polymer leads to anisotropic absorption and photoluminescence properties for the shaped article.

Self-doped polymers from polyaniline with bronsted acid groups

Abstract: A self-doped conducting polymer having along its backbone a π-electron conjugated system which comprises a plurality of monomer units, between about 0.01 and 100 mole % of the units having covalently linked thereto at least one Bronsted acid group. The conductive zwitterionic polymer is also provided, as are monomers useful in the preparation of the polymer and electrodes comprising the polymer.

Recent Progress in Conducting Polymers: Can We Expect Polymers with Conductivity Greater Than Copper and Strength Greater than Steel?

Abstract: Although improvement of solid state properties through higher quality materials is a general goal of materials science, until recently there had been little optimism that this would be successful for the electrical conductivity of polymers. The reason for this is that, in order to achieve “metallic” behavior, doping to a relatively high level is required; the resulting charged impurities might then be expected to cause scattering and localization. Thus, the need for doping would negate any improvements toward macromolecular chain perfection.

The coupling between electronic structure, geometric structure, and nonlinear optical properties in conjugated materials : the case of linear polyenes

Abstract: This contribution deals with theoretical investigations of the electronic and optical properties of all-trans linear polyenes. The focus is on the geometry relaxation processes occurring in the first singlet, one-photon optically allowed excited state. Calculations are performed at various levels of sophistication, from a simple Su-Schrieffer-Heeger (Huckel-like) Hamiltonian up to Pariser-Parr-Pople single CI and Restricted Hartree-Fock ab initio Hamiltonians. It is found that explicit consideration of the electron-lattice coupling is essential in order to obtain a coherent evolution of the 1Bu state geometry relaxation, in going from short polyenes to long polyenes and polyacetylene. The relevance of our results in terms of the nonlinear optical properties of these compounds is pointed out.