Ronald L. Elsenbaumer

Corrosion protection of mild steel by coatings containing polyaniline

Abstract The anti-corrosion performance of polyaniline coated mild steel samples exposed to artificial brine and dilute hydrochloric acid environments was evaluated. Samples of mild steel (UNS G10100) coated with polyaniline deposited from solution, and overcoated with an epoxy barrier paint, when scratched to expose precise areas of bare metal, exhibited corrosion rates in aqueous 3.5% NaCl solutions 2 times less, and in 0.1 N HCl solutions, 100 times less than observed on identical samples coated with epoxy paint alone. Mechanistic information, and quantitative corrosion rates were obtained by Tafel Extrapolation, Potentiodynamic Polarization, Galvanic Coupling and Electrochemical Impedance Spectroscopic techniques. These studies, in conjunction with surface analysis by ESCA and Auger techniques, indicate that the corrosion protection, even for exposed bare steel areas, occurs by the formation of passivating iron oxide (γ - Fe 2 O 3 and Fe 3 O 4 ) surface layers. The formation of these specific oxide layers occurs when the polyaniline is galvanically coupled to the steel. This is evident by the fact that the dimensions of the exposed bare steel area that can be protected in a scratch can be large, but are limited in each corrosion environment.

Processible and environmentally stable conducting polymers

Abstract Highly conducting polythiophene is rendered environmentally stable and solution processible in both its neutral and conductive forms in common organic solvents by appropriate alkyl substitution on the thiophene rings. Solubility increases with increasing chain length of the substituent in the order n-butyl > ethyl ⪢ methyl. Neither the size of the substituent, nor the nature of the dopant has much influence on the conductivity of the doped complexes — typical conductivities are 1–5 ohm −1 cm −1 . Copolymers of thiophenes containing different alkyl substituents were also prepared and were found to exhibit properties similar to the homopolymers. Dialkyl substitution on the thiophene rings gives polymers with less extended conjugation and lower conductivities on doping.

The electronic and electrochemical properties of poly(phenylene vinylenes) and poly(thienylene vinylenes): An experimental and theoretical study

The electronic and electrochemical properties of poly(p‐phenylene vinylene), poly(thienylene vinylene), and their derivatives with electron donating moieties such as methyl, methoxy, and ethoxy are studied using the newly developed electrochemical potential spectroscopy (ECPS) and optical spectroscopy. It is shown that electrochemically derived band gaps agree well with band gap values obtained from optical measurements. Substitution with electron donating groups substantially lowers the ionization potentials and band gaps. A similar effect can be attributed to the incorporation of a vinylene linkage between rings of the polymer backbone. Our results imply that through a proper choice of substituents and backbone structure one can adjust the electrochemical potentials over a wide range as well as red shift the absorption edge of these polymers. In the case of the alkoxythienylene vinylenes the absorption edge is shifted through the visible range of the spectrum into the near infrared (NIR) yielding polyme...

Conducting complexes of polyphenylene sulfides

Poly(p‐phenylene) sulfide, poly(m‐phenylene) sulfide, and the newly synthesized polymer poly(thio‐2,8‐dibenzothiophenediyl) have been treated with strong electron acceptors (AsF5, SbF5) to form conducting complexes with p‐type electronic conductivities up to 3 S/cm. Near IR to UV absorption spectra and temperature‐dependent conductivity measurements suggest a localization of charge carriers even at high doping levels. Elemental analysis and IR spectroscopy demonstrate that heavy exposure to AsF5 causes substantial changes in the backbone structure of these polymers. The dopant appears to predominantly induce the formation of carbon–carbon bonds bridging the sulfur linkages to form thiophene rings. This chemical modification enhances the conductivity of the complex and, in the case of poly(m‐phenylene), is shown to be an actual prerequisite for achieving high conductivity.

Electronic properties of sulfur containing conjugated polymers

Valence effective Hamiltonian (VEH) calculations are performed on a number of sulfur containing organic conjugated polymers of interest to the conducting polymers area. Theoretical results for parameters related to conductivity such as ionization potentials, bandwidths, and bandgaps are presented. Systems considered include various derivatives of poly (p‐phenylene sulfide), polybenzothiophene, and polythiophene, as well as potentially interesting compounds such as polythieno [3,2‐b] thiophene and polyvinylene sulfide. The electronic structure description afforded by the VEH method for sulfur containing polymers is demonstrated to be of the same quality as that presented previously for hydrocarbon polymers. In particular, for ionization potentials, good agreement with available experimental data on poly (p‐phenylene sulfide) and polybenzothiophene is obtained, after scaling downward the VEH values by a 1.9 eV polarization correction. The comparison between the theoretical and experimental XPS spectra for polybenzothiophene is excellent with use of the same energy scaling factor previously employed for polyacetylene, poly(p‐phenylene), and poly(p‐phenylene sulfide). These results, in conjuction with previous results obtained on hydrocarbon polymers, lend confidence in the predictive capabilities of this purely theoretical technique. Calculations show that polyvinylene sulfide, as yet unsynthesized, should display very promising characteristics as a conducting polymer.

The Evolution of Structure During The Alkali Metal Doping of Polyacetylene and Poly(p-Phenylene)

Abstract The progression of phases which evolve during the alkali metal doping of polyacetylene and poly(p-phenylene) is examined using newly developed structure concepts, crystal packing analysis, and diffraction and electrochemical data. At least for alkali metals larger than Li+, at dopant concentrations above a few percent the alkali metal ions aggregate in columns within the host polymer lattice. Structural variations result for polyacetylene both from the degree these columns are filled and the chain-to-column ratio. More limited phase variation results for poly(p-phenylene), where 2,3, and 4 chain/column structures are observed, but the metal-metal spacing within the columns is fixed. Structural models are presented for the 2 chain/column complex of poly(p-phenylene) and the 3 chain/column complexes of K and Rb doped trans polyacetylene.

Protonic acids: Generally applicable dopants for conducting polymers☆

Abstract Non-oxidizing protonic acids have been found to be effective dopants for a wide range of conjugated polymers. A relationship is found between acid strength and ionization potential of a conjugated polymer that will give a highly-conductive doped complex. The mechanism of protonic acid doping appears to involve direct protonation of the polymer backbone followed by an internal redox process that gives polarons as the predominate charge defects. Non-oxidizing protonic acid doping of conjugated polymers now appears to be a general phenomenon that occurs by a mechanism similar to that proposed for protonic acid doping of polyaniline.

Processible, environmentally stable, highly conductive forms of polythiophene

Abstract As electronic materials, the most promising synthetic semiconductors and metals for practical large scale applications are those which can combine convenient processibility with high environmental stability, good mechanical properties, and high conductivity. Missing from the desired combination of properties for the majority of interesting conductive polymers is convenient processibility. A series of solution processible poly(3-alkylthiophenes) are described which form highly conductive, environmentally stable complexes with electron acceptors. These materials are quite unusual in that, in addition to their attractive properties, conductivities are generally high and surprisingly insensitive to the length of the alkyl substituents.

Micro Electromechanical Actuators Based on Conducting Polymers

There is considerable present interest in developing materials technologies suitable for the construction of electromechanical actuators having very small dimensions. The goal is to make the same transition in scale for mechanical devices which has already been made for electronic devices. Since this is a new area, many of the proposed applications are very futuristic — ranging from microrobotic devices for the exploration and repair of the human body to microscopic machines for the manipulation and alteration of micron dimensional objects. More concrete, shorter range goals include such devices as microtweezers, microvalves, micropositioners for microscopic optical elements, and actuators for micromechanical materials sorting (such as the sorting of biological cells).

ELECTRICALLY CONDUCTING POLYAROMATIC SULFIDES.

Abstract Poly(p-phenylene sulfide), PPS, a melt and solution processible polymer, can be made highly conducting by doping with strong electron acceptors such as ASF5. Virgin PPS is an insulator with a relatively high ionization potential compared to polyacetylene. This, coupled with its high melting and solubilization points, restricts possible dopants to those which are particularly aggressive and capable of reacting with PPS in the solid state. These aggressive dopants induce a variety of chemical changes in the polymer backbone upon doping. While fluorination and crosslinking occur to some extent, infrared spectra and independent chemical synthesis suggest that the predominant chemical change is via intrachain bridging (cyclization) of adjacent phenyl rings. In an attempt to find processible systems with lower ionization potentials and which are less prone to chemical modification, a variety of polyaromatic sulfides were prepared. The influence of polymer structure, morphology, and dopant-induced chemi...