Dennis E. Tallman

Direct Electrodeposition of Polypyrrole on Aluminum and Aluminum Alloy by Electron Transfer Mediation

The direct electrodeposition of electroactive conducting polymers on active metals such as iron and aluminum is complicated by the concomitant metal oxidation that occurs at the positive potentials required for polymer formation. In the case of aluminum and its alloys, the oxide layer that forms is an insulator that blocks electron transfer and impedes polymer formation and deposition. As a result, only patchy nonuniform polymer films are obtained. Electron transfer mediation is a well-known technique for overcoming kinetic limitations of electron transfer at metal electrodes. In this work, we report the use of electron transfer mediation for the direct electrodeposition of polypyrrole onto aluminum and onto Al 2024-T3 alloy. This report focuses on the use of Tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt) as the mediator, although catechol appears to function in a similar manner. Depositions were carried out under galvanostatic conditions at current densities of I mA/cm 2 . The mediator reduced the deposition potential by nearly 500 mV compared to deposition performed in the absence of mediator (where Tiron was replaced by p-toluene sulfonic acid sodium salt). Polypyrrole formation and deposition appears to occur with 100% current efficiency and uniform films are obtained. Results of the characterization of these films by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, conductivity measurements, and adhesion measurements are presented.

Electron transfer mediated deposition of conducting polymers on active metals

New methods for directly depositing conducting polymers onto active metals (such as aluminum and its alloys) are being developed. The methods employ electron transfer mediation to lower the potential for polymer electrodeposition, thus avoiding concomitant oxidation of the metal and resulting in current efficiencies of nearly 100%.

Preparation and preliminary characterization of a poly(4-vinylpyridine) complex of a water-soluble polyaniline

Abstract A polymer complex between a sulfonated water-soluble polyaniline (SPANI) and poly(4-vinylpyridine) (PVP) is formed by mixing an aqueous solution of the protonated (hydrogen chloride) form of PVP, a cationic polyelectrolyte, with an aqueous solution of SPANI. A gel-like precipitate forms which has limited solubility in many common solvents. Thus, the approach represents a possible route to the aqueous solution processing of polyaniline. The nitrogen-to-sulfur ratio of the complex indicates approximately a 1:1 stoichiometry between PVP and SPANI monomer units. The complex exhibits modest conductivity (3.3 × 10 −5 S/cm) and is electroactive when immobilized on carbon or platinum electrodes. The swellability of the gel form of the complex is characterized by a solvent content of 16 grams per gram of dry material. Thermal analysis of the dry complex indicates stability to 225 °C.

Deposition of Polypyrrole on Porous Aluminum Oxide

Aluminium (Al) alloys, such as Al 2024-T3, are extensively used in the aircraft industry because of their light weight and excellent mechanical properties. Chemically pure Al is naturally protected from corrosion by an oxide layer. In the case of alloys this layer contains intermetallic impurities capable of causing galvanic corrosion. Corrosion of Al alloys is a serious industrial problem that typically is remedied by using hexavalent chromium (Cr 6+ ) coatings. Cr 6+ coatings are a hazard for human health and the environment and due to new OSHA requirements these coatings have to be replaced. A possible alternative to Cr 6+ coatings is conjugated polymer (CP) coatings that have shown to provide a very good corrosion protection on Al. Our research group has been exploring various conjugated polymers (e.g., polyaniline, polypyrrole and polythiophene) for use as corrosion control coatings, particularly for aluminum alloys [1-6]. Depositing a CP on Al alloy is a challenge because of a simultaneous growth of oxide layer. We have used an approach based on electron transfer mediators (ETMs) [1, 2] to deposit CPs on a surface of Al. In a recent publication we reported the influence of ETMs on the deposition of the CP polypyrrole (PPy) on Al alloy surface and have shown that depending on the type of substitution on benzene ring (carboxyl or sulfonate) and its position, mediating properties of the compound dramatically vary [7]. In this paper we report a successful approach for depositing PPy onto artificially grown Al oxide in the presence of electron transfer mediators, such as Tiron. The rationale for depositing PPy on the oxide layer is to combine the barrier properties of Al oxide with corrosion inhibiting properties of PPy. The Al oxide is a dielectric and in order to deposit CP onto oxide of a few microns thickness, it has to be porous. In this paper Al oxide was obtained electrochemically by a method that is usually used to obtain anodic porous alumina (APA), such as described in [8]. However, due to variations in the composition of the alloy 1 , in our experiment the oxide was not comprised of regular distributed pores like in APA, but contained small pores of different size randomly distributed over the entire surface of the sample. Porous