Jean-Christophe Lacroix

Electrosynthesis of adherent polyaniline films on iron and mild steel in aqueous oxalic acid medium

Abstract Polyaniline (PANi) films can be electrosynthesized by oxidation of aniline on iron and mild steel in a one-step process from an aqueous oxalic acid medium which passivates substrates. Homogeneous and strongly adherent films of controlled thickness can be deposited either in the potentiodynamic or galvanostatic modes. These films are characterized by IR, X-ray photoelectron spectroscopy (XPS), gel permeation chromatography (GPC) and matrix-assisted UV-laser desorption ionization (MALDI) techniques, and have a structure similar to that of PANi deposited on platinum. Iron samples coated with PANi exhibit much better protection against corrosion in an acidic solution (0.4 M NaCl + 0.1 MHCl) than the polypyrrole-coated ones. Attempts to grow PANi films on zinc or zinc—nickel alloy in oxalic acid were unsuccessful because the formation of insulating layers prevents electropolymerization.

Electrolyte Effects on the Switching Reaction of Polyaniline

This report describes the electrochemical behavior of polyaniline prepared in aqueous solution with various acid electrolytes. Electroactive polyaniline with two different cyclic voltammograms, i.e., with and without the additional peak at 500 mV, can be produced by controlling the current densities during the preparation. The oxidation reaction is coulombically reversible, and the rate depends on the acidity of the solution but is independent of the nature of the counter anion. In solutions more acidic than 0.1M, the charge is linear with time in the initial period. In 10−3 M acid solutions, the charge has a dependence. The films are also electroactive in nonaqueous solvents, and voltammograms with well‐defined waves result when the solution contains both organic salt and protic acid electrolyte. Polyaniline is stable in the dry state but not in aqueous electrolyte. TGA shows that the material dehydrates at 80°C and completely decomposes at 185°C. SEM analyses show that the initially deposited film is a continuous film and that the subsequent deposit has a fibril structure.

Electrodeposition of protective polyaniline films on mild steel

Abstract The electrodeposition of protective polyaniline (PANi) films on mild steel from aqueous oxalic acid is reported. The electropolymerization of aniline occurs on a surface passivated by the precipitation of an Fe(II)-oxalate layer and leads to strongly adherent films with a controlled thickness and with the same structure as the idealized emeraldine base. When they are dipped in an acidic solution (0.4 M NaCl + 0.1 M HCl) the PANi-coated iron samples exhibit very good protection against corrosion and are much more effective than polypyrrole coated ones.

Ultra-fast electropolymerization of pyrrole in aqueous media on oxidizable metals in a one-step process

Abstract A general one-step electrosynthesis process for polypyrrole (Ppy) films applicable to a large range of oxidizable metals is described. The process is based on the use of an aqueous medium containing a salicylate salt and pyrrole. The salicylate salt is quite specific: it passivates the substrate without preventing electropolymerization of pyrrole and, therefore, makes it possible to obtain strongly adherent PPy films, with controlled thickness, either by cyclic voltammetry or by electrolysis at constant current. In the latter case the process does not involve any induction period corresponding to a preliminary dissolution of the metal, the current efficiencies are close to 100%, and the deposition rate can be very high (1 μm s −1 , corresponding to current densities as high as 500 mA cm −2 ).

Characterization of polyaniline films electrodeposited on mild steel in aqueous p-toluenesulfonic acid solution

Aqueous p-toluenesulfonic acid solution is used to electrosynthesize a polyaniline (PANi) film on mild steel. Polarization of the substrate in this medium leads to passivation of the surface mainly via the formation of an iron oxide layer. When aniline is added to the solution, electropolymerization is not hindered and a dark green deposit is obtained in high yield (80%). Spectrochemical techniques (IR, XPS and UV) and mass determination (SEC and MALDI) indicate that it has the same properties as reported for PANi. Evaluation of the anticorrosion performances of the film shows that the corrosion current is divided nearly by ten, suggesting that this polymer coating could be used for corrosion protection.

Application of sodium dodecylsulfate (SDS) micellar solution as an organized medium for electropolymerization of thiophene derivatives in water

Abstract Electropolymerization of bithiophene and 3,4-ethylene dioxythiophene has been performed in aqueous SDS solutions on Pt electrode. It has been shown that SDS increases the solubility of both monomers and lowers their oxidation potential. PBT and PEDOT films electrosynthesized in this medium present well-defined structures.

Aniline electropolymerization on platinum and mild steel from neutral aqueous media

Aniline has been electropolymerized on platinum from neutral aqueous electrolytes. The properties of the resulting polyaniline (PANI) films are similar to those obtained in acidic media. PANI films can be generated using multiple cyclic voltammetry or galvanostatically. In the former case, the molecular structure of the films depends on the inversion potential and two types of material can be generated. When potential sweeps are restricted to an inversion potential of 0.8 V, the films do not have a PANI-like structure, whereas an inversion potential of 1 V allows the deposition of short PANI-like chains, as demonstrated by SEC and MALDI-MS techniques. In the galvanostatic mode, the molecular structure of the films depends on the applied current density. There is a current density window which makes it possible to grow PANI films from neutral electrolytes with the same efficiency as in acids and which depends drastically on the experimental conditions. In the case of a 2 M LiClO4+0.4 M aniline solution, a very high current density can be used for PANI deposition on platinum. These neutral aqueous electrolytes have been used for the deposition of PANI films on mild steel. The films are generated with less metal dissolution than when acid electrolytes are used and exhibit similar anticorrosion properties.

Anodic oxidation of 5-amino-1,4-naphthoquinone (ANQ) and synthesis of a conducting polymer (PANQ)

The electrooxidation of 5-amino-1,4-naphthoquinone (ANQ) at glassy carbon and Pt electrodes in acetonitrile leads to functionalized polymer films. Results from different spectroscopic techniques (FT-IR, UV-Vis, X-ray photoelectron spectroscopy (XPS)) and frontier orbital considerations converge to a definition of poly(5-amino-1,4-naphthoquinone) (PANQ) structure which is of the polyaniline-type bearing one quinone group per ANQ moiety.

Electroactive poly(aromatic amine) films for iron protection in sulfate medium

Polyaniline (PANil and poly(1,5-diaminonaphthalene) (PDAN) films can be deposited on iron from aqueous sulfuric acid. The films exhibit electroactive properties similar to those of PANi and PDAN generated on platinum. Electrosynthesis performed in the presence of both monomers leads to a composite film which presents excellent adhesion properties on iron. The composite film imparts a form of anodic protection for at least 9 days in pH 4 sulfate medium.

Electrochemical and spectroscopic properties of poly(3-methoxythiophene) electrosynthesized in an aqueous micellar medium

Abstract The electrosynthesis of poly(3-methoxythiophene) (PMOT) was performed on a Pt electrode in an aqueous micellar medium, containing sodium dodecylsulfate (SDS) as surfactant. The resulting PMOT film is electroactive and soluble in several organic solvents. It exhibits electrochemical and IR spectral properties typical of polythiophenes. Mass spectrometry (matrix assisted laser desorption ionization-time of flight or MALDI-TOF) shows that the film is mainly constituted of hexamers. The PMOT UV-Vis absorption and fluorescence spectra reveal remarkably distinct features relative to the monomer.