S. Aeiyach

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.

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 ).

A new method for obtaining polyparaphenylene films by electrochemical oxidation of (Benzene-SbF5) π-complexes in SO2 medium

Abstract A new method for preparing polyparaphenylene films by electrochemical oxidation of benzene in SbF5SO2 medium is described. It is shown that formation of a π-complex between SbF5 and benzene lowers the benzene oxidation potential by about 0.8 V. The polymer chains, analysed by i.r. spectroscopy, show very good linearity and the degree of polymerization ranges from 15 to 30 for t = −75°C and t = −30°C, respectively. In contrast, no significant variations were observed in the u.v. spectra, which in all cases are characterized by an absorption band at about 3.5 eV. n-Doping of these films was carried out in (Bu)4NBF4-THF and was observed to be homogenous when the film was about 1 μm thick.

A. one-step electrosynthesis of PPy films on zinc substrates by anodic polymerization of pyrrole in aqueous solution

A one-step synthesis of adherent polypyrrole (PPy) films on zinc electrodes is achieved by electro-oxidation of pyrrole in aqueous oxalate solution containing small amounts of sulfide ion at pH 5 in either the galvanostatic or potentiodynamic modes. Very good electropolymerization coulombic efficiencies were obtained (γ=90%) for current densities ranging between 4 and 20 mA cm−2.

Electrochemical synthesis and redox behaviour of polypyrrole coatings on copper in salicylate aqueous solution

Abstract In this work, polypyrrole (PPy) coatings have been successfully electrodeposited on copper substrates from aqueous salicylate solutions. Homogenous and uniform films can be grown under galvanostatic or potentiostatic control without noticeable substrate dissolution. The redox behaviour obtained for the films is similar to that displayed by PPy grown under the same conditions on noble metals. Strong adherence to copper is observed as far as PPy is in its oxidised state but it is lost when the system is subjected to potentials lower than −0.5 V versus saturated calomel electrode (SCE).

Low potential electropolymerization of thiophene in aqueous perchloric acid

Abstract Electropolymerization of thiophene on Pt and indium tin oxide electrodes was investigated in moderately concentrated aqueous perchloric acid. The use of this medium increases the solubility of thiophene and lowers the oxidation potential of the monomer to about 0.9 V vs. SCE instead of 1.6 V found in acetonitrile. The polythiophene films synthesized by this technique are homogeneous and have properties very similar to films formed in organic media. In particular, Fourier transform IR analysis showed that strictly α,α′-polythiophene chains are obtained with a degree of polymerization of about 40 and conductivities ranging between 0.1 and 1 S cm −1 .

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.

Electropolymerization of thiophene on oxidizable metals in organic media

The electropolymerization of thiophene on oxidizable metals (Fe, Zn, Al) has been investigated in different organic media (acidic, neutral or basic) with a view to obtaining adherent and homogeneous polythiophene (PT) films. In propylene carbonate (PC), considered as a neutral medium (DN = 15) and a good solvent for the electropolymerization of thiophene on noble metals, it was found that, of several salts, PF6− alone could hinder the anodic dissolution of iron and allow the galvanostatic electropolymerization of thiophene on this metal. In a basic solvent, such as THF (DN = 20), electropolymerization of PT could not be achieved, due to passivation of the metal making the electrode surface highly insulating. The best results were obtained in dichloromethane (DCM), considered as acidic (DN = 4), which allowed the deposition of homogeneous PT films on Fe and Al in potentiodynamic or galvanostatic modes easily, and on Zn in the galvanostatic mode only. Polymer films obtained on these metals in PC and DCM were analysed by IR spectroscopy and XPS; their structure appeared quite similar to those obtained on Pt with, in particular, strictly α, α′ coupling of thiophene units. However, the conductivities of these PT films, related to their doping level, are much lower than on Pt (10 S cm−1), and seem to be correlated with the redox potential of the metal: 10−3 S cm−1 with Fe and Zn, 10−4 S cm−1 with Al. The adherence of PT films synthetized in DCM on Fe and Zn is not very good (maximum adherence about 35% for iron and 0% for Zn). In the case of iron it was found to decrease when the current density increased from 4 to 10 mA cm−2. With Al, the adherence is excellent (100%) and is due to the formation of SAl and CAl bonds, as confirmed by XPS analysis.

Electropolymerization of bithiophene on Pt and Fe electrodes in an aqueous sodium dodecylsulfate (SDS) micellar medium

A new method for preparing polythiophene films by electrochemical oxidation of bithiophene in an aqueous micellar medium on iron and platinum electrodes is described. It is shown that sodium dodecylsulfate (SDS) increases the solubility of bithiophene in water, lowers its oxidation potential and inhibits the dissolution of an iron electrode. Polybithiophene films prepared by this technique are very homogeneous and adherent to the electrode surface. X-ray photoelectron and IR spectroscopy indicates that both dodecylsulfate anion and perchlorate are involved in the polymer doping process. Raman analysis shows that the quantity of structural defects in the polymer chains decreases with decreasing film thickness. The morphology of the films imaged by scanning electronic and atomic force microscopy shows that disorder at the polymer surface increases with film thickness.