José E. Pereira da Silva

Polyaniline Based Acrylic Blends for Iron Corrosion Protection

Instituto de Qui´mica, Universidade de Sa˜o Paulo, 05513-970 Sa˜o Paulo, BrazilCoating strategies for corrosion protection considering intrinsically electronic conducting polymers have become important mainlybecause of restrictions on the use of heavy metals due to their environmental problems. This work presents the electrochemicalbehavior of an acrylic blend formed by sulfonate-doped polyaniline and poly~methyl methacrylate! used for corrosion protectionof iron in chloride solutions. The results would indicate that these blends have a dual protection mechanism; forming a passivatingcomplex with the dopant anion ~camphorsulfonate! and simultaneously acting as a physical barrier to avoid chloride anionpenetration.© 2001 The Electrochemical Society. @DOI: 10.1149/1.1381288# All rights reserved.Manuscript submitted October 28, 2000; revised manuscript received April 20, 2001. Available electronically June 15, 2001.

Mechanism of Action of Corrosion Protection Coating for AA2024-T3 Based on Poly(aniline)-Poly(methylmethacrylate) Blend

A corrosion protection coating for AA2024-T3 composed of a blend of camphorsulfonate-doped poly(aniline) (PANI) and poly(methylmethacrylate) (PMMA) is described. The open-circuit potential (OCP) for the bare and coated alloy in H 2 SO 4 solutions is presented vs. time. Raman spectroscopy revealed the oxidation state of the PANI component of the blend, both on undamaged films and as a function of distance away from a scratch on purposefully damaged films. The open-circuit and Raman data show galvanic coupling between the coating and the alloy, causing reduction of the PANI component. Scanning electrochemical microscopy was used to monitor H 2 evolution over a scratch on the surface of either PANI blend or PMMA films coated on AA2024. These experiments show that the scratched surface is highly active toward H 2 evolution when coated with only a PMMA film. In contrast, the blend coating drastically suppresses the amount of H 2 evolution in a scratch. This suppression of H 2 evolution was mimicked by poising the OCP of the PMMA-coated alloy at the same value at which it is poised by the PANI-containing film. It is shown that camphorsulfonate anion has no inhibitory effect on H 2 evolution in scratches on PMMA-coated AA2024.

Electrochemical and Raman studies on a hybrid organic–inorganic nanocomposite of vanadium oxide and a sulfonated polyaniline

The electrochemical and gravimetric behavior of a nanocomposite ([PSPAN]0.3V2O5·nH2O) comprised of poly(N-propane sulfonic acid aniline) (PSPAN) and vanadium pentoxide xerogel are described. Electrochemical quartz crystal microbalance (EQCM) measurements show that the charge compensation process in this nanocomposite occurs predominantly by Li+ transport with a small amount of accompanying solvent, especially at low scan rates. The diffusion coefficients for Li+ in both the vanadium pentoxide xerogel and in the nanocomposite are measured using the galvanostatic intermittent titration technique (GITT), and a value of 1×10−12 cm2 s−1 was determined for both materials. Combination of these results with electrochemical impedance spectroscopy (EIS) measurements shows that the nanocomposite is more electronic conductor and exhibits shorter ionic diffusion pathways than the vanadium pentoxide parent xerogel material. In situ Raman spectroscopic results on the nanocomposite unambiguously demonstrate the oxidation and reduction of the PSPAN component during redox cycling of the nanocomposite, even though the electrochemical signature of the PSPAN is obscured by that of the vanadium pentoxide component.

Redox Behavior of Crosslinked Polyaniline Films

The redox processes of secondarily doped and the pre-heated primarily doped polyaniline (150oC, 6-12 h) were investigated by in-situ resonance Raman spectroscopy. Raman spectra of secondarily doped polymer is more dependent on potential than those observed in the pre-heated primarily doped polymer. These different behaviors were attributed to the presence of different degree of crosslinking in the polymers. The presence of different amounts of crosslinking was confirmed by thermogravimetric analysis, UV-vis spectroscopy and cyclic voltammetry.

Spectroscopic Characterization of the Inclusion Compound Formed by Polyaniline and β-Cyclodextrin

The encapsulation of emeraldine base (EB) was achieved by the thread of several β-CD units onto the polymer chain. The formation of the inclusion compound was confirmed by X-ray powder diffraction, IR and Raman spectroscopies. It was shown that despite encapsulation EB is still prone to the doping effect of HCl or iodine vapours.

Characterization of conducting polyaniline blends by Resonance Raman Spectroscopy

Raman and optical microscopy were used to investigate possible interactions between polyaniline (PANI) and different insulating polymers in conducting blends. Resonance Raman and optical micrographs were used to study the physical interaction in materials. Analysis Raman spectra was done investigating the relative intensity of bands at 574 and 607 cm-1. A relationship between Raman bands and conductivity was also proposed.

Racemic synthesis of 1,2-secomicrominutinin

The racemic 1,2-secomicrominutinin (25) was synthesized employing the intramolecular cycloaddition reaction of an (alkenyloxy)ketene, prepared from the corresponding tosylate. The (alkenyloxy)ketene undergoes intramolecular [2+2] cycloaddition to give tricyclic benzocyclobutafuranone (16), which by Baeyer-Villiger oxidation gives a benzofuranofuranone (17). Reaction of the latter compound with methyl propiolate, catalyzed by triphenylphosphine, produced the cinnamic ester derivative (25).

Molecular Dynamics Simulations of Cetyltrimethylammonium Bromide (CTAB) Micelles and their Interactions with a Gold Surface in Aqueous Solution

Surfactants are molecular structures with remarkable physicochemical properties and applications. Most of their characteristics are due to their ability to promote aggregation and interactions with different interfaces. The scarcity of theoretical studies dedicated to evaluating the forces involved in these interactions prompted us to propose other models capable of reproducing the experimental data in better ways. We carried out molecular dynamics (MD) simulations to obtain a model for cetyltrimethylammonium bromide (CTAB), selected from gromos54a7 force field parameters, that better describes most of its behaviors in aqueous solution (micellar structure, counterion dissociation, etc.) and its adsorption pattern on a gold surface. The parameters adopted for one of the models were able to mimic several characteristics suggested by experimental measurements of the CTAB micelles, as well their adsorption pattern on a gold surface. Indeed, this model was able to obtain quasi-spherical micelles, as well as a pattern of adjacent cylindrical micelles with alkyl chain interactions on a gold surface.