Marcia L. A. Temperini

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.

Secondary doping of polyaniline studied by resonance Raman spectroscopy

Secondary doping of polyaniline (PANI) was explained by a change in the conformation of the polymeric chains from a coil-like to an extended structure, leading to an increase in the conductivity and in the crystallinity of polyaniline doped with functionalized organic acids. In this work, resonance Raman spectroscopy is used to characterize the secondary doping process aiming to understand the transformations in the different types of charged segments. Raman results give complementary data about the secondary doping process showing that together with the structural change of the polymeric chains there is also a chemical transformation of quinoid segments into semiquinone units. This fact was put in evidence by the careful analysis of Raman spectra at different excitation lines where different vibrational modes of chromophore groups are enhanced. This phenomena was also characterized by electron spin resonance (ESR) measurements that evidences an increase in the number of spins of PANI/CSA samples after the secondary doping process. Experimental results obtained by both techniques, resonance Raman spectroscopy and ESR, indicate the transformation of diamagnetic quinoid segments into radical cation semiquinone units.

Raman characterization of polyaniline induced conformational changes

Abstract Conformational changes induced by temperature and secondary doping process, were followed by Raman resonance spectroscopy and ESR measurements. Raman results give complementary data about the secondary doping process showing that together with the structural change of the polymeric chains, there is also a chemical transformation of quinoid segments into scmiquinoid units. When the temperature is raised, changes in Raman spectra arc coincident with those observed in secondarily doped samples, showing in this way, the importance of polymer conformation in the conductive behaviour. ESR measurements confirm the increasing amount of free radicals when the PANI/CSA films are treated with m-cresol in good agreement with Raman results.

Chemical analysis of polycyclic aromatic hydrocarbons by surface-enhanced Raman spectroscopy.

The use of surface-enhanced Raman spectroscopy (SERS) for trace determination of polycyclic aromatic hydrocarbons (PAHs) is described. This paper focuses on the development of SERS-active substrates that are specific for the characterization and spectroscopic study of PAHs. The SERS-active substrates are based on thin gold films evaporated on a glass surface previously treated with a mercaptoalkylsilane. SERS of PAHs was investigated over uncoated gold island films and over such films coated with a self-assembled monolayer (SAM) of 1-propanethiol. Adsorption of PAHs on a plain SERS-active Au-film led to a surface-induced decomposition of PAHs, due to catalytic properties of nanostructured gold. Thus, the functionalization of the SERS-active substrates by means of SAM was done aiming at a specific chemical interaction toward PAHs. Thus, in addition to preventing decomposition of the PAHs, the coating also concentrates the hydrophobic PAHs close enough to the SERS-active interface. Results show that high sensitivity, SERS-active nanostructured gold substrates that show selectivity towards PAHs were obtained, with the following properties: strong intensification of the Raman signal, reproducibility, and stability over time. The employed methodology enables the observation of excellent Raman spectra of PAHs in aqueous environment at ppm levels.

High performance gold nanorods and silver nanocubes in surface-enhanced Raman spectroscopy of pesticides.

The behavior of Au nanorods and Ag nanocubes as analytical sensors was evaluated for three different classes of herbicides. The use of such anisotropic nanoparticles in surface-enhanced Raman scattering (SERS) experiments allows the one to obtain the spectrum of crystal violet dye in the single molecule regime, as well as the pesticides dichlorophenoxyacetic acid (2,4-D), trichlorfon and ametryn. Such metallic substrates show high SERS performance at low analyte concentrations making them adequate for use as analytical sensors. Density functional theory (DFT) calculations of the geometries and vibrational wavenumbers of the adsorbates in the presence of silver or gold atoms were used to elucidate the nature of adsorbate-nanostructure bonding in each case and support the enhancement patterns observed in each SERS spectrum.

The role of cross-linking structures to the formation of one-dimensional nano-organized polyaniline and their Raman fingerprint.

In the present work, the resonance Raman, UV-vis-NIR and scanning electron microscopic (SEM) data of nanorods (about approximately 300 nm in diameter) and nanofibers (about approximately 93 nm in diameter) of PANI are presented and compared. The PANI samples were synthesized in aqueous media with dodecybenzenesulfonic acid (DBSA) and beta-naphtalenesulfonic acid (beta-NSA) as dopants, respectively. The presence of bands at 578, 1400 and 1, 632 cm(-1) in the Raman spectra of PANI-NSA and PANI-DBSA shows that the formation of cross-linking structures is a general feature of the PANI chains prepared in micellar media. It is proposed that these structures are responsible for the one-dimensional PANI morphology formation. In addition, the Raman band at 609 cm(-1) of PANI fibers is correlated with the extended PANI chain conformation.

Spatiotemporal distribution of different extracellular polymeric substances and filamentation mediate Xylella fastidiosa adhesion and biofilm formation

Microorganism pathogenicity strongly relies on the generation of multicellular assemblies, called biofilms. Understanding their organization can unveil vulnerabilities leading to potential treatments; spatially and temporally-resolved comprehensive experimental characterization can provide new details of biofilm formation, and possibly new targets for disease control. Here, biofilm formation of economically important phytopathogen Xylella fastidiosa was analyzed at single-cell resolution using nanometer-resolution spectro-microscopy techniques, addressing the role of different types of extracellular polymeric substances (EPS) at each stage of the entire bacterial life cycle. Single cell adhesion is caused by unspecific electrostatic interactions through proteins at the cell polar region, where EPS accumulation is required for more firmly-attached, irreversibly adhered cells. Subsequently, bacteria form clusters, which are embedded in secreted loosely-bound EPS, and bridged by up to ten-fold elongated cells that form the biofilm framework. During biofilm maturation, soluble EPS forms a filamentous matrix that facilitates cell adhesion and provides mechanical support, while the biofilm keeps anchored by few cells. This floating architecture maximizes nutrient distribution while allowing detachment upon larger shear stresses; it thus complies with biological requirements of the bacteria life cycle. Using new approaches, our findings provide insights regarding different aspects of the adhesion process of X. fastidiosa and biofilm formation.

The adsorption of 2‚ 2’: 6’‚ 2’’-terpyridine‚ 4’-(5-mercaptopentyl)-2‚ 2’: 6’‚ 2’’-terpyridinyl‚ and perchlorate on silver and copper surfaces monitored by SERS

Abstract The adsorption of 2,2′:6′,2″-terpyridine on Ag and Cu electrode surfaces has been studied by using surface enhanced Raman spectroscopy (SERS). Two types of surface complexes have been found on a silver electrode: the first one is stable near the open circuit potential, having bonding between tpy and silver active site analogous to the AgN bonding in the [AgI(tpy)Cl]·2H2O complex; and the second one is stable in the −0.1 to −0.5 V (Ag/AgCl) potential range, where the interaction between tpy and silver active site is similar to the CuN bonding in the [CuII(tpy)Cl2] complex. The SERS spectra of 4′-(5-mercaptopentyl)-2,2′:6′,2″-terpyridinyl (tpy–SH) have shown an increase in the relative intensity of the mercaptopentyl moiety bands and a band at 310 cm−1, assigned to the AgS stretching, indicating an adsorption through the S atom. In addition, using the Raman results of different copper perchlorate salts obtained with different hydration degrees, it has been possible to characterize the adsorption of perchlorate anion on silver electrode and the kind of coordination in the [CuII(tpy)(H2O)(ClO4)]ClO4 and [CuII(tpy)(H2O)(ClO4)2] complexes.

Spectroscopic Characterization of Oligoaniline Microspheres Obtained by an Aniline-Persulfate Approach

This paper investigates the structure of the products obtained from the polymerization of aniline with ammonium persulfate in a citrate/phosphate buffer solution at pH 3 by resonance Raman, NMR, FTIR, and UV-vis-NIR spectroscopies. All the spectroscopic data showed that the major product presented segments that were formed by a 1,4-Michael reaction between aniline and p-benzoquinone monoimine, ruling out the formation of polyazane structure that has been recently proposed. The characterization of samples obtained at different stages of the reaction indicated that, as the reaction progressed, phenazine units were formed and 1,4-Michael-type adducts were hydrolyzed/oxidized to yield benzoquinone. Raman mapping data suggested that phenazine-like segments could be related to the formation of the microspheres morphology.

2-Formylpyridinethiosemicarbazone and methyl derivatives: spectroscopic studies

Abstract The Z – E isomerization of 2 - formylpyridinethiosemicarbazone (PATS2), 2 - formylpyridine-2′-methyl thiosemicarbazone (2′MePATS2), 2 - formylpyridine-4′-methyl thiosemicarbazone (4′MePATS2) and 2 - formylpyridine-4′,4′-dimethyl thiosemicarbazone (4′,4′DMePATS2) was studied in various solvents by Raman and 1 H NMR spectroscopies. The interactions of alkali and alkaline earth perchlorates with these compounds were investigated in acetonitrile (ACN) solution. The results showed that the most favorable configuration in the solid state is E for PATS2, changing to Z configuration when methyl groups substitute the two hydrogen atoms of the N(4′) atom in 4′,4′DMePATS2. In solution, the E – Z equilibrium ratio depends on the compound and it is strongly affected by the solvent employed (H 2 O, DMSO, ACN and CH 2 Cl 2 ). These results are rationalized considering the possibility of intra and intermolecular hydrogen bonding and the donor number of the solvents. The interaction of alkali and alkaline earth perchlorates with these compounds in ACN solutions results in the formation of complexes with E -4′,4′DMePATS2 while for PATS2 these cations increase the rate of E – Z isomerization.