Ana Maria Rocco

Miscibility, crystallinity and morphological behavior of binary blends of poly(ethylene oxide) and poly(methyl vinyl ether–maleic acid)

DSC and optical microscopy were used to determine the miscibility and crystallinity of blends of poly(ethylene oxide) (PEO) with poly(methyl vinyl ether–co–maleic acid) (PMVE–MAc). Single Tg was observed for all blends, indicating miscibility. The dependence of Tg on the weight per cent of PEO presents a negative deviation from linearity at high PEO content, associated to a greater blend free volume, mobility and flexibility than in pure PEO. A progressive decrease in the degree of crystallinity and in the size of the PEO spherullites as the PMVE–MAc is added is observed. FTIR provided evidence of specific interaction between the polymers.

Tecnologia dos nanotubos de carbono: tendências e perspectivas de uma área multidisciplinar

An overview of the properties of carbon nanotubes is presented as a function of the structural characteristics and of the method of synthesis of these novel advanced materials. Emphasis is given to the catalytic decomposition of hydrocarbons over metal-supported catalysts and also the role of the support in obtaining homogeneous carbon nanotubes in high yelds is discussed. Some potential and real applications of carbon nanotubes are presented in a perspective view.

Blends of poly(ethylene oxide) and poly(4-vinylphenol-co-2-hydroxyethyl methacrylate): thermal analysis, morphological behaviour and specific interactions

DSC and optical microscopy were used to determine the miscibility and crystallinity of blends of poly(ethylene oxide) (PEO) with poly(4-vinylphenol-co-2-hydroxyethyl methacrylate) (PVPh-HEM). A single glass transition temperature was observed for all blends, indicating miscibility. A progressive decrease in the degree of crystallinity and in the size of the PEO spherullites is observed, as PVPh-HEM is added. FTIR was used to probe the intermolecular specific interactions of the blends and the miscibility of the blend is mainly attributed to PVPh-HEM/PEO intermolecular interactions via hydrogen bonding.

Synthesis and properties of bis(1,3-dithiole-2-thione-4,5-dithiolato)bismuthate(1-) salts, [Q][Bi(dmit)2]. Crystal structure of [AsPh4][Bi(dmit)2]·1/2DMSO: comparison of the solid state structures of [Q][Bi(dmit)2] and [Q][Sb(dmit)2]

Abstract Ionic complexes, [Q][Bi(dmit)2] (5:QNEt4, NBu4, 1,4-Me2-pyridinium and AsPh4), have been obtained from BiBr3 and [Q]2[Zn(dmit)2] [H2–dmit4,5-dimercapto-1,3-dithiole-2-thione]. As established by the crystal structure determination of [(5:QAsPh4)·1/2DMSO], the cations have near tetrahedral geometries and are well separated from the anions. The anions, containing chelating dmit ligands, are linked into chains via Bi–thiolato–S inter-anion bonds: Bi2S2 rings are formed within the chains, with Bi⋯Bi distances alternating between 3.7760(3) and 3.9092(3) A. The bismuth atoms are six-coordinate, arising from two inter-anion Bi–S [Bi–S=3.0391(13) and 3.1643(14) A] and four intra-anion Bi–S bonds [between 2.6680(13) and 2.8370(13) A], with stereochemistries, including the equatorial-sited stereochemically active lone pair, of distorted pentagonal bipyramids. There are no S⋯S contacts between the anions less than the sum of the van der Waals radii. Comparisons are made between the structure of [(5:QAsPh4)·1/2DMSO] and those reported previously for (5:QNEt4), [(5:QNEt4)·1/2Et2O] and [(5:QNBu4) as well as those for [Q][Sb(dmit)2] (4).

Specific interactions in blends of poly(ethylene oxide) and poly(bisphenol A-co-epichlorohydrin): FTIR and thermal study

Blends of poly(ethylene oxide) (PEO) of high molecular weight with poly(bisphenol A-co-epichlorohydrin) (PBE) with high epoxy equivalent were studied spectroscopically, thermally and morphologically. As similar systems of low molecular weight, a single Tg was observed for all blends, indicating miscibility. A progressive decrease in the degree of crystallinity and in the size of the PEO spherulites as the PBE is added is also observed. Quantitative analysis from FTIR spectra provided determination of specific interactions between the constituents and their variation with PEO content. Simulations were performed utilising the spectra of the pure polymers to confirm that the observed changes in the experimental spectra of the blends were due to interaction between the polymers. 2003 Elsevier Ltd. All rights reserved.

Study of the crystallization kinetics : Poly(ethylene oxide) and a blend of poly(ethylene oxide) and poly(bisphenol A-co-epichlorohydrin)

A kinetic study of the crystallization of poly(ethylene oxide) (PEO) and of a blend of PEO+poly(bisphenol A-co-epichlorohydrin) (PBE) was performed by using DSC in a non-isothermal program at constant cooling rates. The curves obtained were analyzed by the Kissinger, Ozawa and Friedman methods, with determination of the kinetic parameters in each case. As a consequence of the presence of PBE, the kinetic parameters were altered, leading to the conclusion that PBE has some influence on the crystallization of PEO, modifying its mechanism.

Evaluation of chromate passivation and chromate conversion coating on 55% Al–Zn coated steel

Abstract Steel sheets coated with hot-dip 55% Al–Zn is used in situations where better atmospheric corrosion resistance is needed. This type of alloy coating exhibits greater durability due to aluminum barrier protection together with zinc galvanic protection. The surface treatments for this alloy are based on chromate. Usually, two different cromating coatings are deposited on the alloy. The first is used to improve the corrosion resistance on it and the second to increase the adherence of paint films. The aim of the present work is to compare the corrosion resistance and electrochemical behavior of the 55% Al–Zn after the first and the second chromate conversion coatings treatment. Studies of cyclic voltammetry, atomic absorption and Auger spectroscopy showed that the second treatment used to increase the adherence of the paint, turns the surface more susceptible to corrosion.

Synthesis of Sr-doped LaMnO3 and LaCrO3 powders by combustion method: structural characterization and thermodynamic evaluation

Manganita de lantânio dopada com estroncio (LSM) e cromita (LSC) em po, bem como as correspondentes amostras nao dopadas, foram sintetizadas pelo metodo de combustao, usando dois diferentes combustiveis (ureia e glicina). A ignicao da mistura reacional com ureia leva mais tempo e a temperatura maxima e maior do que usando glicina, para as amostras dopadas. Os calculos teoricos de calor de reacao e temperatura de chama adiabatica indicam condicoes favoraveis a combustao. No entanto, a calcinacao e uma etapa essencial para uma boa cristalizacao da fase perovskita. Os padroes de difracao de raios X mostraram a formacao apenas da fase perovskita para as amostras sintetizadas com ureia. Os tamanhos de cristalitos estao na faixa de 19-25 nm, com valores menores quando a ureia e usada como combustivel. Analises de microscopia eletronica de varredura mostraram a presenca de aglomerados, formados por particulas finas de diferentes formas. A analise termogravimetrica revelou que a perda de peso e muito maior para as manganitas, com queima completa dos orgânicos em 850-900 oC.

Dessorção iônica e degradação de filmes de polipirrol dopado com dodecilsulfato induzidas por elétrons de alta energia

Electron stimulated ion desorption (ESID) and degradation studies of polypyrrole doped with dodecylsulfate (PPy/DS) deposited on FTO were performed using time-of-flight mass spectrometry (TOF-MS) for ion analysis. The results suggest a strong contribution from fragments of the dodecylsulfate hydrocarbon chain to the mass spectra. In the 650-1500 eV energy range the ion yield curves show maxima at about 600, 1200 and 1400 eV, which can be related to carbon, nitrogen and oxygen-containing fragments, respectively, and interpreted in terms of the Auger Stimulated Ion Desorption (ASID) mechanism. Degradation studies indicate rapid loss of heavier hydrocarbons and an increase of bulk and substrate fragments. Some degradation profiles suggest formation of new species.

Thermal decomposition kinetics of tetraalkylammonium and dimethylpyridinium salts of the complex anion bis(1,3-dithiole-2-thione-4,5-dithiolate) bismuthate (−1)

In the present work, thermal decomposition kinetics of tetraalkylammonium and 1,4-dimethylpyridinium salts of the complex anion bis(1,3-dithiole-2-thione-4,5-dithiolate) bismuthate ([Bi(dmit)2]−) are addressed. Kinetic parameters for the decomposition reactions were obtained utilizing the Ozawa and Coats–Redfern (CR) models. Entropy, enthalpy, and free energy of decomposition processes were calculated from the CR results, providing information on the thermodynamic characteristics of the processes. The most probable mechanisms of thermal decomposition were indicated for the studied systems, along with their kinetic and thermodynamic parameters.