J.E. Pereira da Silva

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.

Electrodissolution of cobalt in carbonate/bicarbonate media

Abstract The electrodissolution of cobalt in carbonate/bicarbonate solutions was studied at room temperature by steady state polarisation, interfacial pH measurements and Raman spectroscopy. The active dissolution of cobalt leads to an initial CoO film formation. The metal passivation occurs by a slow transformation of the CoO into a Co 3 O 4 oxide. The influence of HCO 3 − and CO 3 2− anions was investigated. Two different parallel electrochemical processes were proposed to account for the anion role on the electrochemical steady state behaviour of cobalt in the studied solutions.

A comparative study of m-cresol treated polyaniline and Langmuir Blodgett films

Polyaniline films prepared by Langmuir-Blodgett technique were characterized by X- Ray diffractometry and Raman spectroscopy. The obtained results were compared with those from secondarily doped samples treated with HCSA and m-cresol. When LB films were doped with HCl vapour, the Raman spectrum obtained is different form that of PANI/HCl samples prepared by chemical or electrochemical polymerization, being very close to spectrum of PANI/CSA/m-cresol samples. In LB films a great increase in the intensity of the band correponding to free carriers indicates the important role played by the extended conformation and conductivity.

Polyaniline conformational studies in conductive blends using resonance Raman spectroscopy

Resonance Raman spectroscopy was used to characterize conductive blends of polyaniline (PANI) with poly(methyl methacrylate) (PMMA) and polyethylene (PE). Results obtained show that PANI treated with m-cresol or hexafluoro-2-propanol, maintains an extended conformation in the blends. In spite of the visual appearance of the materials prepared with PMMA or PE, Raman spectroscopy clearly shows the regions where the interaction between the components is strong.

Relation between structure and homogeneity of polyaniline blends by Infrared and Raman spectroscopies

Raman and Infrared spectroscopies were used to study physical and chemical interactions in polyaniline blends and to verify the degree of homogeneity in these materials. In more homogeneous blends, Raman spectra show an increase of the relative intensity of the band at 607 cm -1 linked with physical interaction. On the other hand, Infrared spectroscopy of polyaniline (PANI) blend with poly(methyl methacrylate) (PMMA) shows the shift to lower frequencies of the carbonyl band indicating chemical interaction.