Search

Spectroscopic methods are used to investigate the formation of low molecular mass intermediates during aniline (ANI) oxidation and polyaniline (PANI) degradation. Studying ANI anodic oxidation by in situFourier transform infrared spectroscopy (FTIRS) it is possible to obtain, for the first time, spectroscopic evidence for ANI dimers produced by head-to-tail (4-aminodiphenylamine, 4ADA) and tail-to-tail (benzidine, BZ) coupling of ANI cation radicals. The 4ADA dimer is adsorbed on the electrode surface during polymerization, as proved by cyclic voltammetry of thin PANI films and its infrared spectrum. This method also allows, with the help of computational simulations, to assign characteristic vibration frequencies for the different oxidation states of PANI. The presence of 4ADA retained inside thin polymer layers is established too. On the other hand, FTIRS demonstrates that the electrochemically promoted degradation of PANI renders p-benzoquinone as its main product. This compound, retained inside the film, is apparent in the cyclic voltammogram in the same potential region previously observed for 4ADA dimer. Therefore, applying in situFTIRS is possible to distinguish between different chemical species (4ADA or p-benzoquinone) which give rise to voltammetric peaks in the same potential region. Indophenol and CO2are also detected by FTIRS during ANI oxidation and polymer degradation. The formation of CO2during degradation is confirmed by differential electrochemical mass spectroscopy. To the best of our knowledge, this is the first evidence of the oxidation of a conducting polymer to CO2by electrochemical means. The relevance of the production of different intermediate species towards PANI fabrication and applications is discussed. [ABSTRACT FROM AUTHOR]

Spectroscopic methods are used to investigate the formation of low molecular mass intermediates during aniline (ANI) oxidation and polyaniline (PANI) degradation. Studying ANI anodic oxidation by in situFourier transform infrared spectroscopy (FTIRS) it is possible to obtain, for the first time, spectroscopic evidence for ANI dimers produced by head-to-tail (4-aminodiphenylamine, 4ADA) and tail-to-tail (benzidine, BZ) coupling of ANI cation radicals. The 4ADA dimer is adsorbed on the electrode surface during polymerization, as proved by cyclic voltammetry of thin PANI films and its infrared spectrum. This method also allows, with the help of computational simulations, to assign characteristic vibration frequencies for the different oxidation states of PANI. The presence of 4ADA retained inside thin polymer layers is established too. On the other hand, FTIRS demonstrates that the electrochemically promoted degradation of PANI renders p-benzoquinone as its main product. This compound, retained inside the film, is apparent in the cyclic voltammogram in the same potential region previously observed for 4ADA dimer. Therefore, applying in situFTIRS is possible to distinguish between different chemical species (4ADA or p-benzoquinone) which give rise to voltammetric peaks in the same potential region. Indophenol and CO2are also detected by FTIRS during ANI oxidation and polymer degradation. The formation of CO2during degradation is confirmed by differential electrochemical mass spectroscopy. To the best of our knowledge, this is the first evidence of the oxidation of a conducting polymer to CO2by electrochemical means. The relevance of the production of different intermediate species towards PANI fabrication and applications is discussed. [ABSTRACT FROM AUTHOR]

Two different approaches are used to produce conducting polymer nano-objects. One is a “top-down” approach which involves laser ablation of conducting polymer films using laser light interference patterns (direct laser interference patterning, DLIP) to produce various surface shapes, including nanowires and nanodots. Polyaniline(PANI) and polypyrrole (PPy) nanostructures could be easily produced by ablation of films, previously formed by in-situ polymerization of the aromatic monomers. The other is a “bottom-up” approach involving the controlled nucleation and growth during monomer polymerization. This is achieved by performing the polymerization at the interface of two immiscible solvents. Both kinds of nanomaterials are characterized using dynamic light scattering, TEM, EDAX, FTIR, UV-vis and fluorescence spectroscopy. The structures are studied by SEM-FIB, optical and fluorescence microscopy along with water contact angle. It is shown that nanometric sized structures can be made by both methods. The chemical structures are quite similar or identical to that of the bulk polymer. While PANI nanofibers are dispersed in acid media, due to the surface charge related with chain protonation, they agglomerate in neutral media. In the interest of biological applications, different soluble polymers are used to help disperse the nanofibers at neutral pH. Both the dispersing agent and PANI nanofibers have to be innocuous to biological cells and higher organisms, like frog larvae. The successful intake of PANI nanofibers into cancer line cells and frog larvae prompts its application as NIR radiation absorbers in photothermal or photoacoustic tumor therapy and/or tomography. [ABSTRACT FROM AUTHOR]