Claudio H. B. Silva

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.

Spectroscopic Study on the Structural Differences of Thermally Induced Cross-Linking Segments in Emeraldine Salt and Base Forms of Polyaniline

This paper reports the spectroscopic study on the structural differences of thermally induced cross-linking segments in polyaniline in its emeraldine salt (PANI-ES) and base (PANI-EB) forms. Casting films of PANI-ES (ES-film) and PANI-EB (EB-film) were prepared and heated at 150 °C under atmospheric air for 30 min. Raman spectra excited at 632.8 nm of heated ES-film presented the characteristic bands of phenazine-like structures at 1638, 1392, and 575 cm(-1), whereas EB-film showed lower relative intensities for these bands. The lower content of phenazine-like segments in heated EB-film is related to residual polaronic segments from preparation procedures, as revealed by Raman. This statement was confirmed by a sequence of thermal and doping experiments in both films. Quantum-chemical calculations by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) showed that the phenazine-like structure presents the intense Raman band at 1350 cm(-1) due to heterocycle breathing mode, and the non-phenazine-like structure (substituted hydrophenazine-type) presents higher energy for HOMO-LUMO transition, indicating the lack of conjugation in the heterocycle compared with the phenazine-like structure. According to experimental and theoretical data reported here, it is proposed that only thermally treated PANI-ES presents phenazine-like rings, whereas PANI-EB presents heterocyclic non-aromatic structures.

Hybrid materials of polyaniline and acidic hexaniobate nanoscrolls: high polaron formation and improved thermal properties

The study of hybrid materials of components combined in the nanoscale range is an active field due to the possibility of new technologically relevant applications. This paper reports the structural characterization and investigation of the thermal properties of a new hybrid material formed by the mixture of dispersions of polyaniline (PANI), a conducting polymer, and acidic hexaniobate nanoscrolls (NbONsc), a semiconducting metal oxide. Resonance Raman spectra indicate that the relative population of polaronic to bipolaronic segments in the hybrid material prepared at pH 2.5, is higher than indicated for pristine PANI prepared in 1.0 mol L−1 hydrochloric acid. Although the hybrid material was prepared at pH 2.5, electron paramagnetic resonance spectra indicate similar polaron populations compared with pristine PANI, which indicate that the hybrid material presents high conversion of bipolaronic to polaronic segments. Such features were attributed to a strong interaction between the PANI and the acidic NbONsc, inducing conformational changes of the polymeric chains and high formation of polarons at pH 2.5 (secondary doping). Thermogravimetric analyses showed that the onset temperatures of polymer decomposition in the hybrid materials are ca. 15 °C higher compared with pristine PANI. More interestingly, RR spectroscopy data showed that PANI in the presence of NbONsc remains in its doped form even after heating at 150 °C for 90 min, which was not observed for the pristine polymer. Based on a simple experimental procedure reported here, thermally stable hybrid nanomaterials of highly doped PANI and acidic hexaniobate nanoscrolls were successfully prepared and characterized and exhibit potential applications for electronic devices.

Electrochemical template synthesis of adherent polyaniline thin films with tubular structure

The synthesis of nano and microstructured thin polyaniline (PANI) films by a simple and very efficient template-assisted method is presented. This work shows the synthesis and characterization of acoustically rigid thin films structured at nanotubular shape by using methyl orange (MO) as a template-assisted system. The amount of the tubes can be easily controlled by the charge passed. The morphology for different films growth was characterized by field emission scanning electron microscopy (FESEM), Atomic force microscopy (AFM), and quartz crystal microbalance with dissipation mode (QCM-D). Raman spectroscopy results show important changes in the conformational PANI chain of the tubular material compare with a non-tubular one that provokes the increase of bipolarons population. This should be responsible by some changes in the electrochemical behavior of tubular film compared with the granular material, due to the higher conductivity when the emeraldine form starts to be formed.