ÁREA: Materiais
TÍTULO: DMA, FTIR, Raman and UV-vís characterization of self
assembled films of PAni
AUTORES: Jesus Santana, A. (UFPI) ; Junior, I. (UFPI) ; Filho, J. (UFPI) ; Alberto Hidalgo, A. (UFPI)
RESUMO: Despite over 30 years in research, PAni is still one of the most popular polymers in organic electronics community. Easy to synthesize and simple doping control, can reach very high levels of conductivity, as 400 S/cm. In this work we use different techniques, such as DMA, FTIR, Raman, UV-vis and impedance to characterize PAni films, mainly to characterize miscibility. PAni is synthesized as described in reference [1], after synthesized, PAni powder
is dissolved in N-metyl pirrolidone (NMP), 0,05 g/L and self assembled films are obtained by casting the solution on glass slides after allowing solvent evaporation. PAni/PVC blends are obtained by similar methods but previous to the casting process both solutions with identical concentrations are mixed in the desired proportion.
PALAVRAS CHAVES: PAni; PAni/PVC blend; conformational change
INTRODUÇÃO: Polyaniline has received great attention in recent years for its chemical stability under ambient conditions, processability, ease of polymerization and doping,can reach very high levels of conductivity, as 400 S/cm, low cost and its unique properties. These advantages enable several technological applications that have been developed including industrially. Many works address the problem of conformational changes of PAni related with electrical properties, however, this conformational change is difficult to establish.The polyaniline is a linear polymer formed of aniline, which can exist in a number of oxidation states, their rings may exist in forms benzenoids as quinóides.The use of polyaniline (PANI) is of special importance due to its excellent thermal and chemical stability.The work focuses mainly on the synthesis of PANI and its characterization by spectroscopic techniques and dynamic mechanical analysis. Specifically of interest is also focus on the work electronic and chemical properties of the polymer.
MATERIAL E MÉTODOS: In this work we use different techniques, such as DMA, FTIR, Raman, UV-vis and impedance to characterize PAni films, mainly to characterize miscibility. PAni is synthesized as described in reference [1], after synthesized, PAni powder is dissolved in N-metyl pirrolidone (NMP), 0,05 g/L and self assembled films are obtained by casting the solution on glass slides after allowing solvent evaporation. PAni/PVC blends are obtained by similar methods but previous to the casting process both solutions with identical concentrations are mixed in the desired proportion.
RESULTADOS E DISCUSSÃO: The characteristic absorption bands are observed in the UV-vis-NIR reflectance spectroscopy. Powder samples show a clear shift of the polaronic band relative to self assembled films, probably associated to conformational changes during dilution and confirmed with Raman spectroscopy [2]. This change of the
polaronic band is also correlated to electrical properties, conductivity is higher on solvent processed samples where the polaronic band is red shifted ~20nm. Temperature behavior of conductivity (50 K to 400K), show the typical shape of semiconductors, with at least three different tangents indicative of at least two phase transitions that are related with mechanical properties determined by DMA. The high phase transition, at ~400K, is characterized by
change of the complex elastic modulus and mechanical loss factor (tan ) compatible with vitreous transition. However, doping sample with 0.1M conductivity increase until 300 K, where starts decreasing up to 400 K and then increase again. The decrease of conductivity between 300 K and 400 K is more typical of isolating samples and is still under study.
CONCLUSÕES: Impedance shows the shape of Josncher´s low with ~ n at high frequencies, indicating hoping transport. Arrhenius analysis to determine the energy barrier for hoping is under development.
AGRADECIMENTOS: FAPEPI, CNPq, CAPES, FINEP, UFPI.
REFERÊNCIAS BIBLIOGRÁFICA: [1] L. H. C. Matoso, Química Nova, 9, (1996)
[2] J. E. Pereira da Silva, S. I. Córdoba de Torresi, M. L. A. Temperini, Electochim. Acta (in
press)
[3] VALEUR, B. Molecular Fluorescence: Principles and Applications, 2001.
