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URI permanente desta comunidadehttps://locus.ufv.br/handle/123456789/11779
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Item Quantitative depth profile study of polyaniline films by photothermal spectroscopies(Applied Physics A, 2007-03) Albuquerque, J. E. de; Balogh, D. T.; Faria, R. M.In this study, we carried out a quantitative depth profile analysis of the optical properties of slightly and strongly doped polyaniline (PANI) films, using both photoacoustic and photopyroelectric spectroscopies. As the thermal diffusion length varies inversely to chopper modulation frequency, then at high chopping frequencies information about the sample near the surface is obtained, while at low chopping frequencies the data come from deeper within the sample. The objective of this study is to analyze how the polyaniline doping process in acidic media occurs in the polymeric chain using the photothermal techniques. The results showed that polymeric chains of the doped samples are composed of undoped regions, while polymeric chains of slightly doped samples present doped regions to a lesser degree. These conclusions are in accordance with published results in which doped PANI films exhibit a granular conductive regions in a quasi undoped matrix. In addition, the photothermal spectra showed that the doping process of PANI, in which films are dipped in hydrochloric acid solution, is more effective in the external surface of the films.Item Study of optical absorption differences of doped polyaniline films by photothermal spectroscopies(Applied Physics A, 2007-07-29) Albuquerque, J. E. de; Melo, W. L. B.; Faria, R. M.In this work, we studied the optical absorption spectral differences between doped and slightly doped polyaniline films and a derivative by photopyroelectric and photoacoustic spectroscopies. There exist great spectral differences between doped and slightly doped samples as shown by conventional optical absorption spectroscopy, but not greatly evidenced by photopyroelectric spectroscopy. The latter was applied to obtain thermal parameters such as thermal diffusivity and thermal conductivity, and as a result it showed that these thermal properties of polyaniline films are very similar for doped and slightly doped samples. Also it showed that for thicker films (about 20 μm), there are no significant optical absorption differences between them. However, for thin films both techniques showed greater optical absorption differences for doped and slightly doped samples, mainly detected by photoacoustic spectroscopy. These behaviors are in accordance with published results which is the granular metal model for polyaniline. This model explains the polyaniline polymeric matrix as formed by conductive islands in the insulating bulk material.