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Photopyroelectric (PPE) spectroscopy, in the 350-1,075 nm wavelength range, was used to study the optical properties of electropolymerized melanin films on indium tin oxide (ITO) coated glass. The PPE intensity signal as a function of the wavelength lambda, V (n)(lambda) and its phase F (n)(lambda) were independently measured. Using the PPE signal intensity and the thermal and optical properties of the pyroelectric detector, we were able to calculate the optical absorption coefficient beta of melanin in the solid-state. We believe this to be the first such measurement of its kind on this material. Additionally, we found an optical gap in these melanin films at 1.70 eV.

ReceivedPhotopyroelectric spectroscopy (PPE) was used to study the thermal and optical properties of electropolymerized melanins. The photopyroelectric intensity signal and its phase were independently measured as a function of wavelength, as well as a function of chopping frequency for a given wavelength in the saturation part of the PPE spectrum. Equations for both the intensity and the phase of the PPE signal were used to fit the experimental results. From the fittings we obtained for the first time, with great accuracy, the thermal diffusivity coefficient, the thermal conductivity and the specific heat of the samples, as well as a value for the condensed phase optical gap, which we found to be 1.70 eV.

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Photothermal spectroscopies, photopyroelectric and photoacoustic, were used to obtain physical parameters of polyaniline–emeraldine base (PANI-EB) and poly(o-methoxyaniline)–emeraldine base (POMA-EB), such as thermic parameters like thermal diffusivity, thermal conductivity, and specific heat. These studies were done for PANI-EB and POMA-EB films in the 400<λ<900 nm wavelength range. The photopyroelectric intensity Vn(f ) and the phase Fn(f ) (f being the chopping frequency) for a given λ of the saturation part of the PPES spectrum signal were independently measured, as well as the intensity Vn(λ) and its phase Fn(λ). Equations of both the intensity and the phase of the PPES signal, taking into account the thermal and the optical characteristics of the PANI and POMA films and the pyroelectric detector, were used to fit the experimental results. It was observed that, in contrast with the strong doping dependence of the electrical conductivity, the thermal parameters of PANI films remained practically unchanged under doping. This apparent discrepancy is explained by the granular metal model of doped PANI.

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Espectroscopia fotoacústica foi utilizada tanto para obter algumas propriedades ópticas de óleos de soja, canola e oliva quanto para avaliar as alterações ocorridas devido ao tratamento térmico dos óleos. A intensidade do sinal fotoacústico normalizado e a sua fase foram medidas, independentemente, como uma função do comprimento de onda da fonte de radiação. Amostras de óleo foram aquecidas por 30 min após atingido o ponto de fumaça visando sua degradação. Depois disso, as amostras de óleo foram resfriadas e medições fotoacústicas foram conduzidas de forma a obter os espectros de absorção de amostras em ambas as condições degradadas e não degradada. A comparação entre as duas condições indicou que as amostras de óleo degradado exibiram alargamento das bandas de absorção na região ultravioleta do espectro, em relação à respectiva amostra com óleo não-degradado. Os picos das referidas bandas de absorção apresentaram um desvio para a região do vermelho.Photoacoustic spectroscopy was used to obtain optical properties of edible soybean, canola and olive oils as well to evaluate the oil modifications induced by thermal treatment. The normalized photoacoustic signal intensity and its phase were independently measured as a function of wavelength of the radiation source. The oil samples were heated up to the smoke point and then for additional 30 min in order to degrade them. After, the oil samples were cooled down and photoacoustic measurements were conducted in order to obtain the absorption spectra of samples at both degraded and non-degraded conditions. Comparisons between the two conditions indicate that the degraded oil samples exhibited widening of the absorption bands in ultraviolet region of the spectra, relative to the respective non-degraded sample. Also, the peaks of those absorption bands presented a red shift.Keywords: thermal degradation, fatty acid, food process, physicochemical properties, vegetable oil IntroductionThe photoacoustic spectroscopy (PAS) is a useful photothermal technique to obtain thermal and optical parameters of materials based on heat transfer due to absorption of radiation by the matter. 1 Many applications of this technique is found in the scientific literature, such as adulteration studies in powdered coffee, 2 kinetic study of Maillard reactions in milk powder, 3 and measurements of thermophysical properties of poly(3HB) and poly(3HB-co-3HV) polymers. 4 PAS is based on the photoacoustic effect discovered by Alexander Graham Bell in 1880. 5 This effect is obtained in a closed chamber which is filled with a gas (in general, air) and contains a transparent window which permits a modulated (chopped) radiation to reach the sample. If the sample absorbs this modulated radiation then heat is produced due to non-radiative de-excitation processes within it. Then the heat is transferred to the gas as according to the frequency of the radiation modulation. The gas acts as Photoacoustic Spectroscopy as an Approach to Assess Chemical Modifications in Edible Oils J. Braz. Chem. Soc. 370 a pis...