Quantitative depth profile study of polyaniline films by photothermal spectroscopies

Albuquerque, José Eduardo de; Balogh, D. T.; Faria, Roberto Mendonça

doi:10.1007/s00339-006-3789-4

Cited by 10 publications

(6 citation statements)

References 23 publications

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“…The gas acts as a piston in order to produce a sound wave which is detected by a microphone connected to the chamber. [6][7][8][9][10] As the microphone signal is proportional to radiation absorption by the sample, PAS gives results similar to absorbance spectra, i.e., conventional optical absorption spectroscopy. Also, as the signal depends on the modulation of the radiation source, PAS is able to perform a depth profile of the absorption in the sample, that is, at high modulation frequencies absorption information about the sample near the surface is obtained, while at low modulation frequencies the data come from deeper within the sample.…”

Section: Introductionmentioning

confidence: 94%

“…5 The heat propagation across the whole chamber is governed by heat diffusion equations of each medium coupled via boundary conditions at the interfaces (T a = T b and k a dT a /dx = k b dT b /dx, a and b are adjacent media, T is temperature and k is thermal conductivity). After all mathematical treatment, the normalized photoacoustic signal (S n ) produced by the microphone is: [5][6][7][8][9][10]17 (2) where r s = b s /s s , b s is the sample optical absorption coefficient, s s = (1 + i)a s with i = (-1) ½ and a s = (p f /a s ) ½ , a s is the sample thermal diffusivity, b nm = k n a n /k m a m (n = g, s, b, that is, g = gas, s = sample, b = backing), and L S is the sample thickness. This equation is a complex mathematical function of the optical, thermal and geometrical parameters of the system, and it governs our results for all the chopper frequencies.…”

Section: Photoacoustic Spectroscopy Theorymentioning

confidence: 99%

“…Also, as the signal depends on the modulation of the radiation source, PAS is able to perform a depth profile of the absorption in the sample, that is, at high modulation frequencies absorption information about the sample near the surface is obtained, while at low modulation frequencies the data come from deeper within the sample. 8,10 Vegetable oil is a valuable and versatile compound used as stabilizer, additive or raw material in the foodstuffs production. Its composition includes triacylglycerol (95 to 98%) and mixtures of minor compounds (2 to 5%) such as glycerides, free fatty acids, phospholipids, carotenoids, chlorophylls, sterols, tocopherols, proteins, resinous and mucilaginous materials and oxidative products.…”

Section: Introductionmentioning

confidence: 99%

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Photoacoustic spectroscopy as an approach to assess chemical modifications in edible oils

Albuquerque¹,

Santiago²,

Campos³

et al. 2013

J. Braz. Chem. Soc.

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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...

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Section: Introductionmentioning

confidence: 94%

Section: Photoacoustic Spectroscopy Theorymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Photoacoustic spectroscopy as an approach to assess chemical modifications in edible oils

Albuquerque¹,

Santiago²,

Campos³

et al. 2013

J. Braz. Chem. Soc.

View full text Add to dashboard Cite

show abstract

“…This technique typically uses a modulation of laser beam for inducing a thermal-wave (TW) field in the sample. The obtained TW distribution is then detected by various photothermal methods, such as photoacoustics [40], photothermal spectroscopy [41] or PPE techniques [11,42]. Recently, many useful applications of the photopyroelectric (PPE) effect have been reported with regard to the measurement of both thermal and optical absorption properties of a material [43].…”

Section: Theoretical Background: Photopyroelectric Techniquementioning

confidence: 99%

Measuring Nanofluid Thermal Diffusivity and Thermal Effusivity: The Reliability of the Photopyroelectric Technique

Noroozi¹,

Zakaria²

2017

Nanofluid Heat and Mass Transfer in Engineering Problems

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It is important to study nanofluids to understand their extraordinary thermal properties and how the size, concentration and agglomeration of the nanoparticles affect those properties. Photopyroelectric (PPE) technique has been well established in the use of non-destructive measurement of thermal diffusivity and thermal effusivity, by using polyvinylidene fluoride (PVDF) films as sensitive pyroelectric sensors in thermally thick conditions instead of using very thick ceramic sensors. There have been two proposed practical configurations for the PPE technique, the back and the front PPE configurations, to obtain both the thermal diffusivity and effusivity, which are suitable thermal parameters of materials. This PPE technique involves the measurement of thermal waves in the sample due to absorption of optical radiation, by placing a pyroelectric sensor in thermal contact with the sample. This chapter provides a review of the back and the front PPE configurations to determine the thermal diffusivity and effusivity of nanofluids, sample preparation techniques using high-amplitude ultrasonic dispersion and data analysis for metal oxide-based nanofluid materials.

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“…6,–9 Furthermore, PAS of condensed-phase samples is often applied to depth profiling of layered samples and two-and three-dimensional tomographic imaging for biomedical applications. 10,–12 Although there have been several reports discussing the use of tunable infrared sources, such as quantum cascade lasers (QCLs) and CO 2 lasers, to obtain photoacoustic spectra of gases, 13,–20 the application of these sources in photoacoustic experiments on condensed-phase samples are minimal. 9,21,22 In this current work, we report on the use of a continuously tunable pulsed QCL, in combination with a photoacoustic cell designed for solid and liquid samples, for detection of tetraethoxysilane (TEOS) or glycerol films deposited on a substrate, and discrimination between these compounds and the substrate itself based on sample depth profiling.…”

Section: Introductionmentioning

confidence: 99%

Quantum Cascade Laser Based Photoacoustic Spectroscopy for Depth Profiling Investigations of Condensed-Phase Materials

2012

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We report on the development of a photoacoustic device for the detection of condensed-phase materials. A mid-infrared quantum cascade laser (QCL) was used for depth-profiling studies to distinguish among glycerol films and tetraethoxysilane (TEOS) films deposited on photoresist-coated silicon wafers. The QCL was continuously tunable from 1015 cm−1 to 1240 cm−1, allowing for collection of photoacoustic vibrational spectra for these materials. Variation of the laser pulse repetition rate allowed for identification and molecular discrimination of glycerol, TEOS, and photoresist based solely on photoacoustic spectra collected at different film depths.

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Quantitative depth profile study of polyaniline films by photothermal spectroscopies

Cited by 10 publications

References 23 publications

Photoacoustic spectroscopy as an approach to assess chemical modifications in edible oils

Photoacoustic spectroscopy as an approach to assess chemical modifications in edible oils

Measuring Nanofluid Thermal Diffusivity and Thermal Effusivity: The Reliability of the Photopyroelectric Technique

Quantum Cascade Laser Based Photoacoustic Spectroscopy for Depth Profiling Investigations of Condensed-Phase Materials

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