Photoacoustic and related photothermal techniques

Vargas, H.; Miranda, L. C. M.

doi:10.1016/0370-1573(88)90100-7

Cited by 412 publications

(185 citation statements)

References 231 publications

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“…10 In the crystalline phase, it can be observed from the d-spacing measurements by X diffraction that, up to 29 mol % of the HV content sequence, the HV units are accommodated in the PHB crystal lattice (isomorphism) by small lateral expansion of the unit cell but the crystal packing (internal morphology) is disturbed by inclusion of these HV units. 6,[8][9][10][11] Additionally, NMR evidence indicates that from 20-40% HV total contents in the copolymer structure, some segments with relative higher HV units, are partially excluded from the PHB lattice. 12 From the polyhydroxyalkanoates data shown in Table 1, it can be inferred that the glass transition temperature (Tg), measured for copolymers with 14 and 22 mole % HV contents, were lower than the predicted by the Fox's equation (1/Tg = W PHB /Tg PHB + W HV /Tg HV, where W is the content of the polymer).…”

Section: Bulk Propertiesmentioning

confidence: 99%

Structural impact of hydroxyvalerate in polyhydroxyalkanoates (PHAscl) dense film monitored by XPS and photothermal methods

Silva¹,

Vargas²,

Poley³

et al. 2005

J. Braz. Chem. Soc.

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Filmes densos de poli(3-hidrobutirato) e poli(3-hidroxibutirato-co-3-hidroxivalerato) com espessuras de 90 µm foram obtidos utilizando o método "casting" de deposição e caracterizados por espectroscopia de fotoelétrons, calorimetria diferencial e métodos fotoacústicos. As frações molares de hidroxivalerato utilizadas foram de 8, 14 e 22 % molar. Seguindo uma mesma tendência, a capacidade térmica específica e a temperatura de transição vítrea diminuem com o aumento da concentração de hidroxivalerato.Poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) polymer dense films with thickness of 90 µm were obtained by the casting method and characterized using X-ray photoelectron spectroscopy, differential scanning calorimetric and photo-thermal methods. The HV molar fractions in the copolymer structure were 8, 14 and 22 mol %. The measured specific thermal capacity and the glass transition temperature of the P3(HB-co-x%HV) decrease for increasing hydroxyvalerate content following a similar trend. Keywords: polymers, photoacoustics, XPS, thermal properties IntroductionIn the last years, science and industry have given special attention to the development of biodegradable polymer materials as consequence of today ecological problems caused by most of the chemical and petrochemical synthesized polymers disposed in the environment. 1 Chemically and petrochemically synthesized polymers are generally resistant to enzymatic attack. Although some of these synthetic polymers can be microbiologically degraded, the process of degradation is slow in contrast to the biodegradability of the polymers of biological origin. 2 The biodegradability is not the only characteristic that makes the polymers of biological origin attractive, also their biosynthesis from renewable carbon sources, based on agricultural products, allows a sustainable closed process for the production and use of such polymers.One important family of the biologically produced thermoplastic polyesters is formed by the polyhydroxyalkanoaes (PHAs). Important members of this family are the P3HB and P(3HB-co-3HV)copolymers synthesized and intracellularly stored by numerous prokaryotes by well know fermentation process. The stereoregularity of P3HB makes it a highly crystalline material having melting point of 177 o C, close to that of polypropylene among others similarities, although the biopolymer is stiffer and more brittle. 3,4 The P(3HB-co-3HV) chains also show crystalline conformations and the co-monomer distribution is statistically random. The properties of the copolymers of 3HB and 3 HV changes depending on their HV contents. The minimum of the melting point (≅80 o C, pseudoeutectic point) of the copolymers is observed for a 30% mole fraction of HV. 5,6 The accurate determination of the thermal properties of polymers and particularly of PHAs is of fundamental importance in many processes and engineering projects aiming at the expansion of the uses of these biodegradable materials. In the present work, the effect of HV contents in the P(3HB-co-...

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Section: Bulk Propertiesmentioning

confidence: 99%

Structural impact of hydroxyvalerate in polyhydroxyalkanoates (PHAscl) dense film monitored by XPS and photothermal methods

Silva¹,

Vargas²,

Poley³

et al. 2005

J. Braz. Chem. Soc.

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“…Thus the PA spectroscopic technique has been widely utilized to investigate the non-radiative de-excitation and photo-induced thermal conversion processes. The PA spectroscopic techniques have also proven to be a very sensitive tool for studying the thermal properties of materials [1][2][3][4][5] such as thermal diffusivity and thermal conductivity with sufficient accuracy. [6][7][8] In addition, various PA techniques have been applied to measure the composition-dependent optical energy gap, optical absorption coefficient, and thermal properties and carrier transport properties in glasses, 9-11 alloys, 12 metal oxides, 13 ion implantations, 14,15 and semiconductors.…”

Section: Introductionmentioning

confidence: 99%

Determination of Doping Density in GaAs Semiconductor by Wavelength-Dependent Photoacoustic Spectroscopy

Lim

Choi

Boo

et al. 2014

Bulletin of the Korean Chemical Society

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The wavelength dependence of the photoacoustic signal for n-type GaAs semiconductors in the region of the band-gap energies was investigated. The significant changes in the phase and amplitude of the photoacoustic signal near the band-gap absorption wavelengths were observed to occur when the Si-doping densities in GaAs were varied. Particularly, the first derivatives of the photoacoustic phase vs. wavelength graphs were evaluated and fitted with single Gaussian functions. The peak centers and the widths of the Gaussian curves clearly showed linear relationships with the log values of the Si-doping densities in n-type GaAs semiconductors. It is proposed that the wavelength-dependent PA spectroscopy can be used as a simple and nondestructive method for measuring the doping densities in bulk semiconductors.

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“…The optical absorption maxima for these phycobiliproteins are 566 nm for R-PE, 621 nm for C-PC and 651 nm for APC [1,2]. The photoacoustic spectroscopy (PAS) technique has been used in a variety of materials [3][4][5][6][7]. In this work photoacoustic spectroscopy (PAS) was applied to investigate the phycobiliproteins expression in an eukaryotic red algae: Gracilaria chilensis.…”

Section: Introductionmentioning

confidence: 99%

In situphotoacoustic spectroscopy of phycobiliproteins inGracilaria chilensis

et al. 2005

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Abstract. Phycobiliproteins, the main polypeptidic components of the phycobilisomes (PBS), are biological macromolecules arranged in complex interaction systems to perform light harvesting and conduction. The optical properties of these systems can hardly be studied by conventional spectroscopic techniques. Furthermore this techniques also involve laborious chemical extraction methods. Photoacoustic (PA) spectroscopy was successfully applied to an in situ study of the phycobiliproteins expression in the eukaryotic red algae: Gracilaria chilensis.

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Photoacoustic and related photothermal techniques

Cited by 412 publications

References 231 publications

Structural impact of hydroxyvalerate in polyhydroxyalkanoates (PHAscl) dense film monitored by XPS and photothermal methods

Structural impact of hydroxyvalerate in polyhydroxyalkanoates (PHAscl) dense film monitored by XPS and photothermal methods

Determination of Doping Density in GaAs Semiconductor by Wavelength-Dependent Photoacoustic Spectroscopy

In situphotoacoustic spectroscopy of phycobiliproteins inGracilaria chilensis

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