Publication: Estudio por fluorescencia intrínseca y FT-NIR del efecto de la presencia de nanopartículas de SiO2 en las transiciones térmicas del PS
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2010
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2010
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Abstract
Se ha estudiado el efecto de la presencia de nanopartículas de sílice en la dinámica molecular de poliestireno. Para ello, mediante la espectroscopía de fluorescencia y espectroscopía infrarroja por transformada de Fourier en el infrarrojo cercano (FT-NIR), se han analizado las transiciones térmicas del poliestireno, PS, y del material nanocompuesto basado en PS y nanopartículas de sílice. El material nanocompuesto fue preparado mediante molienda mecánica de alta energía (High Energy Ball Milling, HEBM) durante distintos tiempos de molienda (1, 2, 4, 6 y 8 horas). Se prepararon muestras molidas tanto con nanopartículas, como sin nanopartículas. La respuesta fluorescente intrínseca del PS debido a la presencia del anillo bencénico, hace posible un seguimiento de la misma en función de la temperatura (desde 30ºC hasta 150ºC). De esta manera, se pudo estudiar la influencia del tiempo de molienda en las transiciones térmicas del PS, y de la influencia de la presencia de nanopartículas en estas transiciones. Este estudio se ha llevado a cabo mediante la representación de dos parámetros fotofísicos en función de la temperatura: (i) el primer momento de la banda de emisión <v> y (ii) la intensidad de fluorescencia integrada. En el primer caso, se observaron dos cambios de pendiente en torno a 80ºC y 120ºC. También se representó el Logaritmo del segundo parámetro fotofísico frente a la inversa de la temperatura observándose dos transiciones térmicas, además de la transición vítrea. El estudio mediante FT-NIR en las mismas condiciones que el de fluorescencia, nos permitió conocer la influencia de la presencia de nanopartículas a escala molecular. Se observó que con el tiempo de molienda la evolución de las bandas de absorción de los enlaces aromáticos con la temperatura es más sensible a la de las bandas asociadas a enlaces alifáticos. También se ha observado un cambio de tendencia en las áreas de las bandas con la temperatura al moler el material sin nanopartículas.---------------------------------------------------------------------------------------------------------------------
The effect of the silica nanoparticles in the molecular dynamic of the polystyrene has been analyzed in this project. By using fluorescence spectroscopy and FT-NIR, the thermal transitions of the polystyrene, PS, and the nanocomposite based on PS and silica nanoparticles have been examined. The nanocomposite material was prepared by a High Energy Ball Milling (HEBM) in different periods of time (1, 2, 4, 6 and 8 hours). The milling samples were prepared with and without nanoparticles. The intrinsic fluorescence response of PS due to the presence of the phenyl group allows studying the polymer dynamics based on the motion canges suffer by the macromolecules as a function of temperature (from 30ºC to 150ºC). In this way, the influence upon the time milling on the PS’s thermal transitions and on the presence of nanoparticles was possible to study. This study was carried out by the representation of two photophysical parameters based on temperature: (i) the first moment of the emission band <v> and (ii) the integrated intensity of fluorescence. In the first case, two slope variations were observed at 80ºC and 120ºC. The logarithm of the second photphysical parameter was also represented versus the inverse of the temperature, showing two thermal transitions and the glass transition. The FT-NIR study, carried out in the same conditions than the fluorescence one, allowed us to know the influence of the presence of nanoparticles in a molecular level. It was observed that after milling, the evolution with temperature of the absorption IR bands associated to the aromatic bonds is more sensible than the evolution of bands associated to the aliphatic bonds. Besides, a change in the tendency of the absorbance with temperature was observed comparing milled simple with non milled samples.
The effect of the silica nanoparticles in the molecular dynamic of the polystyrene has been analyzed in this project. By using fluorescence spectroscopy and FT-NIR, the thermal transitions of the polystyrene, PS, and the nanocomposite based on PS and silica nanoparticles have been examined. The nanocomposite material was prepared by a High Energy Ball Milling (HEBM) in different periods of time (1, 2, 4, 6 and 8 hours). The milling samples were prepared with and without nanoparticles. The intrinsic fluorescence response of PS due to the presence of the phenyl group allows studying the polymer dynamics based on the motion canges suffer by the macromolecules as a function of temperature (from 30ºC to 150ºC). In this way, the influence upon the time milling on the PS’s thermal transitions and on the presence of nanoparticles was possible to study. This study was carried out by the representation of two photophysical parameters based on temperature: (i) the first moment of the emission band <v> and (ii) the integrated intensity of fluorescence. In the first case, two slope variations were observed at 80ºC and 120ºC. The logarithm of the second photphysical parameter was also represented versus the inverse of the temperature, showing two thermal transitions and the glass transition. The FT-NIR study, carried out in the same conditions than the fluorescence one, allowed us to know the influence of the presence of nanoparticles in a molecular level. It was observed that after milling, the evolution with temperature of the absorption IR bands associated to the aromatic bonds is more sensible than the evolution of bands associated to the aliphatic bonds. Besides, a change in the tendency of the absorbance with temperature was observed comparing milled simple with non milled samples.
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Transiciones térmicas, Poliestireno, Materiales nanocompuestos, Espectroscopía de fluorescencia, Espectroscopía infrarroja, Transformadas de Fourier