Incoherent quasi-elastic neutron scattering (IQENS) and Fourier-transform infrared (FT-IR) absorption measurements have been employed to investigate the diffusional and vibrational dynamics on water confined in a NaA zeolitic matrix. In analogy with the results of a recent quasi-elastic neutron scattering experiment on water confined in a sol−gel silica glass (GelSil), reported in the preceding paper (Crupi, V.; Majolino, D.; Migliardo, P.; Venuti, V. J. Phys. Chem. B 2002, 106, 10 884), the diffusive process reveals a rather wide distribution of relaxation times. Furthermore, we observed a Q-dependence of the mean relaxation time τ, which does not disagree with the mode coupling theory for associated liquids. As far as vibrational dynamics is concerned, the spectral substructure of the O−H stretching band in the IR spectra has been explained postulating the existence of three major components peaked at approximately 3290 (ω1), 3470 (ω2), and 3590 cm-1 (ω3), having different spectral and dynamical properties traced over the full temperature-investigated range. These data, compared with the IINS spectra reported, in the case of water in GelSil, in our first paper, will allow us to show the structure maker role played by the zeolite for confined water as opposed to the structure breaker character observed in the case of the GelSil matrix.

Neutron scattering study and dynamic properties of hydrogen-bonded liquids in mesoscopic confinement. 2. The zeolitic water case

CRUPI, Vincenza;MAJOLINO, Domenico;MIGLIARDO, Placido;VENUTI, Valentina;WANDERLINGH, Ulderico;
2004

Abstract

Incoherent quasi-elastic neutron scattering (IQENS) and Fourier-transform infrared (FT-IR) absorption measurements have been employed to investigate the diffusional and vibrational dynamics on water confined in a NaA zeolitic matrix. In analogy with the results of a recent quasi-elastic neutron scattering experiment on water confined in a sol−gel silica glass (GelSil), reported in the preceding paper (Crupi, V.; Majolino, D.; Migliardo, P.; Venuti, V. J. Phys. Chem. B 2002, 106, 10 884), the diffusive process reveals a rather wide distribution of relaxation times. Furthermore, we observed a Q-dependence of the mean relaxation time τ, which does not disagree with the mode coupling theory for associated liquids. As far as vibrational dynamics is concerned, the spectral substructure of the O−H stretching band in the IR spectra has been explained postulating the existence of three major components peaked at approximately 3290 (ω1), 3470 (ω2), and 3590 cm-1 (ω3), having different spectral and dynamical properties traced over the full temperature-investigated range. These data, compared with the IINS spectra reported, in the case of water in GelSil, in our first paper, will allow us to show the structure maker role played by the zeolite for confined water as opposed to the structure breaker character observed in the case of the GelSil matrix.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11570/1584900
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