No 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 (ω 1 ), 3470 (ω 2 ), and 3590 cm -1 (ω 3 ), 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.

Uncharged star polymers having a porphyrin core and four poly(ethylene glycol)methyl ether (PEGME) arms have been synthesized and investigated (through the study of the structural and dynamical properties) as a function of the molecular mass of the arms, in different thermodynamic conditions. Molecules with short PEGME arms are insoluble in water, whereas in the presence of long PEGME chains, the star polymers are water-soluble; for the intermediate length of the arms, the building up of large rigid monodisperse aggregates, driven by the diffusion limit aggregation mechanism, has been observed by means of static and dynamic light scattering. These aggregated systems, whose sizes are modulated by changing the pH and triggered by the chain flexibility, can be well described in terms of the DLVO interparticle potential in the frame of the colloidal theory.

Depolarized Rayleigh and low frequency Raman scattering data in bulk supercooled water are presented. The measurements, performed from the normal region down to −26.95 °C for the first time, allow a quantitative data analysis and reveal the existence of a fine structure of the central contribution. We have identified a ‘‘fast’’ and ‘‘slow’’ contribution whose intensities show an opposite behavior as a function of temperature. Such a behavior is understood as a decay of local order due to the H bond. The spectral density function, as derived from the depolarized Raman data, shows the presence of acoustical and intermolecular optical contributions characteristic of many structured disordered materials. A critical comparison with molecular dynamics (MD) and neutron scattering results is also presented.