Diffusive relaxations and vibrational properties of water and H-bonded systems in confined state by neutrons and light scattering: State of the art

A detailed spectroscopic analysis is presented in order to study the reorie ntational and vibrational dynamics of water and other fundamental H-bonded systems: ethylene glycol (HO-CH2-CH2-OH) and its homologous species, such a s ethylene glycol monomethyl ether (CH3O-CH2-CH2-OH) and ethylene glycol di methyl ether (CH3O-CH2-CH2-OCH3), propylene glycol (HO-CH(CH3)-CH2-OH) and its oligomers, that are confined in a matrix of sol-gel porous glasses with 26 Angstrom interconnected cylindrical pores. The use of different spectro scopic techniques, light scattering (Rayleigh wing and Raman scattering), F T-IR absorption, neutron scattering (incoherent quasi elastic and inelastic neutron scattering, IQENS and IINS, respectively) allow the marking of dif ferent dynamical parameters, with different probes being used to investigat e H-bonded systems. The clear influence of the confinement on the mobility of the studied liquids, with a dramatic frozen-in observed effect respect t o the bulk state, is evidenced and compared with literature results. Furthe rmore, a surface-liquid potential well induces strong modifications of the local symmetry of the vibrational groups (e.g., the active OH stretching gr oups) involved in the interaction, giving rise to anharmonic effects (red s hift, band enlargement) that depend on the nature of the surface (hydrophob ic or hydrophilic) and on the nature of guest liquids (wetting or nonwettin g).