Diffusive Relaxations and Vibrational Properties of Water and H-bonded Systems in Confined State by Neutrons and Light Scattering:  State of the Art

Abstract

A detailed spectroscopic analysis is presented in order to study the reorientational and vibrational dynamics of water and other fundamental H-bonded systems: ethylene glycol (HO−CH2−CH2−OH) and its homologous species, such as ethylene glycol monomethyl ether (CH3O−CH2−CH2−OH) and ethylene glycol dimethyl 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 Å interconnected cylindrical pores. The use of different spectroscopic techniques, light scattering (Rayleigh wing and Raman scattering), FT-IR absorption, neutron scattering (incoherent quasi elastic and inelastic neutron scattering, IQENS and IINS, respectively) allow the marking of different dynamical parameters, with different probes being used to investigate H-bonded systems. The clear influence of the confinement on the mobility of the studied liquids, with a dramatic frozen-in observed effect respect to the bulk state, is evidenced and compared with literature results. Furthermore, a surface−liquid potential well induces strong modifications of the local symmetry of the vibrational groups (e.g., the active OH stretching groups) involved in the interaction, giving rise to anharmonic effects (red shift, band enlargement) that depend on the nature of the surface (hydrophobic or hydrophilic) and on the nature of guest liquids (wetting or nonwetting).

Strain-dependent fractional molecular diffusion in humid spider silk fibres

“…The higher the position of the libration peak is in absolute energy values, the stronger the adsorbed water is geometrically confined [40]. Another peak can be observed near 230 meV.…”

Temperature and Size Effects on Structural and Dynamical Properties of Water Confined in 1 – 10 nm-scale Pores Using Proton NMR Spectroscopy

“…[5][6][7][8] Over the past decades, the effects of confinement in mesoporous silica materials with 1 nm-scale spaces on microscopic properties of water molecules have been examined using experimental and theoretical methods. [9][10][11][12][13][14][15] These studies have clarified that the hydrogen bonding structures of water molecules near the pore surface are distorted and perturbed due to water-surface interactions or topological effects even at ambient temperatures. Moreover, since water confined in 1 nmscale spaces adopts a supercooled state below the freezing point of bulk water, microscopic properties and liquid/solid phase transition of confined water have been investigated in a considerably low temperature region.…”

Hydrogen bonding in the Raman O–H stretching band of propylene glycol in nanometre-confined space: surface interactions and finite-size effects

“…Going to higher frequencies, the sub-band ω 2 is ascribed to molecules that donate and accept H-bonds, so giving rise to trimers and more First of all, for both bulk and confined PG, an increasing temperature causes the diminishing of the relative areas I 1 and I 2 favouring the increasing of I 3 and I 4 . In terms of number of PG molecules belonging to the appropriate association state this means that the thermal motion is high enough to break the intramolecular H-bond of closed monomeric structures allowing them to open, and, on the other side, it contributes to destroy high-connectivity arrangements, favouring less coordinated structures, as expected.…”

“…For the cleaning and filling procedure of the glasses the reader can refer to Ref. [4]. The Raman spectra were collected, in the -10°C÷+60°C range, by a high-resolution triple monochromator SPEX RAMALOG 5.…”

“…The performed experiments [2][3], however, have often lead to contradictory results, explained in terms of a competitive balance between the architecture of the confining host and the interaction of the confined molecules with the internal surface [4]. It is commonly believed [1] that only surface interactions, that highly affect the interfacial layer causing the formation of H-bonds and physisorption, contribute to slow-down the relaxational motions with respect to the corresponding bulk systems, giving rise to a dramatic increase of the glass transition temperature T g .…”