Interlayer Water Molecules in Vanadium Pentoxide Hydrate. 8. Dynamic Properties by Quasi-Elastic Neutron Scattering

Abstract

The dynamics of water molecules in the layered vanadium pentoxide hydrate, V2O5·nH2O, were studied by quasi-elastic neutron scattering (QENS) measurements. Heterogeneity of the dynamic properties was confirmed by α-relaxation model analysis. Translational diffusion of monolayer and double-layer water molecules is by site-to-site diffusion and is reduced relative to that of bulk water. Water molecules lose their mobility markedly and solidify with decreasing temperature. However, mobile water remains at 253 K. Rotational diffusion coefficients are unaffected by confinement and are very similar to the bulk values determined at temperatures in the range 253−298 K. The dynamic speed characterized by QENS is much faster than that expected from the data determined by deuterium NMR (DNMR) measurements at low temperatures.

Interlayer water molecules in vanadium pentoxide hydrate. IX. Anisotropic translational diffusion leading to anisotropic ac conductivity

“…In contrast to previous work, 2,14 in which V 2 O 5 · nH 2 O was freeze dried from a thick sol under a stage-free condition, the QENS spectra of the monolayer water are sharper than those previously reported, indicating a marked slowing down of the translational motion. Fitting of the stretched exponential function has not been successful.…”

“…14 The relaxation time of the rotational motion of the interlayer water molecules was similar to that of bulk water molecules for both monolayer and double-layer water molecules. 14 The relaxation time of the rotational motion of the interlayer water molecules was similar to that of bulk water molecules for both monolayer and double-layer water molecules.…”

“…14 Here, the observed QENS spectra provide information on the translational motion of the water molecules in the layered V 2 O 5 · nH 2 O. The term A␦͑͒ accounts for the contribution of immobile species, and A is an elastic incoherent structure factor ͑EISF͒.…”

Hydration of Ions in Confined Spaces and Ion Recognition Selectivity

“…It is known that materials confined in nanospaces show structures and/or dynamics different from those exhibited in bulk. [1][2][3][4][5][6][7][8][9][10][11] Such unusual properties, which become more apparent as the size of the space decreases, partly come from the effects of the walls surrounding the spaces. 2,6 The interaction of compounds with the wall becomes more dominant with decreasing size of the space.…”

“…In addition, molecular aggregates and clusters cannot retain their stable sizes in such narrow spaces and show unusual physicochemical features as a result. Various compounds are accommodated in confined spaces, and their molecular structures and dynamics therein have been studied by X-ray and neutron scattering, [3][4][5] spectroscopy, 6,7 and computer simulations. 9,10 An interface, which can be considered as a space twodimensionally confined between two phases, has received increasing attention in analytical sciences.…”