Water in spherical, cylindrical and slitlike pores

Abstract

Adsorbed water in slitlike micropores of ca. 1.0 nm width of jarosite and alunite (nanopile) was distinguished by the dielectric properties and H NMR parameters for mono-, bi-, and trimolecular layers. In a monolayer water molecules seem to have a mode of rotational motion and show no phase transition in the rage 30 ~- 80 °C, in a multilayer have a mode of translational motion and freeze at about -30 °C and in a three layer (q=1.5) in the 1 nm slitlike micropores change their motional mode from rotation to translation across about -30 °C. The extreme immobilization of water molecules at q=1.5, which was suggested by a maximum dielectric relaxation time and very small heat of fusion, was attributed to a filling of the slitlike micropores with water molecules which bridge the first layers on both walls of the micropores through hydrogen bonding. Water adsorbed on the inner and outer surfaces of nanotubules, imogolite (pore diameter d=1.0 nm) and chrysotile (d= 7 nm), showed two NMR relaxation rates. The fast and slow relaxation rate for chrysotile are ascribed to water on an inner and outer surface, respectively. Water with fast relaxation mode had three states at the higher coverage of q>3 and are adsorbed in the mesopores by capillary condensation to form a liquid phase that may be supercooled down to -60 °C. The slow relaxation rate for imogolite seems to arise from water immobilized on an inner surface of the cylindrical micropores. Water on a nanobaloon, allophane (d=1.5-3 nm) having small holes (0.3-0.5 nm in diameter) on the wall, also has two relaxation rates. The longitudinal relaxation of water in the micropores is faster in the order of spherical>cylindrical>slitlike.