No abstract

We have investigated the dynamics of water molecules in zeolites NaA and NaX by high-resolution quasielastic neutron scattering methods. Between 260 and 310 K, the local translational diffusive motion of water in the zeolites is one to two orders of magnitude slower than in bulk water. The Q dependence of the scattering shows effects of confinement and the presence of both relatively mobile and immobile molecules. The speed of the diffusive motion depends strongly on hydration level. Comparison with other hydrated siliceous materials indicates that the host charge per water molecule is a major factor in determining the time scale of diffusion.

Investigations on the lattice dynamics of muscovite and vermiculite have been carried out by inelastic neutron scattering and Raman scattering. In the neutron measurements, dispersion curves for the out-of-plane and in-plane LA and TA phonons were fully obtained for muscovite, while more limited data were obtained for Mg vermiculite. Sound velocities were estimated from the slopes of the dispersion curves. Raman-scattering experiments revealed an interlayer shearing mode in Na and Sr vermiculites in the 0-water-layer hydration state. The intercalated water molecules in Na and Sr vermiculites exhibited a broad Raman feature (OH stretching vibrations) at 3450 cm with a full width at half maximum of -300 cm '. In addition, relatively sharp Raman peaks from the inner-layer hydroxyls in the host octahedral layers were found at -3700 cm '. These peaks were sensitive to the hydration state or charge in the intercalated layer.

Hydration phase transitions in Na vermiculite, a specific example of expandable 2:1 layered silicates, were examined as a function of temperature at a constant water-vapor pressure by x-ray diffraction. The samples exhibited well-defined 0-, 1-, and 2-water-layer hydration states (WLHS s) with the basal spacings of 9.81, 11. 84, and 14.89 A, respectively. The transitions between the hydration states were found to be first order, evidenced by a two-phase coexistence and large hysteresis.Substantial elastic deformation, which involves rotations of the tetragonal bases in the host silicate layers, was observed during the transitions. It was concluded that elastic distortion in the host layers may be responsible for the hydration phase transitions. In addition, formation of a (2a X2b) superlattice specific to the 1-WLHS was found. A new interpretation of the previous Raman data from 1-WLHS Na vermiculite is also presented.

We report the first explicit measurement on the profile of a spreading edge of nonvolatile liquid, in support of the theory of Hervet and de Gennes on a one-dimensional thin spreading edge. From the laser light interference patterns, the meniscus shape of the edge was reconstructed and the advancing dynamic contact angle was measured. The meniscus shape and the contact angle are in good agreement with their theory. The meniscus shape obtained at several different capillary numbers can be collapsed into one dimensionless curve, using their scaling laws.