QINS studies of water diffusion in Na-Montmorillonite

Complete text of publication follows. The rotational and translational motion of interlayer water was investigated in Na-Montmorillonite as a function of the humidity (one-, two- and three-layers). Partially orientated samples produced by deposition onto a filter under pressure were used. Measurements were made at two different resolutions 120 μeV and 36 μeV. In order to observe the anisotropy, measurements with sample orientations of 135 and 45 degree were made with respect to the incident beam corresponding to Q-parallel and Q-perpendicular to the clay layers. The fitting procedure consists of an elastic term based on a fit to an analogous D2O hydrated sample and a quasielastic term containing both rotational and translational contributions (1). At low resolution with Q-parallel a rotational broadening was observed that increases, indicating increasing water mobility, as the water content and hence the layer spacing increases. For the three-layer hydrate with the two different orientations the broadening is the same showing no measurable anisotropy of the rotational motion. At high resolution an additional broadening was seen due to translational diffusion of a similar magnitude to that measured previously for Li-Montmorillonite (2). We are currently refining our data analysis in order to determine whether the anisotropy of the translational motion with respect to the orientation of the clay is measurable. (author)