Abstract
A quasi-elastic neutron scattering study of water dynamics confined in a model clay system (a synthetichectorite with Na+ compensating counterions) is presented. The neutron spin echo (NSE) data obtained atambient temperature for the monohydrated and bihydrated hectorite powder areanalysed with the help of models taking into account the anisotropy of the system. Apowder-averaged two-dimensional (2D) diffusion model applied to the monohydrated stateyields a 2D diffusion coefficient in the plane of the clay layers () of 2.8 × 10−10 m2 s−1, where an isotropic analysis of the data would have underestimated the diffusion coefficientby approximately 25%. In the case of the bihydrated state, the analysis by amodel including a possible diffusion perpendicular to the clay layers () leads to a range of values for between 3.5 and 8.7 × 10−10 m2 s−1, depending on the ratio . We conclude that simple isotropic analysis can only give a rough estimate (order ofmagnitude) of the water dynamics in the medium.
Published Version
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