Water diffusion in a synthetic hectorite by neutron scattering—beyond the isotropic translational model

• Published in: Journal of physics. Condensed matter 2008-03, Vol.20 (10), p.104205-104205 (10)
• Main Authors: Marry, V, Malikova, N, Cadène, A, Dubois, E, Durand-Vidal, S, Turq, P, Breu, J, Longeville, S, Zanotti, J-M
• Format: Article
• Language: English
• Subjects: Chemical Physics; Condensed matter: structure, mechanical and thermal properties; Diffusion in solids; Exact sciences and technology; Physics; Transport properties of condensed matter (nonelectronic)
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/20/10/104205

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