Résumé
The effect of temperature in the range 0-150degreesC was studied for homo-ionic montmorillonite clays with Na+ and Cs+ compensating ions in low hydration states. Monte Carlo and molecular dynamics simulations were employed to provide both static and dynamic information concerning the interlayer ions and water molecules, and emphasis was laid on the temperature activation of the diffusion coefficients. Principal structural changes were limited to the interlayer water phase, In the monohydrated systems, neither of the cations was seen to enter into the hexagonal cavities of the clay. Cs+ exhibited clear site-to-site diffusion between sites allowing coordination to six oxygen atoms of the clay sheets, this behaviour persisting to high temperatures. Preferential sites for the Na+ counterion were much less well-defined, even at low temperatures. The behaviour of the water phase in the monohydrated states was similar for the two ions. A rapid approach to bulk dynamics was seen in the transition from monohydrated to bihydrated Na-montmorillonite. A detailed quantitative comparison of the temperature activation of diffusion for a two-dimensional water phase and three-dimensional bulk water is presented for the first time.