Water dynamics in bulk and dispersed in silica CaCl2 hydrates studied by neutron scattering methods

Quasi-elastic and inelastic neutron scattering techniques have been used to study the dynamics of water in CaCl2 · nH2O (n = 1/3,2,4,6,9) hydrates dispersed in silica, in comparison with the bulk hydrates. Inelastic scattering shows that the water molecules in dispersed hydrates are in an amorphous state. Quasi-elastic scattering indicates a higher mobility of water in the hydrates dispersed in silica, compared to bulk hydrates. The self-diffusivity of water in the dispersed hydrates increases with water concentration, while remaining below the one of pure water. The neutron and pulsed-field gradient NMR diffusivities are similar, which indicates that the hydrates form a thin and continuous layer on the pore walls of silica.