Neutron scattering study on dynamics of water molecules confined in MCM-41

Quasi-elastic neutron scattering (QENS) spectra of water-filled MCM-41 samples having different pore sizes (pore diameters: 2.14 and 2.84 nm) were measured over the temperature range 200-298 K and analyzed by a model in which contributions of translational and rotational diffusions of water molecules are expressed by a linear combination of Lorentzian functions (Teixeira et al., 1985). The results indicated that the translational diffusion is decelerated by confinement and that the deceleration increases with a decrease in pore size. QENS spectra of water-filled MCM-41 samples having the same pore sizes (pore diameter: 3.36 nm) but a different amount of the hydroxyl groups (0.7 and 2.6 OH's/nm²) were also measured over the temperature range 220-298 K. It was found that the vibrational amplitude of water molecules in MCM-41 increases with increasing amount of the surface hydroxyls, which implies that the hydrogen-bond network of confined water is distorted by interaction with the surface hydroxyls.