High-resolution inelastic neutron scattering from water in mesoporous silica.

High-resolution inelastic neutron scattering measurements of the molecular dynamics of water confined to a porous host, the molecular sieve known as MCM-41, which has a hexagonal array of parallel pores with average pore diameter of 27 Angstrom, are reported. Previous neutron measurements probing higher-energy transfers, and thus shorter time scales, have been analyzed with both a rotation-translation diffusion model and a stretched exponential intermediate scattering function. The dynamics on longer time scales presented here are modeled well with a stretched exponential relaxation in a confining geometry. The observed molecular dynamics of water are three orders of magnitude slower than has been previously reported for water confined in MCM-41.