Relaxation and dynamical properties of water in partially filled porous materials using NMR techniques

Abstract

The study of relaxation times of NMR active nuclei in liquids confined to pore structures allows characterization of the geometry of the open volume providing information regarding its homogeneity, spatial distribution, and tortuosity. Experiments performed on samples containing different amounts of fluid can probe the degree of homogeneity at smaller and smaller length scales, permitting a determination of the intrinsic nature of the liquid-solid interaction responsible for the observed enhancement of the relaxation rates. The results of longitudinal and transverse relaxation experiments on water filling a microporous leached borosilicate glass are discussed. Particular emphasis is devoted to relaxation and dynamical properties at sub-monolayer coverage. This is discussed in the context of the molecular interaction at the liquid-solid interface. The results are interpreted in terms of anisotropic rotation of the adsorbed molecules and the characteristic times of such motion are extracted. This is compared with the molecular translation degree of freedom derived from NMR pulsed field gradient techniques suggesting that the two types of motion are closely related.