SURFACE DIFFUSION OF LIQUIDS IN DISORDERED NANOPORES AND MATERIALS: A FIELD CYCLING RELAXOMETRY APPROACH

Abstract

Abstract Proton nuclear magnetic relaxation dispersion experiments show remarkable differences between water and aprotic liquids in contact with nanoporous glass surfaces containing trace paramagnetic impurities. We have interpreted the data with a theory of nuclear spin relaxation appropriate to the case of a mobile liquid dipolar spin diffusing in a quasi two dimensional model porous system in the presence of rare paramagnetic impurities fixed at the surface of the pores. The theory is tested at several temperatures using acetone, acetonitrile, dimethylformamide, and dimethylsulfoxide on microporous chromatographic glass beads that have paramagnetic ion impurities at the level of 40 ppm. The data obtained for water show that surface enhanced water proton diffusion permits the proton to explore a greater spatial extent of the pore, which results in an apparent 1-dimensional model for the diffusive motions of the water that dominate nuclear spin relaxation