Restricted molecular diffusion in the vicinity of a reflective wall as probed by NMR measurements using radio-frequency field gradients

Radiofrequency field gradients (B1 gradients) are known to be insensitive to the background static field gradients (B0 gradients) which arise from zones of different magnetic susceptibility within the object under investigation. This feature is exploited here in order to detect restricted diffusion at the edge of a standard cylindrical glass tube containing water. A simple method based on B1 gradients has been devised for producing a spatially resolved map in which translational diffusion coefficients are displayed along the third dimension. A decrease of the apparent self-diffusion coefficient at the liquid–glass boundary is indeed observed and explained by a simple theory used previously in the case of very rapidly diffusing systems [Y.Q. Song, B.M. Goodson, B. Sheridan, T.M. de Swiet, A. Pines, J. Chem. Phys. 108 (1998) 6233].