Diffusion in porous materials as probed by pulsed gradient NMR measurements

Due to recent activity involving diffusion measurements using pulsed gradient spin echo techniques, both experimental and theoretical, we now have a better understanding of diffusion of fluid molecules in a large class of natural and artificial porous media. At short times, the restrictions cause deviations from free diffusion that depend only on local properties of the pore-grain interface. This allows quantities such as the time-dependent diffusion coefficient and the return to the origin probability to be calculated exactly, and these results have been experimentally verified. At longer times, diffraction-like effects are observed in the measured momentum-space diffusion propagator, which can be understood in model systems. In general, it is better understood how diffusion measurements may be used to probe the microgeometry of porous media.