Abstract :
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 origil 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.
