Two-dimensional T(2)-T(2) NMR relaxation exchange spectroscopy has been applied to model porous media composed of mixtures of nonporous borosilicate and soda lime glass spheres in water. The spheres had a mean diameter of 100 microm, thus providing an approximately constant characteristic pore dimension throughout the structures, while the use of two glass types ensured that water in different pore-space regions had significantly different T(2) relaxation rates. The packed beds were constructed in various ways with controlled glass type domain sizes to rigorously validate a model for region-to-region exchange of water. From the determined exchange times, the corresponding length scales were calculated based on the molecular self-diffusion of water; these agreed to better than +/-25% with the expected domain sizes. Furthermore, exchange distances on the order of the pore size were observed in thoroughly mixed systems. Depending on the relaxation rates present in the sample, this technique can provide estimates of length scales ranging from microns to millimeters.

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Nuclear magnetic resonance (NMR) two-dimensional relaxation correlation experiments have been used to study an industrially relevant formulation of surfactant multilamellar vesicles (MLVs) in an aqueous solution. By correlating transverse T2 relaxation measurements before and after a storage interval, diffusive exchange of water molecules between domains can be observed. Two average exchange times of 0.04 and 0.83 s were determined by solving the one-dimensional Fredholm integral form of a model for region-to-region exchange. Diffusion coefficients for the restricted and free water fractions within the mixture determined via chemically selective pulsed field gradient (PFG) NMR measurements allowed exchange distances of 6.2 and 81 microm to be determined from the exchange times. These exchange distances are associated with the average MLV diameter and speculatively with the size of MLV clusters, respectively.