Observations of diffusion of fluids in porous solids by pulsed field gradient NMR

The diffusion properties of water and n-decane in porous alumina have been studied using pulsed field gradient nuclear magnetic resonance (PFGNMR). Use of the stimulated echo experiment has been found to be advantageous in these systems because the 1H T1's of both fluids in the porous alumina are much larger than the corresponding T2's. Variation of the time between the gradient pulses (the diffusion time, Δ) allows the technique to access molecular diffusion over a range of scales of translational displacements. The echo attenuations observed are non-exponential functions of the diffusion time. Various models could be considered to represent the void space. However, the diffusional behaviour suggests that a highly anisotropic structure which produces an apparent effective dimensionality for the diffusion of the order of 2 might be most appropriate. (author). 9 refs.; 7 figs