Hexane Self-Diffusion in Bed of Glass Spheres. Testing Applicability Range of the Pore-Hopping Model
Abstrakt
PFG NMR experiment is in principle capable to provide important transport-structural parameters of system consisting of a liquid confined in a porous matrix such as surface- to-volume ratio and tortuosity. The apparent diffusion coefficient is easily obtained in the case of Gaussian shape of the diffusion propagator.
Dependence of these values on the diffusion time in a short time limit is then used to derive the surface-to-volume ratio by means of the formula derived by Mitra. Tortuosity is, on the other hand, derived from the long time limit of the apparent self-diffusion coefficient.
The general description of the apparent diffusion coefficient dependence for all values of diffusion time has been facilitated by Padé approximant. It has been shown previously several times that the assumption of Gaussian diffusion propagator may not be true for intermediate diffusion times.
This effect is also called diffusion diffraction. Callaghan reported interpretation of diffusion diffractions in beds of spheres by means of pore-hopping model.