Sorption of water-glycerol mixtures in porous Al₂O₃ studied with NMR imaging

The penetration of water-glycerol mixtures in porous Al₂O₃ is measured using NMR imaging to quantitatively describe the liquid penetration and possible front separation of liquids in non-transparent porous media. We have studied the dependency on viscosity over two orders of magnitude by changing the glycerol concentration and have investigated the effect of pore size in the micrometer and sub-micrometer regime. We show that the liquid dynamics can be accurately described by Darcy's law for all investigated liquid – media combinations and show that the permeability scales with the pore radius squared as predicted by permeability models by Lucas-Washburn and Katz-Thompson. Furthermore we have used T₂ relaxation analysis to investigate the homogeneity of the imbibing mixture during uptake and have found that water-glycerol mixtures penetrate the porous Al₂O₃ samples as a single homogeneous liquid.