Transport of water-glycerol mixtures in porous materials studied with NMR imaging

The penetration of water-glycerol mixtures in a porous material is studied by using NMR (Nuclear Magnetic Resonance) measurements in view of understanding and improving water based inks performance on paper. Al2O3 samples are used as well-defined model systems to quantify the penetration of each mixture component. We investigated the dependence of glycerol concentration in water on the penetration speed, and quantify to what extend the mixture separates in the porous material. We visualized water and glycerol as a function of time and link the behavior of this mixture to the rheological properties. Finally, we investigated the effect of pore size on the imbibition behavior. We found that water-glycerol mixtures penetrate the porous material as a single liquid in both 200 nm and 1100 nm porous Al2O3. Furthermore we showed that the imbibition process can be described by a modified version of Washburn’s equation and that the behavior can be scaled with liquid and media parameters to result in one generic curve. This implies that the complex mixture behaves as a homogeneous liquid and the sorption behavior is determined by the average viscosity and surface tension of the mixture.