Quantitative measurements of capillary absorption in thin porous media by the Automatic Scanning Absorptometer

A 1D model based on Darcy's law is proposed to allow quantitative measurements of the penetration depth of water-glycerol-hexanediol mixtures in thin porous media using an Automatic Scanning Absorptometer (ASA). The limitations of this 1D model are discussed with respect to the nozzle dimensions and the liquid penetration depth. The penetration depth scales with liquid (viscosity and surface tension (η, σ)) and media parameters (average pore radius (r)) as predicted by Darcy's law for Al2O3 disks that are inert to the liquid components. The penetration dynamics in PVDF and MCE filter membranes show a deviation from Darcy's law, indicating specific liquid - media interaction with at least one of the liquid components. Furthermore a linear time regime is observed in the early stages of liquid penetration for time scales much larger than for which inertia effects are expected. This can on the one hand indicate that either, the liquid does not move into the fibrous samples as a homogenous liquid, or that the porous material deforms during the liquid imbibition process. On the other hand, it could be an effect resulting from the complexity of the porous structure itself and an indication of surface film flow formation.