Influence of additives on capillary absorption of aqueous solutions into asymmetric porous ceramic substrate

The mechanisms of absorption of water-based solutions of polyelectrolyte (Na-PMAA) or binder (polyvinylalcohol, PVA) into asymmetric porous compacts were studied. The capillary pressure of each solution was calculated from the absorption rate. An absorption model developed for the two-layered structure was used to correlate the solution properties with the absorption dynamics. Na-PMAA increased the capillary pressure in the pores of the substrate. The influence of the surface on the capillary pressure could be explained by the Laplace equation and the Young equation. Na-PMAA decreases the surface tension and improves the wetting of pore walls according to the Young equation. The addition of PVA decreased the surface without an effect on wetting angle, resulting in lower capillary pressures. The absorption of PVA on the pore walls from the advancing liquid meniscus is probably rather slow and therefore the Young equation is not valid. © 2001 Academic Press.