Effect of Hydrophobization on Wetting, Drying and Salt Crystallization in Porous Materials

We discuss the major role played by both the wetting properties of the porous material and the boundary conditions on the drying process. For hydrophobic materials, it will be shown how under some circumstances the evaporation rate becomes lower in the presence of an air flow over the surface than without an air flow, which at first sight seems counterintuitive. Furthermore, as hydrophobic treatment can facilitate the formation of liquid pockets, we discuss how entrapped sodium chloride solution can reach a high supersaturation before crystallization, contrary to what is commonly assumed for this salt. A consequence of such a high concentration is the very rapid growth of a single skeletal (Hopper) crystal, which can lead to damage.