LAUSR

We study the impact, on the drying rate, of the presence of suspended elements, such as calcium sulfate ions, in the interstitial fluid of a porous medium. In order to single out this process in the complexity of a porous medium, we study it through drying in a simple capillary exhibiting characteristics such that it reproduces some critical aspects of drying of porous media. Another specificity of our work is that we focus on the evaporation of ionic solution at their solubility limit. We first show that in such a capillary, the drying process varies depending on the wettability characteristics. Typically, the drying rate is much smaller with hydrophobic surfaces because of the air–liquid interface which tends to withdraw inside the medium, while for hydrophilic surfaces there remains a continuous liquid film up to the entrance. Then, it appears that an ionic solution dries slower than a pure liquid, because the crystals formed along the capillary walls tend to induce a dewetting of the capillary entrance, pushing inward the first liquid–air interface from which most of the evaporation occurs. An experiment with a model colloidal suspension further illustrates this mechanism: The accumulation of solid particles along the wall forms a deposit which pushes inward the first liquid–air interface from which evaporation takes place. Finally, we look at the impact, on the drying characteristics, of the presence of different additives in the ionic solution.