On the influence of sodium chloride concentration on equilibrium contact angle

We report experimental results on the influence of sodium chloride concentration on the equilibrium contact angle of droplets of NaCl–water in the presence of air on various surfaces, including hydrophilic and hydrophobic glass plates, Plexiglas, RTV and silicon. It is found that the contact angle significantly increases with NaCl concentration on all hydrophilic surfaces. The contact angle variations are small on the tested hydrophobic surfaces. A simple expression deduced from the Young relation is proposed as a rough estimate of the variations of contact angle with salt concentration. These results are discussed in relation with various salt related transport problems in porous media, such as evaporation, salt weathering and soil contamination.