Understanding the effect of salt concentration on the surface wettability using multiscale simulation

Abstract

The wettability is quite an important property of solid surface in various field. Many researchers interested in hydrophilicity of salt aqueous solution on graphene because the graphene is used as a promising material for desalination. Nevertheless, we still cannot measure the contact angle exactly due to several factors and understand what happens at a solid and liquid interface. The DFT-CES method as a QM/MM is used for describing the work of adhesion as a solid-liquid interface interaction and the 2PT analysis tool is used to obtain difference free energy quantitatively. The partial molar volume is needed to using the 2PT tool to deal with the multi-component liquid and it can be calculated by the Voronoi option of the LAMMPS program. The contact angle can be calculated using the Young-duépre equation with the work of adhesion and surface tension. The work of adhesion is not change compared with the pure water system and the surface tension rises as concentration increases. We can derive the new equation from the results of the simulation to calculate the contact angle between the multi-component liquid and flat surface solid. As a result of the simulation, it can be seen that the characteristics change from hydrophilic to hydrophobic at about 3m. Extending the new equation to non-flat surface solid, we also derive the equation to calculate contact angle between the multi-component liquid and rough surface solid.