Liquid nanofilms. A mechanical model for the disjoining pressure

Liquids in contact with solids are submitted to intermolecular forces making liquids heterogeneous and, in a mechanical model, the stress tensor is not any more spherical as in homogeneous bulks. The aim of this article is to show that a square-gradient functional taking into account the volume liquid free energy corrected with two surface liquid density functionals is a mean field approximation allowing to study structures of very thin liquid nanofilms near plane solid walls. The model determines analytically the concept of disjoining pressure for liquid films of thicknesses of a very few number of nanometers and yields a behavior in good agreement with the shapes of experimental curves carried out by Derjaguin and his successors.