FE-CLIP: A tool for the calculation of the solid–liquid interfacial free energy

Abstract

In manufacturing industries, predicting the work of adhesion between complex solid and liquid surfaces has become essential. FE-CLIP offers a routine for evaluating the work of adhesion between solid and liquid surfaces by calling a subroutine from a molecular dynamics simulation code. When FE-CLIP is applied to the solid–liquid interface, liquid molecules are separated from the solid surface according to its shape using a set of spherical potentials. This is efficient when applied to the solid surfaces with complex structures such as polymer-grafted surfaces. An adaptive scheme for updating the parameters contained in the potential and automatic refinement of integration points are introduced to facilitate the application of FE-CLIP to various solid–liquid interfaces. We applied FE-CLIP to the separation of water from a polymer-grafted gold surface to demonstrate that the proposed method gives reliable results by suppressing the variation of the free energy gradient, which is important for accurate numerical integration. Program summaryProgram Title: FE-CLIPProgram Files doi:http://dx.doi.org/10.17632/7gmcvftfwj.1Licensing provisions: GPLv3Programming language: FortranNature of problem: The adhesion free energy of liquid–solid interfaces is one of the important properties for their industrial application. FE-CLIP enables quantitative evaluation of the strength of adhesion between solid and liquid surfaces using a molecular dynamics simulation. Unlike other existing methods, FE-CLIP is efficiently applicable to complex solid surfaces such as polymer-grafted surfaces.Solution method: The work of adhesion between solid and liquid surfaces is calculated using thermodynamic integration. The integration parameters of thermodynamic integration are the diameter and depth of artificial potentials of the Lennard-Jones-type, whose variation contributes to separating the liquid molecules from a solid surface. By putting a set of spherical potentials, the liquid on the solid surface is separated according to the surface shape. In addition, the parameters of the potentials are automatically updated so as to suppress the variation of the free energy gradient.