Kinetic model for molecular transport of liquid mixtures in the vicinity of solid-liquid interfaces

In order to establish a kinetic model that describes the dynamic behavior of liquid molecules moving across liquid-solid surfaces, simple systems consisting of the solid wall and liquid mixtures were applied. Using these systems, MD simulation was performed in which molecular transport associated with adsorption and desorption of liquid molecules onto the solid surfaces were analyzed. In the vicinity of the solid-liquid interface, the density distributions exhibit well-known multiple peaks, which indicates adsorption layers are formed due to solid-liquid interaction. In our model, the molecular transport among the adsorption layers perpendicular to the walls is considered as a kinetic process mediated by molecular hopping which surmounts a free energy barrier between the layers. In this model, the mobility of molecules is expressed as a reaction rate constant of this kinetic process, and then the theoretical relation holds between the height of the barrier and the reaction rate constant. The validity of the kinetic model, which describes the relationship between obtained reaction constants and measured free energy barrier, was examined, comparing the molecular transport observed by MD simulations for liquid mixtures with various molar fractions. A good agreement was found between the theoretical relationships and the observations in the MD simulation.