Density functional theory of adsorption and phase behavior of the Lennard–Jones fluids confined in MCM-41 with a finite thickness

Abstract

The adsorption and phase behavior of the Lennard–Jones (LJ) fluid confined in MCM-41 with a finite thickness were calculated by using density functional theory (DFT). In the DFT calculation, a potential model representing the interaction between a fluid molecule and MCM-41 pore of finite thickness was used, and the Tarazona's recipe of weighted density approximation was adopted. We reported the effect of different variables, including pore size, temperature, potential well depth, pore wall thickness and fluid molecular parameters, on adsorption isotherm of the LJ fluid confined in MCM-41 pore. The capillary condensation, hysteresis loop and layering transition of the confined LJ fluids were also investigated. Based on the calculated grand potential of the system studied, the phase transition point was determined. The competition of capillary condensation and layering transition of a LJ fluid in confined space was observed. When the interaction between fluid molecule and pore wall is weak, the capillary condensation is of dominance, and the layering transition vanishes on desorption isotherm. In the case of reduction of molecular size, the multi-layer adsorption behavior of the confined fluid appears. In short, the calculated results give a good insight into the adsorption and phase behavior of the confined fluid.