Surface phase transitions of a Lennard-Jones fluid in contact with a permeable wall of finite thickness: a density functional approach

Abstract

We study the phase behavior of a Lennard-Jones fluid in contact with a permeable wall of finite thickness. The wall permeability is modelled by a square-well repulsive potential with a finite height of the potential barrier. The external planes of the wall can also provide an attractive field acting on fluid particles. The structure and phase behavior of the fluid are investigated by means of a density functional method. For high repulsive potential barriers and the walls wide enough, the phase behavior of the system mimics that characteristic for a fluid in contact with a single adsorbing surface. In the case of a purely repulsive membrane, exhibiting an intermediate value of the intramembrane potential barrier, we observe the existence of a surface transition similar to the predrying transition. The dependence of this transition on the membrane width and on the height of the repulsive barrier is studied. We also consider the case of a membrane exerting an attractive field on fluid particles located outside the membrane. In such a case we find the prewetting type surface phase transitions.