Structure of hard-core Yukawa fluid mixtures near a semi-permeable membrane: A density functional study

The density profiles of binary attractive and binary repulsive hard-core Yukawa (HCY) fluid mixtures with the screening factor λ = 1.8 near a semi-permeable membrane have been investigated using a free energy density functional theory (DFT). The weighted-density approximation of Kierlik and Rosinberg was employed for the hard-sphere term and the mean-field approximation was employed for the long-range dispersion one. Furthermore, a corrected form in the dispersion term was applied to improve the original DFT approach. Extensive comparisons between the theoretical predictions and the grand canonical ensemble Monte Carlo simulation results lead to the conclusion that the original DFT is unreliable to describe the density profiles for binary attractive HCY mixtures near the membrane. In contrast with the original one, the corrected DFT satisfactorily predicts the density profiles for most cases investigated. For the binary repulsive HCY mixtures, both the original and the corrected DFTs provide a relatively better description of the density profiles. The effect of fluid density, temperature, composition and diameter ratio on the fluid structure as well as the osmotic pressure across the membrane has been discussed.