Electrostatic interaction of charged surfaces with semipermeable membranes

We have investigated the ion density distribution and electrostatic disjoining pressure of the size-asymmetric electrolytes in the gap between the semipermeable membranes and the charged surface by using the density functional theory. The present theory is in reasonably good agreement with the simulation data whereas the Poisson-Boltzmann equation does not describe the electrostatic properties of the electrolytes near a charged surface. The ion density distribution and the electrostatic disjoining pressure depend strongly on the size-asymmetric electrolytes in charge and size as well as the ion density of the electrolyte. The finite size of the ions leads to a large repulsive electrostatic disjoining pressure in the gap. However, the effect of the gap width on the repulsive electrostatic disjoining pressure is very small. The repulsive electrostatic disjoining pressure increases with increasing or decreasing surface charge density with its having a minimum value near a neutral surface. The surface charge amplification and the charge reversal phenomenon are observed for a neutral semipermeable membrane with a charged surface. A positively charged surface enhances the charge surface amplification whereas a negatively charged surface enhances the charge reversal phenomenon.