Forces due to solvent structure in fluid mixtures and asymmetric electrolytes

Abstract

A density-functional theory of the free energy of a fluid confined by solid walls is extended to deal with fluid mixtures in which the constituent particles differ in size. In mixtures of electrically neutral particles the solvation force is found to be sum of the forces due to each component, each of which has the characteristic oscillatory form seen in previous studies of single-component fluids. The theory is further extended to treat mixtures of charged particles, and the results for an asymmetric 1:1 electrolyte are given. The asymmetry in the ion size is seen to play an important role in determining the form of the solvation force for electrolyte concentrations ≳0.5 mol dm^–3.