The excluded volume effect in confined fluids and liquid mixtures

It is shown that unless excluded volume effects are included in the comparison between solution and pure liquid radial distribution functions, the conclusion that a particular solute either enhances, decreases or has no effect on solvent structure may be erroneous. The effect is most pronounced when the ratio between the volume occupied by the solute molecules or ions and that occupied by the solvent molecules approaches unity. The case of acetylcholine in aqueous solution is analysed as an example.