Repulsive core-soft models for binary aqueous mixtures

A model for aqueous mixtures, consisting of core-softened water together with a soft-core or core-softened solute, is shown to represent a minimal molecular model for hydrophilic aqueous mixtures. In spite of having purely repulsive interactions, this model is able to produce Kirkwood-Buff integrals very similar to that of the real hydrophilic aqueous mixtures. Monte Carlo simulations and integral equation study of this model are in better agreement between them when entropic effects are predominant. It is intriguing that the entropic effect of purely repulsive interactions capture better hydrophilic effects rather than the hydrophobic ones. The interplay between the concentration fluctuations and the intrinsic structural micro-heterogeneity of these systems help clarifying some of these issues.