Theory of electrolytes including steric, attractive, and hydration interactions

What is it about?

We have developed a continuum theory for electrolyte solutions, taking into account steric and hydration interactions among the solvent and ions. We regard the solvent as a nearly incompressible fluid, which gives rise to solvent-mediated interactions between ions. Using Boublik-Mansoori-Carnahan-Starling-Leland model for the steric effect and Born model for the hydration effect, we confirmed that our theory successfully reproduces the overall trend of the ion-size-dependence of the effective ion-ion interactions (Collins' rule), activity coefficient, osmotic coefficient, and partial salt volume.

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Photo by Joanna Kosinska on Unsplash

Photo by Joanna Kosinska on Unsplash

Why is it important?

In a system containing ions, ion-specificity arises in various situations such as surface tension, viscosity, and salting-out/in proteins. Here, ion-specificity means that ions having the same valence number cause different effects.There have been a great number of researches to investigate the physical mechanism of ion-specificity, but it still has not well understood even for a basic thermodynamic quantities such as activity coefficient. Hence it is worth developing a simple theory that captures the ion-specificity in thermodynamics of electrolytes. Our theory is potentially applied to more complex situations such as air-liquid interface, hydrodynamics, and soft matters.