The air-water interface represents a complex chemical system that continues to be actively investigated. Previous research has established that large, polarizable ions, like Br– and I–, are present at the aqueous liquid-vapor interface, but the microscopic origin of this preference is still an open question, particularly as it relates to thermodynamic driving forces. Using molecular simulations with alchemical ion models, we determined that differences in ion size alone are sufficient to cause larger anions to become enriched near the Gibbs dividing surface. Here, we extend that study to explore the effects of temperature. For five temperatures between 284 K and 347 K, we use configurational-bias Monte Carlo simulations in the Gibbs ensemble to determine the spatial distribution of electrolyte mixtures that again differ only in the size of the anions. Water is modeled with the non-polarizable TIP4P model, and special models are used for the ions that vary only in their Lennard-Jones σ parameter. Simulation analysis includes both structural properties—interfacial width, pair correlation functions, hydrogen bonding patterns—and thermodynamic properties—surface tension, Gibbs free energies of transfer between the bulk and the surface of the liquid phase, and van’t Hoff plots.

Spatial distribution of mixtures of electrolytes at the air-water interface for varying temperatures

255th National Meeting (2018)

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