Atomistic simulation of ion solvation in water explains surface preference of halides (original) (raw)

Water interacts strongly with ions, but certain halide anions, such as chloride, bromide, and iodide, preferentially position themselves at the air/water interface. This study conducts a quantitative analysis of ion solvation energetics using molecular simulations, revealing that these halides reside near the surface due to favorable water-water interactions when partially desolvated. In contrast, alkali cations remain in the interior due to beneficial ion-water interactions, while fluoride anions are motivated by entropy to prefer the bulk. These insights challenge existing models and suggest a new understanding of surface preferences driven by energetic rather than simplistic ion characteristics.