title: A diffusive anomaly of water in aqueous sodium chloride solutions at low temperatures.
abstract: Molecular dynamics simulations are presented for the self-diffusion coefficient of water in aqueous sodium chloride solutions. At temperatures above the freezing point of pure water, the self-diffusion coefficient is a monotonically decreasing function of salt concentration. Below the freezing point of pure water, however, the self-diffusion coefficient is a non-monotonic function of salt concentration, showing a maximum at approximately one molal salt. This suggests that sodium chloride, which is considered a structure-making salt at room temperature, becomes a structure-breaking salt at low temperatures. A qualitative understanding of this effect can be obtained by considering the effect of ions on the residence time of water molecules near other water molecules. A consideration of the freezing point depression of aqueous sodium chloride solutions suggests that the self-diffusion coefficient of water in supercooled sodium chloride solutions is always higher than that in pure (supercooled) water at the same temperature.
authors.affiliation: Department of Chemistry and Theoretical Chemistry Institute, University of Wisconsin, Madison, WI 53706, USA.
authors.forename: Jun Soo
authors.initials: JS
authors.lastname: Kim
authors.forename: Arun
authors.initials: A
authors.lastname: Yethiraj
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004058:Diffusion; D005615:Freezing; D012965:Sodium Chloride / Q000737:chemistry*; D012996:Solutions; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D012996:Solutions; D014867:Water; D012965:Sodium Chloride