A diffusive anomaly of water in aqueous sodium chloride solutions at low temperatures.
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.
Kim
Jun Soo
JS
Department of Chemistry and Theoretical Chemistry Institute, University of Wisconsin, Madison, WI 53706, USA.
Yethiraj
Arun
A
D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004058:Diffusion; D005615:Freezing; D012965:Sodium Chloride / Q000737:chemistry*; D012996:Solutions; D013696:Temperature; D014867:Water / Q000737:chemistry*
D012996:Solutions; D014867:Water; D012965:Sodium Chloride