Anomalies in supercooled NaCl aqueous solutions: a microscopic perspective

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Supercooled water exhibits unique thermodynamic and dynamic properties distinct from normal liquid water.
• Understanding the influence of solutes, such as salts, on supercooled water is crucial for various scientific disciplines.

Purpose of the Study:

• To investigate the impact of sodium chloride (NaCl) on the thermodynamic and dynamic characteristics of supercooled water.
• To determine how varying salt concentrations affect key properties like isobaric heat capacity and molecular dynamics.

Main Methods:

• Employed molecular dynamic simulations utilizing the TIP5P/E water model and specialized ion parameters.
• Simulations covered a range of NaCl concentrations from 0.19 to 1.33 mol·kg⁻¹.
• Analyzed temperature dependence of isobaric heat capacity (Cp) and other dynamic properties.

Main Results:

• Observed a shift in the maximum of isobaric heat capacity (Cp) to lower temperatures with increasing NaCl concentration.
• Identified characteristic changes around T/T(m) ≈ 0.96, including density minima and a transition in dynamics from Vogel-Tamman-Fulcher to Arrhenius behavior.
• Revealed heterogeneous dynamics at low temperatures, with a common relationship between immobile molecules and T/T(m).

Conclusions:

• NaCl significantly influences the thermodynamic and dynamic behavior of supercooled water.
• The study provides insights into the complex interplay between salt concentration and water's anomalous properties.
• Findings contribute to a deeper understanding of aqueous solutions under supercooled conditions.