Energy absorbancy and freezing-temperature tunability of NaCl solutions during ice formation

Freezing-thawing cycling of salt solutions is ubiquitously important to fields varying from biochemistry to agriculture, climate, and geological engineering. However, understanding the dynamics of energy exchange and freezing-temperature T-N shift during phase transition of the concentrated solutions remains elusive despite intensive investigations since the discovery of Homeister series in 1888. Here we address this issue by focusing on the performance of the hydrogen bond (O:H-O) in the fraction f(s) molecules of the hydrating supersolid phase and in the remaining fraction f(o) molecules of the pristine phase during NaCI solution ice formation. The supersolid formation is related to the effect of ionic polarization that shortens and stiffens the H-O bond, while lengthening and weakening the O:H non-bonding interactions in the hydration cells. The supersolid phase is gel-like, less dense, viscoelastic, and mechanically and thermally stable. We demonstrate that the polarization-weakening of the O:H non-bonding interactions of the supersolid phase reduces the T-N of the solution and that the H-O cooling contraction in the quasisolid (QS) phase of the pristine water absorbs energy during the Liquid-QS-Ice transition of solution. At f(s) = 1, neither T-N nor energy absorption is resolved within the range of 273 +/- 20 K. The least saturation number of molecules is 10 per pair of Na+ and Cl ions. These findings shall help to develop solutions with tunable T-N for practical applications and to understand the mechanism of energy exchange during phase transition in the temperature and time domains. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The formation of the supersolid phase during NaCI solution ice formation is related to the effect of ionic polarization, which shortens and stiffens the H-O bond while weakening the O:H non-bonding interactions. The supersolid phase exhibits gel-like properties, low density, and viscoelasticity, influencing the T-N and energy absorption of the solution.