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Ion Dissociation Dynamics in an Aqueous Premelting Layer.
Samuel P Niblett1, David T Limmer2,3,4
1Materials Science Division, Lawrence Berkeley Laboratory, Berkeley, California 94720, United States.
The Journal of Physical Chemistry. B
|February 22, 2021
Summary
Sodium chloride ions in ice premelting layers exhibit unique dynamics and solvation. Their presence influences interfacial structure and ion pair dissociation rates, differing significantly from bulk water behavior.
Area of Science:
- Physical Chemistry
- Materials Science
- Chemical Physics
Background:
- Aqueous premelting layers form at the ice-vapor interface.
- Understanding solute behavior in these interfacial layers is crucial for various physical and chemical processes.
Purpose of the Study:
- To investigate the thermodynamics and dynamics of sodium chloride (NaCl) in the ice premelting layer.
- To characterize the solvation environment and ion behavior within this unique aqueous interface.
Main Methods:
- Molecular dynamics simulations.
- Importance sampling techniques.
Main Results:
- A hierarchy of relaxation time scales was identified, from picoseconds (ionic motion) to nanoseconds (interface fluctuations).
- Ions preferentially reside in the middle of the premelting layer due to interface distortion and restoring forces.
- Ion pair dissociation is thermodynamically favorable but its rate varies significantly within the layer, being depressed compared to bulk values.
- The solvation environment is distinct from bulk water, characterized by slow water reorganization and an intermediate water structure.
Conclusions:
- The premelting layer presents a unique thermodynamic and dynamic environment for solutes like NaCl.
- Interfacial effects significantly alter ion behavior, including solvation and dissociation, compared to bulk solutions.
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