Understanding the impact of ammonium ion substitutions on heterogeneous ice nucleation

Understanding the mechanisms underpinning heterogeneous ice nucleation in the presence of ionic inclusions is important for fields such as cryopreservation and for improved models of climate and weather prediction. Feldspar and ammonium are both present in significant quantities in the atmosphere, a...

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Bibliographic Details
Published in:Faraday discussions 2024-02, Vol.249, p.114-132
Main Authors: Blow, Katarina E, Whale, Thomas F, Quigley, David, Sosso, Gabriele C
Format: Article
Language:English
Subjects:
Algorithms
Atmospheric models
Climate models
Enthalpy
Entropy
Enumeration
Hydrogen bonds
Inclusions
Nucleation
Surface charge
Weather forecasting
Whales
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Summary:Understanding the mechanisms underpinning heterogeneous ice nucleation in the presence of ionic inclusions is important for fields such as cryopreservation and for improved models of climate and weather prediction. Feldspar and ammonium are both present in significant quantities in the atmosphere, and experimental evidence has shown that feldspar can nucleate ice from ammonium-containing solutions at temperatures warmer than water alone. In recent work, Whale hypothesised that this increase in nucleation temperature is due to an increase in configurational entropy when an ammonium ion is included in the ice hydrogen bond network (T. F. Whale, J. Chem. Phys. , 2022, 156 , 144503). In this work, we investigate the impact of the inclusion of an ammonium ion on the hydrogen bond network by direct enumeration of the number of structures found using Rick's algorithm. We also determine the energy of these systems and thus compare the effects of enthalpy and entropy to test Whale's hypothesis. We find that the inclusion of an ammonium ion increases the total number of configurations under conditions consistent with a realistic surface charge. We also find that the enthalpic contribution is dominant in determining the location of the ammonium ion within the structure, although we note that this neglects other practicalities of ice nucleation. We investigate the changes in enthalpy and configurational entropy under the insertion of an ammonium ion into ice. For a reasonable surface charge the most energetically stable configuration of ammonium in ice increases the configurational entropy.
ISSN:1359-6640
1364-5498
DOI:10.1039/d3fd00097d