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Induction of Microstreaming by Nonspherical Bubble Oscillations in an Acoustic Levitation System
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Investigation of Freezing-Induced Anionic Interplay in Acoustically Levitated Artificial Seawater Droplets
Frank Liang1, Souvick Biswas1, Nils W Melbourne1
1Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, United States.
The Journal of Physical Chemistry. A
|December 16, 2025
Summary
Sulfate ions, not bicarbonate, drive structural changes when artificial seawater freezes. This molecular insight into ice formation impacts atmospheric chemistry and aerosol behavior at subzero temperatures.
Area of Science:
- Atmospheric Chemistry
- Physical Chemistry
- Geochemistry
Background:
- Aerosol freezing behavior is critical for atmospheric processes.
- Soluble salts and ions in droplets influence aerosol physical state and lifetime.
- Understanding ionic transformations during freezing is key to atmospheric modeling.
Purpose of the Study:
- Investigate the freezing behavior of artificial seawater droplets.
- Determine the role of sulfate and bicarbonate anions in ice formation.
- Provide molecular-level insights into seawater ice crystal evolution.
Main Methods:
- Utilized a cryogenically cooled acoustic levitation setup for contact-free droplet analysis.
- Employed in situ Raman spectroscopy to monitor ionic speciation during freezing.
- Performed density functional theory calculations to support experimental findings.
Main Results:
- Sulfate anions exhibited symmetry lowering and spectral broadening upon freezing.
- Bicarbonate anions remained largely unchanged at observed concentrations.
- Sulfate was identified as the primary initiator of ionic transformation during ice formation.
Conclusions:
- Sulfate dictates the structural evolution of seawater ice crystals.
- Sulfate-rich ice surfaces may engage in heterogeneous interactions with atmospheric gases.
- Findings offer molecular-level understanding of aerosol freezing relevant to multiphase atmospheric chemistry.
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