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Quantifying Hofmeister Effects on Polymer-Water Interactions through Freezing Point Depression
Ingrid Eklundh Sørensen1, Esben Thormann1
1Technical University of Denmark, Kemitorvet 206, Lyngby 2800 Kgs, Denmark.
Langmuir : the ACS Journal of Surfaces and Colloids
|February 19, 2026
Summary
Specific ion hydration significantly impacts the freezing point of salt-polymer-water mixtures. Strong ion hydration causes synergistic freezing point depression, unlike weak hydration which shows additive effects.
Area of Science:
- Physical Chemistry
- Polymer Science
- Solution Thermodynamics
Background:
- Understanding freezing point depression in complex solutions is crucial for various applications.
- The Hofmeister series describes ion-specific effects on protein and polymer solubility.
- Polymer-solvent interactions are modulated by dissolved salts, influencing macroscopic properties.
Purpose of the Study:
- To investigate the freezing point depression of ternary salt-polymer-water mixtures.
- To elucidate the role of specific ion hydration in modulating polymer-solvent interactions.
- To establish a thermodynamic framework linking molecular hydration to bulk phase transitions.
Main Methods:
- Utilized poly(ethylene glycol) (PEG) as a model hydrophilic polymer.
- Examined four sodium salts (NaF, NaCl, NaI, NaSCN) representing different hydration strengths.
- Applied the Flory-Huggins equation to analyze freezing point data.
Main Results:
- Freezing point depression of PEG solutions followed the Flory-Huggins equation and was independent of molecular weight (>1000 g mol⁻¹).
- NaF, NaCl, and NaI exhibited synergistic freezing point depression due to strong ion hydration.
- NaSCN showed a nearly additive response, indicating weak hydration and direct PEG association.
Conclusions:
- Ion hydration strength quantitatively correlates with freezing behavior in ternary mixtures.
- A thermodynamic framework was established linking molecular ion hydration to bulk phase transitions.
- Ion-specific effects significantly alter freezing point depression beyond simple colligative behavior.
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