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Phase separation during freezing upon warming of aqueous solutions
1Institute of Physical Chemistry, University of Innsbruck, Innrain 80/82, A-6020 Innsbruck, Austria.
The Journal of Chemical Physics
|November 17, 2014
Summary
Adding solutes to emulsified water significantly lowers freezing temperatures, suppressing ice formation. Upon warming, phase separation occurs, forming pure ice and concentrated solutions that can vitrify at lower temperatures than pure water.
Area of Science:
- Physical Chemistry
- Materials Science
- Nanotechnology
Background:
- Understanding the phase behavior of water under confinement is crucial for various scientific fields.
- The freezing point depression and glass transition of water are significantly influenced by solutes and confinement effects.
Purpose of the Study:
- To investigate the freezing behavior and phase transitions of emulsified water with solutes using differential scanning calorimetry.
- To compare the properties of water nanodrops on fumed silica with bulk water and confined water.
Main Methods:
- Differential scanning calorimetry (DSC) was employed to study the thermal properties of emulsified water solutions.
- Varying concentrations of solutes, including HCl, were added to emulsified water to observe freezing point depression and glass transition.
Main Results:
- Solutes lowered the freezing temperature of emulsified water below the homogeneous nucleation temperature of pure water (<231 K) or suppressed freezing entirely.
- In cases of suppressed freezing, warming induced phase separation into pure ice and a freeze-concentrated solution (FCS) above ~150 K.
- Emulsified HCl solutions and their FCS vitrified at lower temperatures (127-128 K) compared to pure water (136 K).
Conclusions:
- Water nanodrops adsorbed on fumed silica exhibit properties more akin to bulk water than to water in nanoscaled confinement.
- The presence of solutes significantly alters the freezing and glass transition behavior of emulsified water.
- Phase separation into ice and concentrated solutions is a key phenomenon in suppressed freezing scenarios.
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