The end of ice I.
Daniel R Moberg1, Daniel Becker2, Christoph W Dierking2
1Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA 92093.
Summary
Researchers found that nanoscale water clusters exhibit ice I crystallization around 90 molecules. This transition differs from bulk water, showing heterophasic oscillations instead of a sharp phase change.
Area of Science:
- Physical Chemistry
- Nanoscale Science
- Water Science
Background:
- The crystallization of water into ice I at the nanoscale and its coexistence with liquid water remain poorly understood.
- Previous studies lacked definitive evidence for ice I formation in very small water clusters.
Purpose of the Study:
- To investigate the emergence of ice I structure in small water clusters.
- To characterize the phase behavior and coexistence of liquid water and ice I in nanoscale clusters.
Main Methods:
- Utilized experimental and theoretical infrared spectroscopy.
- Employed free-energy calculations to analyze water cluster behavior.
Main Results:
- Identified the characteristic hydrogen-bonding pattern of ice I in clusters as small as approximately 90 water molecules.
- Observed spectral indicators of nanoscale crystallinity, including increased surface oscillator intensity with decreasing surface-to-volume ratio.
- Found mixtures of crystalline and amorphous clusters in the 90–150 water molecule size range.
Conclusions:
- The liquid-ice I transition in clusters loses its sharp first-order character at the nanoscale.
- This transition occurs over a temperature range via heterophasic oscillations, a phenomenon not seen in bulk water.
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