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Is It Possible to Follow the Structural Evolution of Water in "No-Man's Land" Using a Pulsed-Heating Procedure?
Ingrid de Almeida Ribeiro1,2, Maurice de Koning1,3, Valeria Molinero2
1Instituto de Física "Gleb Wataghin", Universidade Estadual de Campinas, UNICAMP, 13083-859 Campinas, São Paulo, Brazil.
The Journal of Physical Chemistry Letters
|January 26, 2022
Summary
Pulsed heating experiments suggest a different temperature for water
Area of Science:
- Physical Chemistry
- Materials Science
- Thermodynamics
Background:
- Supercooled water exhibits anomalous increases in compressibility and heat capacity.
- These anomalies are linked to a structural transformation into a four-coordinated liquid.
- Experimental studies indicate thermodynamic transitions around 229 K, but pulsed heating experiments suggest a lower transition temperature.
Purpose of the Study:
- To investigate the discrepancy between thermodynamic and pulsed heating experimental results for supercooled water.
- To determine if water's structure and thermodynamics are decoupled or if pulsed heating introduces artifacts.
- To clarify the temperature at which water's inherent structure is sampled.
Main Methods:
- Molecular simulations were employed to implement the pulsed heating procedure (PHP).
- Analysis focused on stationary states captured at the bottom of the heating pulse.
- Temperature-dependent distortions were analyzed to understand their effect on transition temperatures.
Main Results:
- Stationary states in pulsed heating simulations do not represent the true thermalized liquid or its inherent structure.
- A temperature-dependent distortion was identified, shifting the observed transition temperature (T_W^PHP) approximately 20 K below the thermodynamic transition temperature (T_W^thermo).
- The study highlights that pulsed heating procedures may not accurately capture the inherent structure of water under current experimental rates.
Conclusions:
- The discrepancy in transition temperatures arises from temperature-dependent distortions during pulsed heating, not decoupled water structure and thermodynamics.
- Pulsed heating procedures require significantly faster rates (2 orders of magnitude) to accurately sample the inherent structure of supercooled water.
- Current pulsed heating methods may lead to artifacts that misrepresent water's structural transitions.
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