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Related Experiment Video
Updated: Jan 23, 2026

In Situ Characterization of Boehmite Particles in Water Using Liquid SEM
Published on: September 27, 2017
Is water one liquid or two?
1ISIS Facility, UKRI-STFC Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire OX11 0QX, United Kingdom.
This study analyzes water's structure, finding density fluctuations are too small for distinct high and low-density states. Water does not exhibit two-phase behavior, challenging existing theories.
Area of Science:
- Physical Chemistry
- Materials Science
- Statistical Mechanics
Background:
- The concept of water existing as a mixture of two distinct states (high-density and low-density) is a topic of ongoing research.
- Understanding water's anomalous properties, such as its negative thermal expansion, is crucial in various scientific fields.
Purpose of the Study:
- To analyze the validity of the two-state model for water.
- To investigate the density fluctuations and entropy of water across different phases and conditions.
- To determine if water exhibits two-phase behavior based on density and entropy distributions.
Main Methods:
- Analysis of water's compressibility and density fluctuations at the nanoscale (1 nm³).
- Utilizing neutron and X-ray scattering data with empirical potential structure refinement simulations.
- Calculating configurational entropy via spherical harmonic reconstruction of orientational pair correlation functions.
Main Results:
- Density fluctuations in water are too small (≈4%) to support significant high- and low-density regions.
- Simulations indicate water is in a one-phase region, not a two-phase region, across explored liquid and amorphous states.
- Entropy calculations show a declining trend with decreasing temperature and do not support distinct high-entropy/low-entropy states coexisting.
Conclusions:
- The hypothesis of water as a mixture of two distinct states is not supported by the analyzed data.
- Water's behavior is better described as a single phase, with density fluctuations insufficient for a clear two-state distinction.
- While temperature influences entropy, high-density water does not possess significantly higher entropy than low-density water at ambient conditions.

