Evidence of low-density and high-density liquid phases and isochore end point for water confined to carbon nanotube

Research Highlight

Squeezing water

© theasis/E+/Getty

© theasis/E+/Getty

Water could exist in two liquid phases not yet observed at room temperature if squeezed into a carbon nanotube.

As a solid, water can take on at least 21 forms depending on the surrounding temperature and pressure. However, low- and high- density forms of liquid water have so far only been predicted to arise below -43 degrees Celsius, making them hard to detect before the water freezes. An international team including researchers from Keio University modelled what would happen to water under increasing pressure when confined in a carbon tube 1.25 nanometres in diameter. The simulation suggests that, at a constant temperature of 7 degrees Celsius, raising the pressure in the tube from 10 to 600 megapascals turns the water into a low-density liquid before it freezes in a hexagonal ice structure and then melts again into a high-density liquid.

The hexagonal ice phase has already been observed at ambient temperatures in the lab, suggesting that these long-predicted liquid phases could be readily tested for.

Supported content

  1. PNAS 114, 4066–4071 (2017). doi: 10.1073/pnas.1701609114
Institutions FC
Department of Chemistry, UNL, United States of America (USA) 0.42
Department of Mechanical Engineering, Keio University, Japan 0.33
Faculty of Engineering, TUS, Japan 0.08
Research Institute for Science and Technology (RIST), TUS, Japan 0.08
Beijing Advanced Innovation Center for Soft Matter Science and Engineering, BUCT, China 0.08

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