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

Squeezing water

23 November 2017

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.

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References

1. PNAS 114, 4066–4071 (2017). doi: 10.1073/pnas.1701609114