“If you confine a fluid to a nanocavity, you can distort its phase behaviour,” said Professor Michael Strano. In one of the team’s tests, water solidified at 105°C. “The effect is much greater than anyone had anticipated.”
Water’s behaviour changes according to the diameter of the nanotubes – even nanotubes of diameter 1.05nm and 1.06nm saw a difference of tens of degrees in the apparent freezing point.
The team can detect not only the presence of water in the nanotube, but also its phase. According to Prof Strano: “We can tell if it’s vapour or liquid and we can tell if it’s in a stiff phase.” However, the team says it avoids calling it ‘ice’ because that implies a certain kind of crystalline structure. “It’s not necessarily ice, but it’s an ice like phase,” Prof Strano added.
If water can be shown to remain stable indefinitely at room temperature, it could have a range of applications. For example, it should be possible to make ‘ice wires’ that would be among the best carriers known for protons.
However, the researchers admit surprise that water can even enter the nanotubes. Prof Strano explained: “Carbon nanotubes are thought to be hydrophobic, or water repelling, so water molecules should have a hard time getting inside. The fact that they do gain entry remains a bit of a mystery.”