As everyone with at least a basic grasp of science knows, water, at sea level, starts to boil at a temperature of 212 degrees Fahrenheit, or 100 degrees Celsius. When confined in very small spaces, however, its boiling and freezing points have been observed to drop by about 10 °C.
That being said, what would happen if this were to be taken to its logical conclusion, restricting water to as narrow an area as humanly possible? Apparently, it would freeze solid – even if the ambient temperature would set it boiling otherwise.
The fascinating new discovery was made by researchers at MIT who managed to squeeze water in a set on nanotubes with inner dimensions not much bigger than a few water molecules.
The study, recently published in the journal Nature Nanotechnology, was made possible by highly sensitive imaging systems, using a technique called vibrational spectroscopy, that can track the movement of water inside the nanotubes, thereby making its behavior subject to detailed measurement for the first time.
While changes in phase behavior were expected, their enormous magnitude as well as direction (raising rather than lowering the freezing point) were not. In one of the tests, water solidified at a temperature of roughly 105 °C, although given the difficulties in precise measurement, it could have been as high as 150 °C.
“All bets are off when you get really small,” said Michael Strano, a Carbon P. Dubbs Professor in Chemical Engineering at MIT, and a co-author on the study. “It’s really an unexplored space.”
According to Strano, the contradictory results of previous simulations could be chalked up to researchers failing to measure the dimensions of their nanotubes with enough precision. As the new study showed, even tiny differences diameter (say, jumping from 1.05 to 1.06 nanometers across) can shave off tens of degrees from the apparent freezing point.
Strano and his colleagues were also surprised that water even entered into the nanotubes in the first place, as carbon is thought to be hydrophobic or water-repellent. For now, this remains a bit of a mystery.
While water in nanotubes definitely goes solid, the researchers are reluctant to call it ice, as they haven’t yet been able to conclusively prove the existence of the familiar crystalline structure that is characteristic to it. “It’s not necessarily ice, but it’s an ice-like phase,” said Strano.
In the future, this could lead to engineering ice-filled wires, taking advantage of the unique electrical and thermal properties of ice while remaining stable at room temperature.