Water can freeze even at high temperatures inside tiny carbon nanotubes, say MIT scientists

Ice-filled wires could soon power electrical devices, MIT scientists that include one of Indian origin named Kumar Varoon Agrawal have said. The scientists have discovered that water has the ability to freeze solid even at high temperatures when inside tiny carbon nanotubes.

Water begins boiling when it reaches at a temperature of 100 degrees Celsius. It is a long known fact that the boiling and freezing points of water can change when it is confined in very small spaces. It usually drops by around 10 degrees Celsius.

Water can freeze even at high temperatures, Scientists from Massachusetts Institute of Technology in the US have found. This would normally set it boiling in carbon nanotubes the inner dimensions of which are not much bigger than a few water molecules.

The discovery reveals that even very familiar materials can drastically change their state when kept inside structures that are measured in nanometres, or billionths of a metre.

The discovery may lead to new applications. For example the ice-filled wires that take advantage of the unique electrical and thermal properties of ice while remaining stable at room temperature.

"If you confine a fluid to a nanocavity, you can actually distort its phase behaviour," said Michael Strano, professor at MIT, referring to how and when the substance changes between solid, liquid and gas phases.

Though these effects were expected, but the enormous magnitude of the change, and its direction (raising rather than lowering the freezing point), were a complete surprise.

The water solidified at a temperature of 105 degrees Celsius or more in one of the tests.

The behaviour of the water changes when it is inside the tiny carbon nanotubes - structures the shape of a soda straw, made entirely of carbon atoms but only a few nanometres in diameter - depends crucially on the exact diameter of the tubes.

The nanotubes were left open at both ends, with reservoirs of water at each opening in the experiments.

Even the difference between nanotubes 1.05 nanometres and 1.06 nanometres across made a difference of tens of degrees in the apparent freezing point, the researchers found. Such extreme differences were completely unexpected.

In earlier efforts to understand how water and other fluids would behave when confined to such small spaces, "there were some simulations that showed really contradictory results," he said.

Part of the reason for that is many teams were not able to measure the exact sizes of their carbon nanotubes precisely, not realising that such small differences could produce such different outcomes, he added.

In fact, it's surprising that water even enters into these tiny tubes in the first place, Strano said.

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, he said.

(With inputs from PTI)