MIT
researchers have learnt something unexpected about water. Inside really
confined spaces, such as carbon nanotubes, water freezes at
temperatures where it would normally boil. The inner dimensions of these
carbon nanotubes are not more than a few water molecules in diameter.
Ice has unique electrical and thermal properties that can potentially
lead to ice filled wires.
The discovery
shows how even commonplace materials can behave unexpectedly in
extremely confined spaces. The diameter of the nano tubes are critical
for the unique properties of water to be seen. A difference of 10
degrees was observed in the freezing points of water in tubes that were
1.05 nanometers across compared to tubes that were 1.06 nanometers
across. The tubes were tested with water reservoirs on either end.
In previous such efforts to understand the behavior of liquids in
confined places, the results were unpredictable because of the inability
of researchers to measure the inner diameters of nanotubes with
precision. Carbon nanotubes are believed to be hydrophobic, where the
surfaces naturally repel water. It is a mystery how water even gets into
such small nanotubes. The researchers are using highly sensitive
imaging technology called vibrational spectroscopy to study the movement
of the water within the tube, the first time such a detailed
measurement has been undertaken.
While the team has observed a solid ice like stage within the
nanotubes, the researchers are hesitant to call it ice because they have
not yet conclusively proved that the solid material has crystalline
structures seen in ice. The “ice wires” have a potential to be the best
conductive material for protons, because water conducts protons ten
times more readily than conventional conductive materials. The research
is being reported in the journal called
Nature Nanotechnology.
