Makoto Tadokoro / Tokyo University of Science
The new state, known as the “pre-merger state,” has eluded direct observations until now.
Water may look boring, but it’s much stranger than it seems.
In a new, recently published in Journal of the American Chemical Societyscientists in Japan demonstrated that, when confined in extremely small spaces, water molecules can behave simultaneously as a solid and as a liquid.
The differences between liquid water and ice that we observe on a macroscopic scale originate at the microscopic level. In ice, molecules are trapped in rigid structures; in water, on the contrary, they move freely, constantly forming and breaking bonds.
In the peculiar state described in the new study, the molecules do a little of both: they remainfixed in one spot, like ice, but rotate quicklyjust as they would in a liquid. This state, known as “pre-fusion state”, has escaped direct observations until now, explains .
“The pre-fusion state involves the fusion of H₂O molecules with incomplete hydrogen bonds, before the completely frozen ice structure begins to melt during heating,” he explains. Makoto Tadokorochemist at Tokyo University of Science and lead author of the study.
“It essentially constitutes a new phase of water, in which frozen layers of H₂O coexist with others in slow movement”, adds the researcher at the university.
Observing this peculiar state required a complex experimental setup.
From then on, the water used was not exactly the same What we use non-everyday: it was “heavy water”in which hydrogen atoms are replaced by deuterium — an isotope of hydrogen that contains an additional neutron in the nucleus.
This “D₂O” was confined in an extremely small space, where exotic behaviors emerge.
The researchers created rod-shaped crystalswith tiny hydrophilic channels of just 1.6 nanometers longthey froze the heavy water inside and then slowly heated it.
Makoto Tadokoro / Tokyo University of Science
Scientists explore the unique structure and behavior of water molecules confined in nanopores using nuclear magnetic resonance spectroscopy. The study revealed a phase observed in water called the pre-melting phase.
Finally, they observed the entire process using solid-state deuterium nuclear magnetic resonance (NMR) spectroscopy. The technique revealed that the molecules formed a hierarchical structure composed of three layerswith different types of movement and interaction in each of them.
The pre-fusion state is most familiar to us in the form of a thin film of water which forms on the surface of ice, even when temperatures are below freezing. However, under extreme confinementthe phenomenon occurs differently than what occurs in macroscopic ice.
It is already known that water shows unusual behavior confined to the nanometric scale: its electrical properties can change; it can become “unfreezable” even at temperatures close to absolute zero; or, conversely, solidify at temperatures at which, under normal conditions, it would be boiling.
“By creating new ice networks, it may be possible store energetic gases such as hydrogen and methane, as well as developing water-based materials such as artificial gas hydrates”, says Tadokoro.
