It covers about 70 percent of Earth's surface and comprises roughly 60 percent of our bodies by mass, yet water remains scientifically anomalous.
Like an aqueous Jekyll and Hyde, water crystallizes at low temperatures, taking the familiar form of ice. Or it can become "glassy water", with an amorphous, messy molecular structure.
This weird form of water is found in stratospheric clouds in polar climes. It also helps cold-loving (psychrophilic) organisms prevent ice-crystal-induced cellular damage at bone-chilling temperatures.
Yet water's transformation from liquid to glass has largely remained hidden from observational techniques.
When it freezes, water typically forms ice crystals that lock together in a rigid, orderly structure. This happens at temperatures as low as about -45 degrees Celsius (-49 degrees Fahrenheit) – below which lies a vast, poorly understood thermal wilderness referred to by scientists as "no man's land".
Bulk water's glassy transition was thought to occur somewhere around -135 degrees Celsius, but crystalline ice obscured researchers' attempts to reach this glassy precipice.
In a new study, scientists solved that issue by trapping water in a matrix, inspired by nature's own tricks, and realized they'd been missing water's glassy transformation all along, in the blur of crystallization.
Writing in Nature Communications, physicists locked tiny amounts of water – just a few molecules thick, or less than a billionth of a meter – between two lipid layers made of a special 'transparent' type of phytantriol, a fatty alcohol molecule that remains structurally stable and fluid across chilly thermal regimes.
Thus trapped, the water was prevented from crystallizing as the temperature dropped, allowing the researchers to track its liquid-to-glass transition in impressive detail.
Surprisingly, they found that this glassy transformation emerges over a much larger – and higher – temperature range than previously thought.
To track the behavior of water at sub-nanometer scales, a team of physicists led by Raffaele Mezzenga at ETH Zurich, collaborating with scientists at the Australian Nuclear Science and Technology Organisation (ANSTO), combined computational models with a suite of advanced atomic-probing techniques.
One observational avenue employed ANSTO's Small Angle and Wide Angle X-ray Scattering (SAXS/WAXS) beamline, to map the structure of the water trapped within the lipid matrix at different temperatures, via intensely bright X-rays produced in a synchrotron, or particle accelerator.
The team also employed two spectrometers, named Emu and Pelican, at the Australian Centre for Neutron Scattering to detect molecular vibrations and reveal the motion of hydrogen atoms within the sample.
"The neutron signal, detected by our instrument, is dominated by the motions of hydrogen atoms in water," explains Alice Klapproth, an ANSTO instrument scientist for the Emu spectrometer.
"This allows us to selectively measure water dynamics even when the water is confined within a complex soft matrix."
Altogether, the researchers detected a slowing of the confined water's dynamics occurring over a surprisingly large range, from -63 to -20 degrees Celsius; a shift they explored across six temporal orders of magnitude, from millionths to just trillionths of a second.
Specifically, a dramatic change in molecular dynamics occurs around -35 to -21°C, as the kinetic action of water molecules gets sluggish. And the static glass structural transition occurs between -74 to -64 degrees Celsius, as water becomes locked into a disorganized glassy, solid state.
Then, when the mercury really drops, it starts cracking like an icy alien slab of peanut brittle.
In addition to illuminating the dynamics of an everyday-but-still-enigmatic substance, this research may lead to practical applications.
"More generally and beyond the purely fundamental aspects, our findings bear immediate and broader relevance to all physical phenomena involving cryogenic nanoconfined water, such as in the cryopreservation of biological material and deep freezing of food, to name only a couple of examples," the researchers conclude.
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Whether such applications could, however, lead to improvements in restoring preserved tissues or a revolutionary smooth breed of ice cream remains to be seen.
This research was published in Nature Communications.
This article was fact-checked by Clare Watson and edited by Clare Watson. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.