Water is weird. Sure, we absolutely need it for life as we know it to exist, but it has some physical properties that go against how liquid is expected to react under certain conditions. At certain temperatures and pressures, there is a “no-man’s land” where these peculiar qualities get a lot stranger. A new study has revealed the molecular structure of water in this strange state for the very first time and could open the door to a wealth of other research with widespread implications. The research was led by Anders Nilsson of the Department of Energy’s SLAC National Accelerator Laboratory and the paper was published in Nature.
While most liquids contract when they freeze, water expands. Not only that, but it becomes less dense as a solid, which allows ice to float. In cold temperatures, the icy shell still permits marine life to exist unharmed in the cold water below. Under certain pressures, purified water can remain a liquid far below the normal freezing point. Between 232-160 Kelvin (-42 to -172 degrees Fahrenheit), water exists in a no-man’s land where scientists really weren’t sure what was happening to water at the molecular level.
This diagram illustrates the rough boundaries of “no man’s land,” a temperature region where supercooled water is difficult to study because of rapid ice formation. Using SLAC’s Linac Coherent Light Source, scientists dipped down to minus 51 degrees Fahrenheit and made the first structural measurements of liquid water in this mysterious region, where water’s unusual properties are amplified. (Greg Stewart/SLAC, Ultrafast Chemical Physics Group/University of Glasgow, Scotland)
The researchers utilized the new x-ray laser of the Linac Coherent Light Source (LCLS), which used beams that were only quadrillionths of a second long, getting the first glimpse of the molecular structure of water in this no-man’s land. As the beams were given in such rapid succession, they could see how the structure changed over time.
“Now, thanks to LCLS, we have finally been able to enter this cold zone that should provide new information about the unique nature of water,” Nilsson said in a press release.
They found that water’s molecular structure in this no-man’s land was much more dynamic than previous theoretical models had indicated. The structure constantly changes, and the speed at which is does is increased as the water becomes colder.
Water molecules, such as the one modeled at left, rapidly move toward a pyramidal structure, right, when supercooled. In a first-of-its-kind experiment at SLAC’s Linac Coherent Light Source X-ray laser, scientists observed this accelerated transformation. (Greg Stewart/SLAC)
“Our dream is to follow these dynamics as far as we can,” Nilsson went on. “Eventually our understanding of what’s happening here in no man’s land will help us fundamentally understand water in all conditions.”
The team’s next steps of the research will hopefully move on to the glassy water phase, below 160 Kelvin (-172 degrees F). They hope to identify the exact point when water’s weird properties become the most pronounced. By better understanding water when it is most peculiar, scientists will be able to better understand it under normal conditions. This information could be useful when studying ocean currents, biological systems, and climate.