(ORDO NEWS) — Supercooled water is two liquids in one. This conclusion was reached by American researchers after carrying out the first-ever measurements of liquid water at temperatures well below its normal freezing point. The research results are published in the journal Science.
Despite its extremely widespread occurrence, water as a chemical is still not fully understood. Scientists sometimes call it the most mysterious substance on Earth.
The fact is that water is not like other liquids – when it freezes, it expands and does not contract like everyone else, while its density decreases. Therefore, water ice does not sink but floats on the surface. Water has a high boiling point and is an excellent solvent, therefore, under various conditions, most organic and inorganic substances dissolve in it. Finally, it has a huge surface tension coefficient. Thanks to all these unique properties, water has become the basis of life on Earth.
Water has one more interesting quality – it freezes very “reluctantly”. If other liquids begin to pass into a solid-state gradually, immediately after they pass the freezing point, then the water “resists” to the last. And for the beginning of solidification, it always needs crystallization nuclei – suspended particles of mineral or organic origin.
Researchers from the Pacific Northwest National Laboratory (PNNL) of the US Department of Energy decided to check, if there are no such particles, to what temperature the water will remain liquid.
It is known that water can be present in clouds in the form of supercooled droplets even at very low temperatures, and then, when from above, from higher and colder layers, fine ice dust falls into these clouds, the droplets instantly crystallize and fall to the ground in the form of ice crumbs or hail.
Scientists in the laboratory destroyed a thin ice film with a laser, creating supercooled liquid water, and then using infrared spectroscopy tracked all the smallest stages of its transformations in the temperature range from 135 to 245 kelvin – from minus 138 to minus 28 degrees Celsius.
In the “freeze frames” of phase states, scientists saw that during supercooling, water condenses into a dense liquid phase, which continues to coexist with the usual liquid phase. In this case, the proportion of liquid with a high density decreases rapidly as the temperature rises from 190 to 245 Kelvin.
“We have shown that liquid water at very low temperatures is not only relatively stable but also exists in two structural forms,” co-author Greg Kimmel said in a press release. “The findings help resolve a long-standing controversy about whether deeply supercooled water always crystallizes before it equilibrates. The answer is no.”
The authors were the first to experimentally prove that supercooled water can be in a stable two-phase liquid-liquid state, and the phase ratio varies depending on temperature. Previously, it was believed that during hypothermia, water inevitably turns into a solid-state over time.
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