A team of researchers from the University of Nebraska - Lincoln has discovered a new form of frozen water with a record-low density that sits as just 25 percent, breaking the previous record synthesized by a team of European scientists back in 2014. If the proposed ice can be synthesized, it will mark the 18th known crystalline form of water and the first discovered in the U.S. since before World War II.
"We performed a lot of calculations (focused on) whether this is not just a low-density ice, but perhaps the lowest-density ice to date," Xiao Cheng Zeng, co-author of the study, said in a press release. "A lot of people are interested in predicting a new ice structure beyond the state of the art."
The team used a computational algorithm and molecular simulation in order to pinpoint the precise ranges of extreme pressure and temperature that would allow the freezing of water into their predicted configuration. This specific configuration takes the form of a clathrate, which is a series of water molecules that attach and form an interlocking structure that resembles a cage.
Previous theories pointed to the need for "guest molecules" in these cages in order to maintain their structural integrity, although Zeng and his team found that their clathrate would retain stability even after the removal of these molecules.
The current study's calculations predict that the new ice will only form when the water molecules are placed inside of a closed space and subjected to extremely high, outwardly expanding pressure. For example, at -10 degrees Fahrenheit, the clathrate would need to be subjected to expansion pressure approximately four times greater than the pressure found in the Pacific Ocean's deepest trench.
"Water and ice are forever interesting because they have such relevance to human beings and life," Zeng said. "If you think about it, the low density of natural ice protects the water below it; if it were denser, water would freeze from the bottom up, and no living species could survive. So Mother Nature's combination is just so perfect."
The findings were published in the Feb. 12 issue of Science Advances.