A new study, led by the Universities of Bristol and Tokyo, has concluded that a single, simple factor makes water “so anomalous and special,” and in the process may have solved a longstanding mystery. It may come as a surprise to you that there are still aspects about plain, regular water that elude the world’s greatest minds, but to scientists, this colorless substance is something of a headscratcher.
Water isn’t normal for a liquid. We may think it is because of its apparent ubiquity, but it demonstrates a range of properties that are a little unorthodox. Unlike plenty of other liquids, water has a ludicrously high specific heat capacity, which means it takes a remarkable amount of energy to heat up – something that affects our climate, the environment, and life.
It’s physically quite weird in many other ways. It’s most dense when it’s just 4°C (39.2°F); cooling it makes it expand rather than contract. This means that its solid form floats atop its liquid form, and explains why bodies of water freeze from the top down. This isn’t merely odd; this simple fact of physics also determines a large part of how our planet operates.
As the authors of the new paper, published in the Proceedings of the National Academy of Sciences, put it: “Water is the most common and yet least understood material on Earth.”
Imaging techniques and chemical experimentation has come on leaps and bounds in the last couple of hundred years or so, but water’s properties – not all, but some of them – remain enigmatic. In order to unravel at least a handful, a team of mathematicians enlisted the help of supercomputers, and devised new models that could effectively unwrap the individual molecular and atomic interactions within water.
Just a few years ago, it was confirmed by another research group that water obeys a tetrahedral model. Every molecule of water forms a strong hydrogen bond with four adjacent molecules. In fact, the reason that water has such a high specific heat capacity is because it takes a lot of energy to break these hydrogen bonds in the first place.
In any case, this isn’t the only liquid to possess this arrangement, but the team from Bristol and Tokyo suspected this may help explain why water is so bonkers. Their computational models appear to show that this is correct.
Everything is influenced by a potential parameter of water (and other liquids) known as “lambda,” which controls the degree to which these tetrahedral structures are present. By fiddling with this value, major property changes can appear, disappear, and ultimately be explained.
When the tetrahedrality is low, for example, you get “simple liquid behavior”, according to the study; when it’s higher, you get more energetically stable tetrahedral arrangements, but you also generate a “rich interplay of anomalies.”
Water appears to have a somewhat ideal lambda value, which allows it to switch between states of randomness and order very easily. According to the team, this can “rationalize all of the observations of both thermodynamic and dynamic behavior,” meaning that the chemical and physical oddities of water are all related to tetrahedral changes.
The team has uncovered the one factor to rule them all, a simple explanation for so much complexity, on Earth and beyond. Plenty of mystery remains, however.
“I don't know if this is good news or not, but there is still a lot we don't understand,” lead author Dr John Russo, an applied mathematician at the University of Bristol, told IFLScience. “Crystallization phenomena, solvation effects, glass-forming ability, nanoconfinement… the list goes on.”
