May 23, 2019 | Updated: 11:35 AM EDT

Water’s Weirdness Explained

May 02, 2019 08:25 AM EDT


Japan - In their 2018 study, researchers from the Department of Fundamental Engineering at the University of Tokyo tried to tease apart what makes water unique among liquids. Hajime Tanaka, John Russo, and Kenji Akahane discovered water got anomalous properties, like expanding when cooled below 40 degrees Fahrenheit, which explains why lakes freeze downward, from top to bottom, rather than up.

Normally frozen solids are denser than their liquid equivalents, which would mean that frozen chunks would fall to the bottom of a lake instead of staying on top. Water also becomes less viscous compared to other liquids when compressed, and has an uncanny level of surface tension, allowing beings to light enough, like insects, to walk or stand atop it. Since it's these distinctive features among others that power our climate and ecosystems, water can appear to be "fine-tuned" for life.

The researchers, with the benefit of supercomputers, were able to tweak and untune a computational model of water, making it behave like other liquids. "With this procedure," Russo said, "we have found that what makes water behave anomalously is the presence of a particular arrangement of the water's molecules, such as the tetrahedral arrangement, where a water molecule is hydrogen-bonded to four molecules located on the vertices of a tetrahedron," a shape of four triangular planes. "Four of such tetrahedral arrangements can organize themselves in such a way that they share a common water molecule at the center without overlapping," Russo said. As a result, when water freezes, it creates an open structure, mostly empty space and less dense than the disordered structure of liquid water, which is why water props ice up. Both highly ordered and disordered tetrahedral arrangements give water its "peculiar properties." The paper's title spells this out: "Water-like anomalies as a function of tetrahedrality."

When asked why these peculiarities make the liquid so ripe for scams and fanciful speculations, Richard Saykally, a chemist at U.C. Berkeley explained that the ancient Greeks thought water was one of the four "essential" elements, the others being earth, air, and fire. Homeopathy, which purports to cure illness using small doses of disease-causing substances dissolved in water, evolved out of this, Saykally said. But there are more modern magical claims about so-called "structured" or "hexagonal" water. Some "wellness" practitioners claim humans age in part because we don't replenish our stock of structured water. Depending on water's structure, they say, it can penetrate your cell walls more effectively and has all kinds of health benefits.

"There's no scientific basis to that at all," Saykally said. "You can't make structured water. Doesn't make any sense because the hydrogen bond in water lives for a few picoseconds-10-12 seconds-and these hydrogen bond structures of water are rearranging very rapidly so you don't have water clusters existing as isolated entities in the water despite a lot of these claims."

The ancient Greeks may have been wrong about water being an essential element, but Saykally says it's no coincidence that water is essential for life on Earth. "It's something intrinsic about water in that the strong tetrahedral hydrogen bond network that water makes is a very flexible environment for chemical processes to happen," he said. "It has the right properties to dissolve many ions; it has the right properties to cause what we call hydrophobic materials-like proteins-to fold up in special ways."

Saykally has invented a new laser to study water clusters, with the ultimate goal of producing "the perfect model for water," he said. "We want to combine all the information available from studies of water clusters with our terahertz laser spectroscopy-from quantum chemical calculations and from condensed phase measurements-and make a computer model of water that will answer any question you ask. That perfect water model is what we have been calling the universal first principles model of water."

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