Why Ice floats! “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.

Date:   11/15/2019 2:09:29 AM ( 5 y ago)

Why Water Is Weird
What makes water unique among liquids?
Nautilus |

Brian Gallagher

It’s striking that water can illustrate and elucidate a martial arts philosophy while also being, to this day, the “least understood material on Earth,” as researchers reported recently.

One day, frustrated after many hours of meditation and practice, Bruce Lee, still a teenager, went sailing. His martial arts teacher, Yip Man, had been instructing Lee in the art of detachment, a key facet of gung fu. Lee couldn’t let go. “On the sea I thought of all my past training and got mad at myself and punched the water!” he later wrote. “Right then—at that moment—a thought suddenly struck me; was not this water the very essence of gung fu? I struck it but it did not suffer hurt. I then tried to grasp a handful of it but this proved impossible. This water, the softest substance in the world, which could be contained in the smallest jar, only seemed weak. In reality, it could penetrate the hardest substance in the world. That was it! I wanted to be like the nature of water.”

For Lee, the budding martial artist, water embodied an ideal of lithe and effortless strength. He learned this from ancient Chinese philosopher Lao Tzu’s Tao Te Ching and updated it, adding, “When heated to the state of steam it is invisible but has enough power to split the earth itself.” It’s striking that water can illustrate and elucidate a martial arts philosophy while also being, to this day, the “least understood material on Earth,” as researchers reported recently.

Water can appear to be “fine-tuned” for life.

In their study published in early 2018, Hajime Tanaka, John Russo, and Kenji Akahane—all researchers in the Department of Fundamental Engineering at the University of Tokyo, in Japan—tried to tease apart what makes water unique among liquids. It’s 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 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.”

Nautilus asked Richard Saykally, a chemist at U.C. Berkeley, why these peculiarities make the liquid so ripe for scams and fanciful speculations. 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 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.”

You can enjoy the rest of our conversation with Saykally here, in which he says, among other things, whether another form of liquid water is possible.

Brian Gallagher is the editor of Facts So Romantic, the Nautilus blog. Follow him on Twitter @brianga11agher.

 

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