A less commonly known distinction of water, but one of great interest to physical chemists, is its odd behavior at its transition to the glassy phase. The “glassy state” is a sub-state of matter — glassy water and ice, for example, are chemically identical and have the same state (solid), but have a different structure. Put another way, ice is crystalline, whereas glass is, well, chunky. As water makes the transition to its glassy state, it behaves very oddly, a fact that has baffled scientists.
Arizona State University Regents Professor C. Austen Angell has found a vital clue that helps explain water’s bizarre behavior at the glass transition and, along the way, gained important insights into phases of liquid water as well. His research is published in the Feb. 1, 2008 issue of the journal Science.
“We know a lot about glasses that form from ordinary silicates, sugars and metals,” Angell says. “They’re making golf clubs out of glassy metals these days. But how important is the glassy state of water" And what can it tell us about ordinary water, which is such an anomalous liquid"”
Most glassy forms of matter experience a gradual increase in heat capacity — the amount of energy it takes to heat a sample by one degree Kelvin — until a key transition point is reached. At that point (called the “glass temperature”), these materials suddenly up-jump to a new, 100 percent higher, heat capacity zone and change from a solid to very viscous liquid phase — as if a solid brick of cold honey were heated and suddenly became a sticky liquid again. This occurs even in solutions in which water is the chief component.
In pure water, however, something quite different happens. As cold, glassy water is heated, its heat capacity barely changes until about 136 K (-215 F), where it begins to increase slightly. Then, abruptly at 150 K (-190 F), it crystallizes and stops being glassy. Approached from the other direction, supercooling water produces a similarly odd effect: Heat capacity remains constant as the water cools until around 250 K (-10 F), when it begins to increase very rapidly with decreasing temperature.
Angell wanted to know what was transpiring in the “no man’s land” between 150 and 250 K (-190 and -10 F). Where, he wondered, was the “real” glass transition for glassy water"
He solved the problem by looking at the behavior of both supercooled water and “nanoconfined” glassy ice. Nanoconfined water is water that has been squeezed into pores with a diameter of about 20 angstroms, or 20 hundred-millionths of a meter (roughly five times the scale of atoms and chemical bonds). Using the behavior of water in these states and combining it with a hypothetical behavior of bulk water deduced using the laws of thermodynamics, he was able to bracket the possible heat capacity of water in the “no man’s land” and come up with a novel cooperative transition to explain the substance’s odd behavior.
“Water’s heat capacity suddenly goes crazy near this transition and, before we can see what is happening, it crystallizes,” Angell says. “One trick for finding out what is going on in there is to put the water in a confinement — to make it nanoscopic so that it forgets how to crystallize. We see the same behavior but with no data gap.”
According to Angell, water does not behave like the usual glass formers and therefore lacks the characteristic heat-capacity jump (glass transition) to the glassy phase; instead, because of its unusual hydrogen bond network, it behaves as if it is in a crystalline phase, making what is known as an “order-disorder transition.” This sucks out all of the heat capacity at temperatures around 220 K and explains why the glass transition in water (near 136 K) is so undramatic compared to other substances.
It also gave Angell an idea for a new scenario to explain the odd behavior of supercooled water, one that is compatible with observed behavior but does not require a critical point.
“I wanted to find the answer to the puzzle of what was happening in ‘no man’s land,’” Angell says. “And so I worked up from the glassy state and nanoconfinement.”
“In the end, we say, ‘Well that that’s not what bulk water would do — that’s been thrust upon it by making it so tiny,’” he explains. “But nevertheless it’s an important part of the picture and it supports the conclusion that we’ve got a different sort of thermodynamics in water than we have in any of these other molecular glass-forming liquids.”
Skip Derra | EurekAlert!
The balancing act: An enzyme that links endocytosis to membrane recycling
07.12.2016 | National Centre for Biological Sciences
Transforming plant cells from generalists to specialists
07.12.2016 | Duke University
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
07.12.2016 | Health and Medicine
07.12.2016 | Life Sciences
07.12.2016 | Health and Medicine