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!
Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences