Answering a longstanding question—why is the surface of ice wet?

Answering a longstanding question: Why is the surface of ice wet?
Figures illustrating the process in which a QLL, a thin layer of water on ice, transforms to a state of partial wetting. At the start (0.00 seconds), the surface of the ice is completely covered by the QLL. After six seconds, the layer has turned into droplets (Scale bar: 10 μm). Credit: Murata K. et al., PNAS, October 17, 2016

A team of Hokkaido University scientists has unraveled a 150-year-old mystery surrounding the surface melting of ice crystals in subzero environments by using an advanced optical microscope.

"Ice is wet on its surface": Since this phenomenon, called surface melting, was mentioned by British scientist Michael Faraday more than 150 years ago, the question of why water on the surface of ice does not freeze in a subzero environment remained unanswered.

In their search for the underlying mechanism behind surface melting, the team used a special jointly developed with Olympus Corp. to observe how thin water layers, or quasi-liquid layers (QLLs), are born and disappear at various temperatures and vapor pressure levels.

According to the researchers' findings, thin water layers do not homogeneously and completely wet the surface of ice—a discovery that runs contrary to conventional wisdom. QLLs, therefore, are not able to stably exist at equilibrium, and thus vaporize.

Furthermore, the team discovered that QLLs form only when the surface of ice is growing or sublimating, under supersaturated or unsaturated vapor conditions. This finding strongly suggests that QLLs are a metastable transient state formed through vapor growth and sublimation of ice, but are absent at equilibrium.

"Our results contradict the conventional understanding that supports QLL formation at equilibrium," says Ken-ichiro Murata, the study's lead author at Hokkaido University. "However, comparing the energy states between wet surfaces and dry surfaces, it is a corollary consequence that QLLs cannot be maintained at equilibrium. Surface melting plays important roles in various phenomena such as the lubrication on ice, formation of an ozone hole, and generation of electricity in thunderclouds, of which our findings may contribute towards the understanding."

The research is likely to provide a universal framework for understanding surface melting on other crystalline surfaces, too.


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More information: Ken-ichiro Murata et al. Thermodynamic origin of surface melting on ice crystals, Proceedings of the National Academy of Sciences (2016). DOI: 10.1073/pnas.1608888113
Citation: Answering a longstanding question—why is the surface of ice wet? (2016, November 21) retrieved 15 October 2019 from https://phys.org/news/2016-11-longstanding-questionwhy-surface-ice.html
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Nov 21, 2016
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Nov 23, 2016
@zephTROLL
The thermodynamics by itself doesn't explain, why the surface of these materials remains dry and non-slippery
1- making a claim doesn't make it fact

2- your rebuttal of the paper would have to hold equivalent evidence, like the following
With support from in situ observations with our advanced optical microscopy combined with two-beam interferometry, we have demonstrated that the unique shape of P(e) is responsible for the QLL wetting behavior, and it also plays a prominent role in determining the thermodynamic condition for the existence of QLLs
3- if you're not going to read the paper (it's free) why are you positing that it's not factual?

4- if you're basing your argument on physics, where is your peer reviewed refute?

try actually reading the paper - or at least the conclusions
it points that there are still unanswered questions: maybe you should show them how it should be done? [sarc/]

Nov 23, 2016
" Many organic compounds melts at similar temperature, but the surface of their crystals remains dry. The thermodynamics by itself doesn't explain, why the surface of these materials remains dry and non-slippery."
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They are not in disequilibrium with their vapor in the atmosphere. Put them in such conditions, and I predict you will see it.

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