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Ice crystals
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Posted on 02/04/2010 6:03:59 PM PST by neverdem
As every schoolchild knows, water freezes at 0oC. Or perhaps not. It has been known for centuries that pure water, in the absence of any nucleating surface, can remain in a supercooled liquid state down to temperatures as low as -40oC. Now, researchers in Israel have discovered that supercooled water itself will freeze at different temperatures depending on whether it is in contact with a positively or negatively charged surface.
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Ice crystals
© Thinkstock Images
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However, it has been difficult to study the phenomenon in any detail because conducting surfaces promote nucleation of water in any event. Now, a team led by Igor Lubomirsky at the Weizmann Institute in Rehovot has devised an elegant experiment in which charge can be created on insulating surfaces to probe electrical effects on the freezing point of supercooled water.
The researchers used the pyroelectric material lithium tantalate (LiTO3), which can develop a positive or negative electrical charge depending on temperature, as a surface upon which to study supercooled water droplets.
They found that on a surface with no electric field, the droplets froze at around -12.5oC. On a positively charged surface, however, the freezing point was raised to - 7oC, while if the surface was negatively charged the droplet did not freeze until the temperature reached -18oC.
There are a number of hypotheses for the effect of electric fields on the freezing of supercooled water, Lubomirsky says. 'The most commonly held belief is that an electric field affects orientation of the water molecules because the latter are polar. We do not have a direct proof of that.' However, it was not previously known that positive and negative charges affected nucleation differently and this, Lubomirsky says, was an unexpected finding and the mechanism remains a mystery. 'This is exactly what we are trying to understand now.'
Paul Connolly, who researches the formation of ice crystals in clouds at the University of Manchester in the UK, says that the new work has uncovered what is 'certainly an interesting phenomenon'. Connolly adds that the results 'may prove useful and provide clues in understanding the mechanism by which ice formation could be enhanced in cumulus clouds.'
That second article is interesting.
I always figure when God was making up the rules one was “Solids will be heavier than the liquid form”. Until after the first winter and everything in the northern lakes died. I could see a Far Side cartoon of that with God up at the blackboard adding in “except water”.
Super-cool or what!
So can I still use it to chill my beer?
Ultrapure water can be strange stuff. While we think of water as being an electrical conductor, ultrapure water is a dielectric. If there is nothing dissolved in it, no H+ and OH- ions. Run the stuff through plastic pipe will produce a static charge. The biggest use I have seen is the semiconductor industry, where it is used to rinse wafers after etching on the wet benches.
Now I am afraid to go ice fishing this weekend! LOL
We love it when you talk dirty.
...researchers in Israel have discovered that supercooled water itself will freeze at different temperatures depending on whether it is in contact with a positively or negatively charged surface."Nice, nice, very nice, nice, nice, very nice, so many people in the same device."
Super cooled water, water everywhere, and not one damn ice cube for my drink.
Pure water has a pH of 7, which means that enough water molecules dissociate so that the concentration of hydrogen ions is 1 part in 10 million.
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