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Formation of ice requires a phase change. Generally this
occurs easiest through heterogeneous transformations, ie it
nucleates on a particle or surface. The wetting angle the
water experiences at the solid/liquid interface drives the
preferential decrease in required energy to nucleate into ice.
Modification
of the surface of roads so that they are very
hard to wet and hence the energy required for nucleation is
higher.
Issues come about with any dirt may allow nucleation barrier
to be dropped again, and I think once some Ice forms then it
would quickly allow the rest of the water to nucleate.
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Annotation:
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This would be worse than the ice. |
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Would the final result be a propensity to remain wet until some
trigger for sudden ice formation in a matter of seconds? |
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This does has some practicality. Ice will still form, but breaking the bond between the road and the snow/ice allows for easier removal. That is basically all road salt does through brine formation. |
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Reducing the wetting angle (ie, making the road
hydrophobic) involves *decreasing* the surface
energy, shirley? Wetting happens because the
road-water interface has less surface energy than
the surface of the road and of the water
independently; raising surface energy of the road
simply makes wetting more favourable. So you
want to *lower* the road's surface energy. |
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Secondly, surface water is full of dust particles,
which are more than adequate to nucleate ice
formation, so a non-wettable surface won't really
affect ice nucleation. |
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Thirdly, wetting releases energy as heat.
Therefore, wetting actually _delays_ ice formation
(very slightly) by warming the surface. |
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So, regrettably, I suspect that this idea has scored
a hat-trick of wrongth. |
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It is my observation that most things that repel water are also slippery. We generally don't need that feature as part of a road surface. At least, not at this time. Perhaps, in the future, when everyone is driving vehicles that require a low-friction road surface.... |
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We went through all of this last winter, didn't we?
Something about a hydrophobic compound mixed with the
asphalt medium, and there was another one about a road
surface with billions of tiny dimples or something, and a
couple of others involving channeled exhaust heat, and
then [AusCan] and I had to explain to everyone what 'rock
ice' is and why it's better to have the icy roads dry rather
than wet... Does any of that sound familiar at all? |
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heterogenous nucleation energy is determined by |
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homogenous nucleation energy * function of
wetting angle |
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function is 1 when wetting angle is 180 degrees |
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a wetting angle of 180 degrees is perfectly non-
wetting |
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That wonderfully scientific description goes way over my
gears 'n' guts head, but if you're suggesting
wetting roads in winter conditions, forget it, my friend.
It's a recipe for disaster at any angle. |
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