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Name: Dave
Status: other
Age: other
Location: KY
Country: N/A
Date: 12/22/2004


Question:
How are bubbles frozen?


Replies:
I am not familiar with bubbles "freezing" in the usual sense of the term, that is, freezing the water to form ice. The change in volume upon freezing will undoubtedly rupture the wall of the bubble, and the surfactant necessary to form the bubble initially will separate. It is possible to make the "skin" of the bubble tough with certain polymers such as polyvinyl alcohol so that they do not "pop" when they touch the ground, but this is not "freezing" in the usual sense of the term. If you could provide more specifics maybe we could follow up on the question.

Vince Calder


I presume you mean air bubbles in ice, not soap-bubbles in air, or aircraft instrument attitude indicators. Of course, it is not the air that makes up the bubble that freezes, it is the water around it. Then there has to be some scenario that holds the bubble in the middle of that water long enough for the water to freeze. That's probably done most often by freezing the water on top first, then a bubble happens to rise and bump into this "ice cap", and is stuck there until freezing is complete. It is possible that some air will be forced out of the water by freezing, forming small bubbles where there were none before.

A large bubble that floats up against the underside of an ice sheet will flatten out horizontally. It will not be very spherical. So round bubbles should usually be small ones, roughly 1/8 inch across or smaller. Check that against your experience.

I suppose in glaciers, (ice frozen for a very long time and often at temperatures above -10C, so the ice can slowly flow and air can diffuse through it), small air bubbles could form before or after freezing and eventually grow large, and be spherical. Snow many small air pockets between the flakes, which is trapped when the snow is packed to make glacier ice. Due to the surface energy of the ice (just like surface tension of water), in the long run all this trapped air will try to form a few large bubbles instead of many small ones. If the ice is warm enough and the time is long enough it can do this by individual air molecules diffusing straight through solid ice.

Jim Swenson



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