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The internet is full of videos like this showing water bottles for drinking used to supercool water. These bottles, not unexpectedly, appear a bit finicky, since they have lots of edges to serve as nucleation sites for ice crystals. What container would work best for this sort of demonstration?

Is the most important quality just to eliminate edges or does the material have an important effect? It's important in lab to add boiling stones as nucleation sites when boiling water in glassware. Could I use this trait for freezing too? Is the important quality of the glass the high surface energy or the smoothness of the surface? Alternatively, it seems like something like PTFE coating with super low surface energy might be effective?

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  • $\begingroup$ Boiling stones has nothing to do with edges: they generate bubbles from the gas absorbed/stored in their pores. Also, most PET bottles has no edges, so it is not a particularly difficult condition to overcome. $\endgroup$ – Greg Aug 6 '15 at 21:43
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    $\begingroup$ Boiling stones most definitely do rely on having abrupt discontinuities... it would be in violation of conservation of matter if the "trapped gas" continually bubbled up as long as liquid were added. $\endgroup$ – DrMoishe Pippik Aug 7 '15 at 5:21
  • $\begingroup$ Frankly I be inclined to use a bottle of soda under pressure. I'd explain the cheat, but explain that you wanted the demo to work reliably. It's the rapid freezing that is the really neat part of the demo. $\endgroup$ – MaxW Feb 19 '17 at 1:07
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One way to approach this problem is think about what kind of material would best promote crystallization, or ice-nucleation, and then essentially use a material that does not have those characteristics.

Consider cloud seeding for example. The whole premise of this is that there is a dearth of ice-freezing-nuclei in the atmosphere, so in the presence of supercooled water droplets, you introduce a compound with a similar crystal structure to ice, like silver iodide for example. Even crystalline compounds with different structures like sodium chloride and dry ice are also effective. So, since we're trying to do the opposite of ice-nucleation, we want opposite characteristics of the surfaces in contact with the supercooled water; nothing crystal-like in nature, something as smooth and clean as possible on a very small scale.

Teflon is a highly hydrophobic synthetic polymer, meaning it's similarity to both liquid and solid water is minimal. A smooth, clean, unscratched Teflon surface is probably the ideal choice. A cheaper option using the same concept would be other organic polymers like polyethylene (probably what the bottles in your video link were made of), polypropylene, HDPE, etc.

Another option that is not crystal-like by definition is any type of consumer glass container. Again, any nano-scale defects or contamination will degrade it's ability to inhibit ice formation from supercooled water.

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  • $\begingroup$ Well I think the point is to see that the liquid hasn't frozen. So the choice has to be transparent which leaves out Teflon. $\endgroup$ – MaxW Feb 19 '17 at 0:44
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    $\begingroup$ @MaxW, yea, I lost track of that a bit with Teflon as my top recommendation, though there are glass containers with a thin layer of Teflon (still expensive and would look like freezing milk at best ;) Something like a brand new 20 mL scintilation vial would probably be ideal, though I partly say that because that's something I always had access to for my demos. I also had the advantage of having tert-butyl alcohol available (MP 25C, supercools nicely). But it worked well with water too, pretty much only if brand new though...just the micro scratches from washing killed them for that purpose. $\endgroup$ – airhuff Feb 19 '17 at 0:57

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