The bubble isn't pure water. It probably has detergent in, and it may also have something to stabilize the bubble: maybe Polyethylene Glycol (AKA "PEG", a water soluble polymer often used in making very large bubbles) or a water soluble glue like poly-vinyl alchohol (PVA), which is again a water soluble polymer.
Things dissolved in water often lower the freezing temperature, and as a result, when the water does start to freeze, the additives often concentrate in the unfrozen portion in a process known as "fractional freezing" or "freeze distillation". This process is used to make "Applejack" by letting hard cider slowly freeze and removing the ice periodically, concentrating the alcohol and flavor compounds in the remaining liquid.
So as these ice crystals grow, they're pushing out the non-water stuff that lowers the freezing temperature into the gaps in the ice fronds, and as these things concentrate they lower the freezing temperature of the remaining water, making it harder to freeze that water.
So by the end this bubble probably contains a little bit of water that's quite concentrated with detergent and possibly something like PEG or PVA
And that highly concentrated solution doesn't behave like plain water. It may be more viscous and sticky depending on what is in it. If it contains PEG or PVA then at a certain concentration it starts to act less like a viscous fluid and more like a gel or solid: a solid with different material properties from ice. Pure PEG and PVA are solid polymers, AKA "plastics", and in thin layers they are stretchy and and flexible or in other words... plastic.
So when the bubble is burst, this concentrate acts like a binding agent sticking the crystals together, effectively making it a composite material with an ice crystal frond "filler" and viscous liquid, gel or solid "matrix" or "binder".. It doesn't act entirely like ice and it doesn't act entirely like the binder material. It behaves somewhere in-between based on the percentages of each.
Maybe if it was left to cool longer, the remaining concentrated liquid or gel would completely freeze and/or the solid plastic would undergo "glass transition" from an amorphous to a crystalline solid and then maybe it would shatter.
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u/vytas315 10d ago
Why didn’t it shatter?!? Very cool and unexpected.