this is winter magic: blow a bubble outside cold enough and windless enough to enjoy a very beautiful scene. On the surface of the soap bubble, many small ice crystals are formed and dispersed on the liquid film, as if someone had shaken a snowball, and these small ice crystals gradually congealed and grew until the whole bubble was frozen.

you may have seen a similar phenomenon before, and I have posted it before this account, but I still have to send it again this time, because recently I found a very beautiful version! Whether it is the movement of small ice crystals on the liquid film or the formation of branched ice crystals, various details are photographed very clearly.

the above motion pictures are all from the video clip "Winter's Magic" shot by Don Komarechka. If possible, it is recommended to take a look at the original video. In the video introduction, the author also explains how these crystal bubbles are filmed, but it is not easy to shoot this. (original video address: https://youtu.be/mLcmeEL2SYs)

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the following is a scientific explanation given by previous researchers:

at the 70th Annual meeting of fluid Dynamics of the American physical Society, researchers from Virginia Tech gave their explanation. They photographed in a freezer of-20 ℃ and observed how soap bubbles attached to the solid surface froze. As a result, like many popular online videos, they also observed icing like snowballs.

according to the video recording, the researchers explained the specific process of this phenomenon:

① first, small ice crystals were produced at the bottom of the bubble near the solid surface.

② solidification will release heat, and neither the thin soap bubble film nor the surrounding air will transfer heat quickly, so the local liquid film temperature of producing small ice crystals becomes a little higher than that of other places.

③ now, the temperature of different parts of the soap bubble film is different, and this will also bring about the difference of surface tension. As a result, the Marangoni effect appears (yes, it again). As a result, with the convection formed on the liquid film, the small ice crystals at the bottom begin to move upward.

as the ④ moves, the small ice crystals fill the bubble film, and the remaining liquid continues to condense on it. Because of the uniform dispersion of small ice crystals in the condensed nuclei, the whole bubble freezes very evenly, so it is easier to remain intact before it is completely frozen.

A schematic diagram:

if you look closely, you can see the flow of the liquid film, and the small ice crystals at the bottom move upward with the liquid film:

by the way, if only the surface temperature of the solid is low enough, and the surrounding environment is unable to maintain the normal temperature of the ice crystals, then the icing of the soap bubble is slowly upward from the bottom, and the bubble may collapse before it freezes completely. The ice crystals are the most beautiful when the ambient temperature is low enough.

the researcher's complete explanation video can be seen here: https://gfm.aps.org/meetings/dfd-2017/59bac426b8ac316d38841e74

by the way, this is also a phenomenon that I have always wanted to try to shoot, but so far it has not been successful _ (: cold "∠) _ (too cold to want to go out). )