This article comes from WeChat’s personal WeChat account “Cool Science”, which may not be reproduced commercially without permission
This is the magic of winter: blowing a bubble in the cold and windless outdoor can enjoy a very beautiful scene. On the surface of soap bubbles, many small ice crystals are formed and dispersed on the liquid film, as if someone shakes the snow ball. These small ice crystals gradually condense and grow until the entire bubble is frozen.
You may have seen similar phenomena before, and I posted it before this account, but I have to post it again this time, because recently I found a very beautiful version of the shooting effect! Whether it is the movement of small ice crystals on the liquid film or the formation of branched ice crystals, all details are shot very clearly.
The above animations are all from the short video “Winter’s Magic” by Don Komarechka. If possible, it is highly recommended to watch the original video. The author also explained how these crystal clear crystal bubbles were shot in the video introduction, but it is really not easy to shoot this… (original video address: https://youtu.be/mLcmeEL2SYs)
The following is a scientific explanation given by previous researchers on this process:
At the 70th annual meeting of the American Society of Physics for Fluid Dynamics, researchers from Virginia Tech gave their explanations. They photographed in a freezer at -20°C and observed how the soap bubbles attached to the solid surface freeze. As a result, like many popular videos on the Internet, they also observed the phenomenon of freezing like a snow globe.
According to the video recording, the researchers explained the specific process of this phenomenon:
① First, small ice crystals were generated at the bottom of the bubble near the solid surface.
②The solidification will release heat, and neither the thin soap bubble film nor the surrounding air will dissipate heat quickly, so the temperature of the local liquid film that produces small ice crystals becomes a little higher than other places.
③Now, there are differences in the temperature of different parts of the soap bubble film, and this will also bring about differences in surface tension. So, the Marangoni effect appeared (yes, it was again). As a result, with the convection formed on the liquid film, the small ice crystals at the bottom start to move upward.
④ As it moves, the small ice crystals fill the bubble membrane, and the remaining liquid continues to condense on it. Because the small ice crystals of the condensed nodules are evenly dispersed, the entire bubble freezes very evenly, so it is easier to keep it intact before completely freezing.
A schematic diagram:
If you look closely, you can see the flow of the liquid film. 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 cannot maintain the normal temperature of the ice crystals, the icing of the soap bubbles slowly rises from the bottom, and the bubbles may collapse before they are completely iced. The ice crystals formed when the surrounding temperature is low enough are the most beautiful.
The full explanation video of the researcher can be seen here: https://gfm.aps.org/meetings/dfd-2017/59bac426b8ac316d38841e74
By the way, this is also the phenomenon I always wanted to try to take a picture, but it has not been successful so far _(:з」∠)_ (it’s too cold and I don’t want to go out…)
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