As the bubble freezes, crystals known as the “snowball effect” appear, grow larger and solidify the surface.
When a drop of water or puddle freezes, freezing begins at the coldest point then spreads to the rest. But when it comes to freezing soap bubbles in a low-temperature room, that order is completely disrupted.
Bubbles start to solidify from bottom to top, but then hundreds of thin layers of ice will appear suddenly on the surface. “It’s like the crystals you see in toy snowballs.” That’s why we call this the “snowball effect,” said Jonathan Boreyko, co-author of the study published in the journal Nature Communications.
The “snowball” effect is the result of internal and upward displacement of material flows, due to differences in surface tension. (Photo: The Verge).
Boreyko is a mechanical engineer who runs a lab at Virginia Tech that studies the behavior of fluids, including the behavior of water when it freezes. Boreyko says the new study is based on videos of bubbles on YouTube.
Research results show that the snowball effect occurs due to the Marangoni effect (the movement of matter above or inside a fluid layer due to the difference in surface tension).
Basically, the liquid will flow from a hot place to a colder place. As the bubble freezes in the refrigerator, its liquid part continues to move, ripping ice crystals off the thin ice and moving around. Each of those ice crystals creates their own thin layer of ice, causing the bubble’s surface to solidify faster.
Bubble freezing process, can see the sudden appearance of snow particles concurrent with freezing from the bottom up. (Photo: The Verge).
But in a freezer where everything is the same temperature, how does the bubble have the amount of heat to create a flow? “The answer lies in the freezing itself,” says Boreyko. “It seems absurd, but when you freeze water, it warms itself .”
Boreyko’s group of students tried something a little different, they did it in the lab, and the results were truly different.
Instead of freezing completely, the bottom half of the bubble forms a thin layer of ice and stops.
The warm air in the room holds the bubble in that state until the air begins to slowly escape from the tiny holes in the thin ice. The holes are so small that it takes several minutes for it to completely collapse.
Both experiments yielded intuitive results. If you live in a cold climate, you will have the opportunity to do this experiment in the winter. Just a little soapy solution, a cold surface (like snow) and an air temperature below freezing.
“Anyone can try and that’s part of the reason I did this study,” Boreyko said.
The video below is less than half a minute long documenting the freezing process of the bubble, as beautiful as it was cut out of a fairy tale movie.
Who would have thought that a natural phenomenon lasting only a few tens of seconds could be so beautiful. The way the bubbles gently rotate, the snowflakes gradually cover the surface and turn the recently transparent round block into an opaque white, giving viewers a feeling of stillness and magic.
In addition, this is also a reminder that winter is only beautiful when watching videos in a warm room, not outside where the bitter cold freezes you in an instant.