Farzad Ahmadi and Christian Kingett

How frozen soap bubbles create 'snow globes'

Embargoed until: Publicly released:
Hopefully it's not cold enough in your bathroom to test this one out, but when soap bubbles freeze under certain conditions they can create an effect similar to snow globes, where ice crystals swirl around. Scientists wanted to figure out why this happens, so they put soap bubbles on ice and filmed what happened next. When they did their experiment in a walk-in freezer, the freezing started at the bottom of the bubble and produced a phenomenon where ice crystals detached and swirled around the bubble. At room temperature, the bubbles only partially froze before collapsing.

Journal/conference: Nature Communications

DOI: 10.1038/s41467-019-10021-6

Organisation/s: Virginia Tech, USA

Funder: European Union's Horizon 2020 research and innovation program LubISS, Virginia Tech.

Media Release

From: Springer Nature

How soap bubbles freeze

Insights into how soap bubbles freeze and what causes the so-called ‘snow-globe effect’ that can be produced are revealed in a Nature Communications paper this week.

As soap bubbles freeze under certain conditions, a number of growing ice crystals can be seen to swirl around in an effect visually reminiscent of a snow globe. However, the underlying physics of this phenomenon and how soap bubbles freeze has not been studied.

Jonathan Boreyko and colleagues investigated the heat transfer processes that govern the dynamics of freezing soap bubbles. The authors placed bubbles on a chilled, icy surface under different ambient temperatures and filmed the freezing process. They observed that two different freezing mechanisms take place depending on the temperature.

When the surroundings were at the same temperature as the bubble, freezing started from the bottom of the bubble and produced a Marangoni flow (a liquid flow from areas of low surface tension to areas of high surface tension) causing ice crystals to detach from the freezing front and swirl around the bubble like flakes in a snow globe. The bubble then completely froze as the crystals grew and interlocked together. However, when the surroundings were at room temperature, the freeze front slowly propagated upwards and eventually stopped midway up the bubble, owing to poor conduction. The partially frozen bubble then remained in equilibrium before deflating, and the liquid dome collapsed.

The authors suggest the findings will help contribute to a better understanding of heat transfer phenomena.

Attachments:

  • Springer Nature
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    Please link to the article in online versions of your report (the URL will go live after the embargo ends).
  • Springer Nature
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    Video of a bubble freezing on a block of ice held in a walk-in freezer. The video is being played back in real time.
  • Springer Nature
    Web page
    When a bubble is placed on a cold stage in a room temperature environment, it can only partially freeze. This video shows the eventual collapse of the liquid dome due to the air slowly draining through the pores of the icy base.

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  • Image 1
    Image 1

    Time-lapse photography of a bubble freezing on a block of ice held in a walk-in freezer.

    File size: 2.7 MB

    Attribution: Farzad Ahmadi and Christian Kingett.

    Permission category: © - Only use with this story

    Last modified: 19 Jun 2019 1:07am

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  • Image 2
    Image 2

    Photograph of a bubble freezing on a block of ice held in a walk-in freezer.

    File size: 2.3 MB

    Attribution: Farzad Ahmadi and Christian Kingett.

    Permission category: © - Only use with this story

    Last modified: 19 Jun 2019 1:07am

    NOTE: High resolution files can only be downloaded here by registered journalists who are logged in.

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