论文标题：How soap bubbles freeze

期刊：Nature Communications

作者：S. Farzad Ahmadi, Saurabh Nath, Christian M. Kingett, Pengtao Yue, Jonathan B. Boreyko

发表时间：2019/06/18

数字识别码： 10.1038/s41467-019-10021-6

原文链接：http://t.cn/AipA1OnK

微信链接：https://mp.weixin.qq.com/s/JTWZ1Ddv2gBbhhmzsOu9-Q

本周《自然-通讯》发表的一篇论文How soap bubbles freeze揭示了肥皂泡是如何冻结，以及所谓“雪花玻璃球效应”(snow-globe effect)是如何产生的。

图1：冷库内一块冰上的泡泡结冰的过程。图源：Farzad Ahmadi 和Christian Kingett

肥皂泡在特定条件下冻结时，可以观察到内部有大量不断生长的冰晶在盘旋，让人不禁联想到雪花玻璃球。然而在此之前，未有研究调查过这种现象背后的物理机制以及肥皂泡是如何冻结的。

图2：冷库内一块冰上正在结冰的泡泡。图源：Farzad Ahmadi 和Christian Kingett

美国弗吉尼亚理工学院的Jonathan Boreyko及同事研究了主导肥皂泡冻结的热传递过程。他们在不同环境温度下，将肥皂泡置于冰冷的表面，并记录下了冻结过程。他们观察到了两种不同的冻结机制，具体视温度而定。

视频：一块冰上正在结冰的泡泡。来源：Farzad Ahmadi 和Christian Kingett（请到微信观看视频）

当周围温度与肥皂泡温度一样时，冻结从肥皂泡底部开始，并会产生马拉高尼流（液体从表面张力低的地方流向表面张力高的地方），导致冰晶脱离冻结界面，并在肥皂泡周围旋转，就像雪花玻璃球里面的雪花一样。之后，随着冰晶不断生长和并合，肥皂泡完全冻结。但是，当周围温度为室温时，冻结界面会缓慢向上扩展，最终在肥皂泡中间位置停止——因为传导不良。这样半冻结的肥皂泡先会保持均衡状态，直到最后液体圆顶坍塌。

视频：半冻结泡泡的坍塌过程。来源：Farzad Ahmadi 和Christian Kingett（请到微信观看视频）

作者认为这项发现有助于人们更好地理解热传递现象。

摘要：Droplets or puddles tend to freeze from the propagation of a single freeze front. In contrast, videographers have shown that as soap bubbles freeze, a plethora of growing ice crystals can swirl around in a beautiful effect visually reminiscent of a snow globe. However, the underlying physics of how bubbles freeze has not been studied. Here, we characterize the physics of soap bubbles freezing on an icy substrate and reveal two distinct modes of freezing. The first mode, occurring for isothermally supercooled bubbles, generates a strong Marangoni flow that entrains ice crystals to produce the aforementioned snow globe effect. The second mode occurs when using a cold stage in a warm ambient, resulting in a bottom-up freeze front that eventually halts due to poor conduction along the bubble. Blending experiments, scaling analysis, and numerical methods, the dynamics of the freeze fronts and Marangoni flows are characterized.

阅读论文全文请访问：http://t.cn/AipA1OnK

期刊介绍：Nature Communications (https://www.nature.com/ncomms/) is an open access journal that publishes high-quality research from all areas of the natural sciences. Papers published by the journal represent important advances of significance to specialists within each field.

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（来源：科学网）