Water droplets landing on a cold surface fragment into one of two different patterns as they freeze, depending on the temperature of the surface.
Elisabeth Ghabache and her colleagues at the University of Pierre and Marie Curie in Paris used a high-speed camera to monitor the behaviour of pancake-shaped water droplets that froze on a cold steel surface after being dropped from a height of 36 centimetres. They observed no crack formation when the surface was at −20 °C (pictured left). At −30 °C and −40 °C, cracks spread from a central point towards the 'pancake' edge (centre). At −50 °C and −60 °C, the cracking occurred in a step-by-step manner, with the initial cracks splitting into newer ones at roughly 90-degree angles (right). The team used fracture modelling to determine the transition temperatures between the different fragmentation regimes.
Fragmentation occurs in many physical processes, such as bubble bursting and glass breaking. This model system could help researchers to learn more about various fracture mechanisms, the authors say.
Phys. Rev. Lett. http://dx.doi.org/10.1103/physrevlett.117.074501 (2016)
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Crack patterns in freezing water. Nature 536, 129 (2016). https://doi.org/10.1038/536129c