Ice nucleation is the step that controls how water freezes. Scientists have long assumed it requires formation of a critical ice nucleus. However, no direct experimental evidence had been found to prove the existence of such a nucleus, due to its transient and nanoscale nature. 

In 2019, the situation changed as a team of researchers from the Institute of Chemistry of the Chinese Academy of Sciences and the University of the Chinese Academy of Sciences creatively used graphene oxide nanosheets to explore the critical ice nucleus and experimentally verify its existence for the first time. The scientists also explored the relationship between the size of the critical ice nucleus and the degree of supercooling of the related water droplets. 

The research has deepened the microscopic understanding of how water freezes and provides new ideas for anti-icing control, cryobiology and materials science. 

Results of the study were published online in Nature in December 2019. 

Artistic rendering of critical ice nuclei atop nanosheets 

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