Chinese scientists have provided experimental information on the existence and temperature-dependent size of critical ice nuclei for the first time.
Water freezing is ubiquitous, but the process of how water turns into ice at the micro level is unknown. Ice nucleation is the controlling step in water freezing and has, for nearly a century, been assumed to require the formation of a critical ice nucleus, according to the classical nucleation theory. But there has been no direct experimental evidence for the existence of such a nucleus, owing to its transient and nanoscale nature.
Researchers from the Institute of Chemistry, Chinese Academy of Sciences and the University of the Chinese Academy of Sciences creatively probed the existence of a critical ice nucleus and its size for ice formation with graphene oxide nanosheets.
In a paper published in the journal Nature, researchers used different-sized graphene oxide nanosheets to detect the critical size of the ice nucleus.
They inferred from the experimental data and theoretical calculations that the critical size of the graphene oxide reflects the size of the critical ice nucleus, which in the case of sufficiently large graphene oxides sits on their surface and gives rise to ice formation behavior consistent with classical nucleation theory.
"This experiment can be understood like this: using nanoparticles with a determined size as rulers to measure the critical ice nucleus and continuously reducing the temperature to make the ice nucleus size reach the required critical size. When the ice nucleus size is exactly the same as the size of the nanoparticles, it is easy to form a critical ice nucleus," Wang said.
The research has deepened the microscopic understanding of water freezing and has also provided important theoretical guidance for the application of artificial ice control. It will play a vital role in the fields of chemical industry, cryobiology and materials science. (Xinhua)
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