Press release: Fluctuating between solid and liquid
No. 232 - 07.11.2019
Göttingen chemists identify the smallest possible ice crystals
Depending on the temperature, water freezes to ice and ice melts back to water. This process, known in science as “phase transition”, is well known in everyday life. However, in order to achieve a stable lattice for ice crystals to form, a minimum number of molecules is required, otherwise the structure is unstable. Up until now, this value could only be roughly estimated. A German-American research team led by the chemist Professor Thomas Zeuch from the Institute of Physical Chemistry at the University of Göttingen has now succeeded in precisely determining the size of the smallest possible ice crystals. The research results were published in the journal Proceedings of the National Academy of Science.
Nearly 100 water molecules are needed to form an ice crystal in its smallest possible form. The scientists were also able to prove that at this scale, mixtures of amorphous liquid and well-defined crystalline clusters generally form. Using simulations, the scientists were able to calculate that the clusters each oscillate back and forth between the two states - fluctuating between solid and liquid. "The coexistence of the different states - liquid and solid – due to the oscillations of individual particles is a phenomenon of the nanoworld theoretically predicted since the1980s. But it is very difficult to prove experimentally," explains Zeuch. "And of course it contradicts our everyday experience where we can see an ice cube floating and then melting in a glass of whisky."
This new study suggests that such oscillations of tiny water crystals can occur even in cavities in proteins. This in turn is relevant for biological processes. For example, the nanocrystals could act as valves in proteins, which open (liquid state) and close (crystalline state) in response to small changes in the chemical environment. Such molecular state changes in the size range of a few nanometers are currently still very difficult to detect experimentally in cells. Zeuch and his team have investigated crystals isolated in a molecular beam for the current study. The new results were only made possible by the preliminary work of the research group of co-author Professor Udo Buck at the Max Planck Institute for Dynamics and Self-Organization. This enabled the water droplets to be prepared in the experiment at the exact temperature and size range in which they begin to form crystal structures.
Original publication: Daniel R. Mobert et al. The end of ice I. Proceedings of the National Academy of Sciences (2019). Doi: https://doi.org/10.1073/pnas.1914254116
Professor Thomas Zeuch
University of Göttingen
Institute for Physical Chemistry
Tammannstraße 6, 37077 Göttingen, Germany
Tel: +49 (0)551 39 33201