Liquids cooled below their freezing point can exist in this supercooled state for a long time before an external perturbation or a rare spontaneous fluctuation initiates the transition and the liquid freezes, a process known as nucleation and growth. According to classical nucleation theory, formulated early in the last century, this process occurs through the formation of a crystalline nucleus, which will spontaneously grow to transform the whole system once it has reached a certain critical size. Using advanced computer simulations, Christoph Dellago from VICoM and his colleagues from the University of Amsterdam have now found that the nucleus size is not sufficient to predict the likely fate of a crystalline.  In their simulations, they observed that small nuclei that were thought to be destined to shrink actually grew, while large nuclei that were expected to grow further based on their size dissolved again. So there must be additional properties that govern the fate of a crystalline nucleus. But what would theses be? Analyzing the statistical properties of crystallization trajectories, Dellago and colleagues, showed that nuclei are not homogeneous objects but rather structured in layers, like an onion. The innermost core consits of particles that are already in the crystalline state. This core is surrounded by a cloud of particles that are partially ordered, but still differ from real crystals. When both the size of the core and the size of the surface cloud are taken into account, one can predict with high accuracy whether or not the transformation will occur or not. Thus, the surface cloud provides the missing parameter required for a complete understanding of the freezing of supercooled liquids.

DOI:10.1103/PhysRevLett.106.085701
PACS:64.70.pv, 81.10.Aj

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Nucleus with cloud.

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P11 Nucleation and Self-Assembly in Soft Matter Systems: From the Molecular to the Mesoscopic Scale / Christoph Dellago

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University of Vienna / Öffentlichkeitsarbeit und Veranstaltungsmanagement / Medienportal

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University of Vienna / Öffentlichkeitsarbeit und Veranstaltungsmanagement / Uni-View

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