Why does supercooling water work

In the two-dimensional analogue, a plane cannot be filled by pentagons only, whereas triangles, rectangles or hexagons can fill a plane perfectly. In this example, pentagons are an obstacle to crystallization. Until today there was no experimental proof that this five-fold coordinated structures are at the origin of supercooling. The researchers from the CEA, CNRS and ESRF studied the structure of a particular liquid, a gold-silicon alloy, in contact with a specially decorated silicon surface, where the outermost layer of the solid featured pentagonal atomic arrangements.

Their findings confirmed that a strong supercooling effect took place. The team performed the control experiment with the same liquid exposed to three-fold and four-fold coordinated surfaces, which reduced the supercooling effect dramatically. Droplet of a gold-silicon liquid alloy on a silicon surface. Pentagonal clusters formed at the interface exhibit a denser structure compared to solid gold and prevent the liquid from crystallization at temperatures as low as Kelvin below the solidification temperature.

Graphics: M. Now, however, a novel experiment has allowed researchers their first glimpse into the microscopic structure of supercooled water. But, for now, that's just a theory. But, crucially, enough liquid water remains in some of the droplets for the scientists to study. Perpendicular to the beam of water drops is an X-ray laser shooting extremely brief pulses, just 50 femtoseconds long i.

By studying the diffraction pattern that results when one of these pulses encounters a droplet of supercooled water, the scientists can probe the structural makeup of the droplets. A liquid below its freezing point will crystallize in the presence of a seed crystal or nucleus around which a crystal structure can form.

However, lacking any such nucleus, the liquid phase can be maintained all the way down to the temperature at which crystal homogeneous nucleation occurs. The homogeneous nucleation can occur above the glass transition where the system is an amorphous - that is, non-crystalline-solid. Reference Terms.

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