Science-- there's something for everyone

Thursday, May 6, 2010

Supercooling explained

Supercooling is the phenomenon, first discovered by Daniel Fahrenheit in 1724, whereby materials remain in their liquid state at much lower temperatures than should be expected. For example, the water droplets that make up clouds are far below freezing temperature, yet they don’t solidify. Why not?

Scientists from the Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), the Centre National de Recherche Scientifique (CNRS) and the European Synchrotron Radiation Facility (ESRF) tested the hypothesis that it is the internal structure of molecules within a liquid that allows supercooling to occur. In order for something to crystallize, or solidify, all the molecules must be packed together in a regular order. If you picture a 2D space, you can see that some shapes (triangles or squares) will easily pack together, whereas others (circles) will not.

The team used a gold-silicon alloy as the liquid in their tests. When placed on a molecularly pentagonal surface the droplets displayed a strong supercooling effect. The effect was greatly diminished when the contact surfaces were three or four-fold. This appears to confirm the theory that molecular shape affects whether or not a liquid can be supercooled.

One thing’s for sure. How ever it works, supercooling is super cool!