Boston University Scientists Uncover the Secret to Movement in Super-cooled Water

in News Releases, Science & Technology
July 12th, 2000

Contact: Joan Schwartz, | joans@bu.edu

(Boston, Mass.) — H. Eugene Stanley and colleagues at the Center for Polymer Studies at Boston University and at the Universitá di Roma La Sapienza have created a computer model that is useful in understanding how molecules move through super-cooled water. Papers in the current issue of the journal Nature and in May 15th issue of Physical Review Letters describe the results of their work, which was supported, in part, by the National Science Foundation.

Understanding the mechanisms of super-cooled water, that is between the temperatures of 0º and –38º C, is key to understanding the processes that allow life to continue in sub-zero conditions. These conditions exist, for example, in the cells of plants that continue to metabolize through the winter, albeit at a slower pace — like a hibernating bear.

The “energy landscape,” an abstract construction representing potential energy as a set of rugged mountains. Diffusion occurs as a random selection of a particular path through the mountain passes.

Essential to this metabolism is the fact that water can exist in a viscous state, not just as the liquid we are familiar with, nor frozen (which would block all metabolism), but in the super-cooled state that scientists describe as glassy. Understanding just how these molecules of super-cooled water move, carrying nutrients to the cells of the plants in this low energy environment, has baffled scientists for some time.

“What we found,” Emilia La Nave, principal author on one of the papers, “is that how molecules diffuse through super-cooled liquid depends upon the way energy is distributed throughout the liquid – its ‘energy landscape’.”

“A useful analog,” she continues, “is a drunken mountaineer amidst a large and confusing mountain range trying to find his way home. Even though drunk, the mountaineer will be sensible enough to find the mountain passes and stumble through them rather than climb over each peak! The key to understanding the path of the mountaineer lies in the topology of the landscape he traverses – he picks the path of least resistance.”

Similarly, by analyzing the “energy landscape” of super-cooled water it is possible to make predictions about how molecules will diffuse through the liquid. This give us a better understanding about how life survives at temperatures below zero.

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