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Strange,
stranger, strangest! To the weird nature of one of the simplest
chemical compounds—the stuff so familiar that even non-scientists know
its chemical formula—add another odd twist. Scientists are reporting
that good old H2O, when chilled below the freezing point, can shift into
a new type of liquid. The report appears in American Chemical Society’s Journal of Physical Chemistry B.
Pradeep
Kumar of Rockefeller University New York and H. Eugene Stanley of
Boston University explain that water is one weird substance, exhibiting
more than 80 unusual properties, by one count, including some that
scientists still struggle to understand. For example, water can exist in
all three states of matter (solid, liquid,gas) at the same time. And
the forces at its surface enable insects to walk on water and water to
rise up from the roots into the leaves of trees and other plants. In
another strange turn, scientists have proposed that water can go from
being one type of liquid into another in a so-called “liquid-liquid”
phase transition, but it is impossible to test this with today’s
laboratory equipment because these things happen so fast. That’s why
Kumar and Stanley used computer simulations to check it out.
They
found that when they chilled liquid water in their simulation, its
propensity to conduct heat decreases, as expected for an ordinary
liquid. But, when they lowered the temperature to about -54 F, the
liquid water started to conduct heat even better in the simulation.
Their studies suggest that below this temperature, liquid water
undergoes sharp but continuous structural changes whereas the local
structure of liquid becomes extremely ordered— very much like ice. These
structural changes in liquid water lead to increase of heat conduction
at lower temperatures. The researchers say that this surprising result
supports the idea that water has a liquid-liquid phase transition.
The authors acknowledged funding from the National Science Foundation and the National Academies Keck Futures Initiatives.
