Weird world of water gets a little weirder“Thermal Conductivity Minimum: A New Water Anomaly”Journal of Physical Chemistry B

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 ACS’Journal of Physical Chemistry B.

Pradeep Kumar and H. Eugene Stanley 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 degrees below zero Fahrenheit, 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.

University of Arkansas Researchers Identify Transformation in Low-Temperature Water'L iquid- l iquid ' phase transi t ion occurs at 87 degrees below zero

Wednesday, July 10, 2013

Feng Wang, University of Arkansas

Researchers at the University of Arkansas have identified that water, when chilled to a very low temperature, transforms into a new form of liquid.

Through a simulation performed in “supercooled” water, a research team led by chemist Feng “Seymour” Wang, confirmed a “liquid-liquid” phase transition at 207 Kelvins, or 87 degrees below zero on the Fahrenheit scale.

The properties of supercooled water are important for understanding basic processes during cryoprotection, which is the preservation of tissue or cells by liquid nitrogen so they can be thawed without damage, said Wang, an associate professor in the department of chemistry and biochemistry in the J. William Fulbright College of Arts and Sciences.

“On a microsecond time scale, the water did not actually form ice but it transformed into a new form of liquid,” Wang said. “The study provides strong supporting evidence of the liquid-liquid phase transition and predicted a temperature of minimum density if water can be cooled well below its normal freezing temperature. Our study shows water will expand at a very low temperature even without forming ice.” 

The findings were published online July 8 in the journal Proceedings of the National Academy of Sciences . Wang wrote the article, “Liquid–liquid transition in supercooled water suggested by microsecond simulations.” Research associates Yaping Li and Jicun Li assisted with the study.The liquid–liquid phase transition in supercooled water has been used to explain many anomalous behaviors of water. Direct experimental verification of such a phase transition had not been accomplished, and theoretical studies from different simulations contradicted each other, Wang said.

The University of Arkansas research team investigated the liquid–liquid phase transition using a simulation model called Water potential from Adaptive Force Matching for Ice and Liquid (WAIL).

While normal water is a high-density liquid, the low-density liquid emerged at lower temperatures, according to the simulation.

The research was supported by a National Science Foundation Faculty Early Career Development Award and by a startup grant from the U of A. The University of Arkansas High Performance Computing Center provided the main computational resource for the study.