Water is one of the most peculiar liquids, but scientists are finally beginning to understand its strange behavior.
As part of a new investigation into water's behavioral anomalies, scientists at the University of Bristol used computer models to deprogram water's unique physical attributes. The results of the study, published this week in the journal PNAS, offer scientists fresh insights into what makes water so special.
Unlike most liquids, water expands when it cools to temperatures below four degrees Celsius, causing lakes to freeze from the top instead of the bottom. Water also has unusually high surface tension and loses viscosity when compressed.
Water's many unique physical attributes aren't just peculiar, they're essential to a variety of natural processes and systems. In many ways, water's oddities make life possible.
When researchers compare water to other liquids, they often get the impression that water has been fine-tuned to behave the way it does. With the help of sophisticated computer models designed to analyze water's molecular properties, Bristol scientists worked to "un-tune" water.
Scientists used the models to transform water into a simple liquid. For example, scientists programmed water to become denser when it freezes, causing ice to sink instead of float.
"With this procedure, we have found that what makes water behave anomalously is the presence of a particular arrangement of the water's molecules, such as the tetrahedral arrangement, where a water molecule is hydrogen-bonded to four molecules located on the vertices of a tetrahedron," John Russo, a professor of mathematics at Bristol, said in a news release. "Four of such tetrahedral arrangements can organise themselves in such a way that they share a common water molecule at the centre without overlapping."
Water's combination of this well-ordered molecular arrangement with disordered arrangements gives the liquid its unusual qualities.
"We think this work provides a simple explanation of the anomalies and highlights the exceptional nature of water, which makes it so special compared with any other substance," Russo said.
