By Simon Belt
Quantum mechanics and supercomputing are allowing scientists to reveal new insights into the peculiar properties of water and how it contributes to life on Earth as we know it.
Employing a lively trio of debate, demonstrations and video to an audience of nearly 200 people, Professor Jim Matthew and Dr Mathew Probert from the University of York explained how the highly unusual temperature-dependent density of water prevents lakes and ponds from freezing from the bottom up, enabling aquatic life to survive during winter.
The reduction in density of water when it freezes explains why glass containers containing water crack when placed in a freezer.
“The use of Quantum Mechanics and supercomputers has allowed us to show that a combination of both nuclear and electronic structures of atoms has provided us with these insights,” said Dr Probert.
This conclusion has been further bolstered by evidence from experiments with “heavy water”, a form of water that has near identical chemical properties, but freezes at 11 degrees Celcius.
“Even at extremely low temperatures, atoms and molecules are never completely still and can effectively ‘tunnel’ through the walls of vessels containing them,” Dr Probert added. Such phenomena are now routinely investigated using Quantum Mechanics.
Using some clever visuals of the 3D structure of water and ice, the researchers showed how the random structure of water becomes highly ordered into cages when ice forms. This is due to weak interactions called hydrogen-bonds.
“As the temperature of water changes very slightly between four and zero degrees, the cage structure can either retain or reject further water molecules,” said Dr Probert. “This influences the density and therefore the properties of water and ice further.”
When asked why icebergs don’t taste of salt despite many being made of seawater, Dr Probert explained: “As seawater freezes, the sodium and chloride ions are expelled from the ice cage, as the water molecules prefer to bond to each other rather than to the ions”.
Greater knowledge of this latter type of process will help us to understand climate change processes on Earth, he said.