We already know that water exists in three states – solid, liquid, and gaseous. But, scientists at the US Department of Energy’s Oak Ridge National Laboratory (ORNL) have discovered a bizarre and unexpected behavior of water molecule under extreme confinement that is unmatched by any of these previously known states.
As per the paper published in Physical Review Letters, the water molecule – in an incredibly small space under extreme pressure, or in other word, when confined in hexagonal ultra-small channels – 5 angstrom across – of the mineral beryl – exhibited a characteristic generally seen at the much smaller quantum level, known as tunneling.
Quantum tunneling basically means the passage of a particle, or in this case a molecule, through a seemingly impassable energy barrier. Even if the energy of a particle (or molecule) may be too low to overcome a barrier in classical physics, the particle (or molecule) can still cross the barrier and be on both side of it at at once or anywhere between (as a consequence of its quantum-mechanical wave properties).
“At low temperatures, this tunneling water exhibits quantum motion through the separating potential walls, which is forbidden in the classical world,” said the study’s lead author Alexander Kolesnikov of ORNL’s Chemical and Engineering Materials Division.
“This means that the oxygen and hydrogen atoms of the water molecule are ‘delocalized’ and therefore simultaneously present in all six symmetrically equivalent positions in the channel at the same time. It’s one of those phenomena that only occur in quantum mechanics and has no parallel in our everyday experience.”
The discovery of this fourth state of water molecule was made possible with experiments at ORNL’s Spallation Neutron Source and the Rutherford Appleton Laboratory in the United Kingdom. And, it demonstrates features of water under extreme confinement in rocks, soil and cell walls.
Researchers believe the existence of this fourth state of water, known as the tunneling, should help scientists better describe the thermodynamic properties and behavior of water in highly confined environments such as water diffusion and transport in the channels of cell membranes, in carbon nanotubes and along grain boundaries and at mineral interfaces in a host of geological environments.
“This discovery represents a new fundamental understanding of the behavior of water and the way water utilizes energy,” explains Lawrence Anovitz. “It’s also interesting to think that those water molecules in your aquamarine or emerald ring – blue and green varieties of beryl – are undergoing the same quantum tunneling we’ve seen in our experiments.”
Previous studies have observed tunneling of atomic hydrogen in other systems, researchers said that the discovery that water exhibits such tunneling behavior is unprecedented. Using the neutron scattering and computational chemistry experiments, the researchers were able to showed that, in the tunneling state, the water molecules are delocalized around a ring so the water molecule assumes an unusual double top-like shape.
“The average kinetic energy of the water protons directly obtained from the neutron experiment is a measure of their motion at almost absolute zero temperature and is about 30 percent less than it is in bulk liquid or solid water,” Kolesnikov said. “This is in complete disagreement with accepted models based on the energies of its vibrational modes.”
Researchers hope the discovery of this fourth state of water could have implications wherever water is found in incredibly tight spaces such as in cell membranes or inside carbon nanotubes.
- Sources: ORNL, Gizmag
- Reference: Quantum Tunneling of Water in Beryl: A New State of the Water Molecule