Unmatched by any known gas, liquid or solid states, unique and unexpected behavior of water molecules under extreme confinement has been revealed by neutron scattering and computational modeling.
Oak Ridge National Laboratory researchers have reported a new tunneling state of water molecules confined in hexagonal ultra-small channels, 5 angstrom across, of the mineral beryl. An angstrom is 1/10-billionth of a meter, and individual atoms are typically about 1 angstrom in diameter.
The discovery, made possible with experiments at ORNL’s Spallation Neutron Source and the Rutherford Appleton Laboratory in the United Kingdom, demonstrates features of water under ultra confinement in rocks, soil and cell walls, which scientists predict will be of interest across many disciplines.
Lead author Alexander Kolesnikov of ORNL’s Chemical and Engineering Materials Division, said:
The existence of the tunneling state of water shown in ORNL’s study 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.
New Fundamental Understanding
ORNL co-author Lawrence Anovitz noted that the discovery is apt to spark discussions among materials, biological, geological and computational scientists as they attempt to explain the mechanism behind this phenomenon and understand how it applies to their materials.
While previous studies have observed tunneling of atomic hydrogen in other systems, the ORNL discovery that water exhibits such tunneling behavior is unprecedented. The neutron scattering and computational chemistry experiments 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.
First principle simulations made by Narayani Choudhury of Lake Washington Institute of Technology and University of Washington-Bothell showed that the tunneling behavior is coupled to the vibrational dynamics of the beryl structure.
Image: by Jeff Scovil