A high-resolution inelastic x-ray scattering technique was used to measure the strong bond involving a hydrogen atom sandwiched between two oxygen atoms. This hydrogen bond is a quantum-mechanical phenomenon responsible for various properties of water, including viscosity, that determine a liquid's resistance to flow or to change shape.
The technique demonstrated that it is possible to probe real-space, real-time dynamics of water and other liquids. Previous studies have provided snapshots of water's atomic structure, but little is known about how water molecules move. The hydrogen bond has a strong effect on the dynamic correlation between molecules as they move through space and time, but previously, data by optical laser spectroscopy has yielded broad or “hazy” results with unclear specificity.
For a clearer picture, an advanced x-ray technique known as inelastic x-ray scattering was used to determine molecular movement. The dynamics of oxygen-to-oxygen bonding between water molecules is surprisingly not random, but highly coordinated. When the bond between water molecules is disrupted, the strong hydrogen bonds work to maintain a stable environment over a specific period of time. The amount of time it takes for a molecule to change its “neighbor” molecule determines the water's viscosity. This new discovery would stimulate further studies on exerting control over the viscosity of other liquids.
The work is a springboard to more advanced research to further determine the origin of viscosity and other dynamic properties of liquids, and to develop new types of semiconductors and batteries.