The Taoist poet Lao Tse famously wrote that water exemplifies the highest good, benefiting all and flowing easily without effort. While this makes for a lovely metaphor, there's more to H20 than is dreamt of in Lao Tse's philosophies.
Researchers at Georgia Institute of Technology have found that, at the molecular level, water exhibits viscous, even solid-like properties.
When molecules of water are forced to move through a small gap between two solid surfaces, the substance's viscosity increases by a factor of 1,000 to 10,000, approaching that of molasses.
"In this small space between surfaces, the water, which is usually very fluid, organizes itself into a new state in which well-defined layers of molecules form," said Uzi Landmann, director of the Center for Computational Materials Science at Georgia Tech, in a phone interview with Live Science.
Layering refers to a structural phenomenon in which molecules form strata between which there is very little molecular exchange. Water molecules can move about fluidly within a single layer, but not between layers. This vertical structure resembles that found in solid substances.
Landmann directed the team of physicists that simulated the experiment and predicted the layering effect. Georgia Tech experimental physicist Elisa Riedo led the team that performed the actual experiments. Together they found that the simulation predictions matched the experimental results.
The experiment observed the properties visualized in the simulation by measuring the force required to push the solid walls together. Riedo found that the force oscillates predictably, becoming largest at the point when a layer of particles is squeezed out.
Riedo and Landmann's results stand at odds with long-held beliefs about water.
"The literature almost uniformly said that water doesn't layer," said Landmann. "Without direct evidence it was inferred that water would behave differently from those liquids that do."
Previously, experiments had not measured the force directly but rather had deduced it from other properties, since techniques at the time did not allow scientists to probe the one nanometer region required to observe the effect.
The layering phenomenon has been known for about 25 years. Hexadecanes (molecule chains of 16 carbon atoms) exhibit layering properties. These are featured in many common liquids, but not in water.
Applications for the findings can be found in fields ranging from pharmaceuticals to nanotechnology. The newfound viscosity of water suggests a cheap method for lubricating very narrow regions. Water was long thought too fluid to be useful for this purpose.
But it is not merely a matter of application, insists Landmann. "The question of the nature of materials on the small scale is itself fascinating."
On that point even Lao Tse agrees: "Magnify the small, increase the few."