Nanolayers of water

What happens when you compress water in a nano-sized space? According to Georgia Tech physicists, water starts to behave like a solid. "The confined water film behaves like a solid in the vertical direction by forming layers parallel to the confining surface, while maintaining it's liquidity in the horizontal direction where it can flow out," said one of the researchers. "Water is a wonderful lubricant, but it flows too easily for many applications. At the one nanometer scale, water is a viscous fluid and could be a much better lubricant," added another one.

What happens when you compress water in a nano-sized space? According to Georgia Tech physicists, water starts to behave like a solid. "The confined water film behaves like a solid in the vertical direction by forming layers parallel to the confining surface, while maintaining it's liquidity in the horizontal direction where it can flow out," said one of the researchers. "Water is a wonderful lubricant, but it flows too easily for many applications. At the one nanometer scale, water is a viscous fluid and could be a much better lubricant," added another one.

Water layers at the nanoscaleThis research work has been led by Elisa Riedo, assistant professor in Georgia Tech's School of Physics, who heads the picoForce Laboratory, and Uzi Landman, director of the Center for Computational Materials Science. On the left is an illustration showing that "water behaves differently when its compressed in nano-sized channel. In these small spaces water behaves much like a solid, exhibiting high viscosity and organizing itself into layers." (Credit: Georgia Tech)

Here is how the experiments were conducted. When "Riedo and her team directly measured the force of pure water in a nanometer-sized channel, they found evidence suggesting that water was organized into layers. Riedo conducted these measurements by recording the force placed on a silicon tip of an atomic force microscope as it compressed water. The water was confined in a nanoscale thin film on top of a solid surface. As the tip compresses the water even more, the repulsive force oscillates, indicating that the water molecules are forming layers. As the tip continues to increase its pressure on a layer, the layer collapses and the water flows out horizontally."

The researchers also obtained surprising results when they measured the viscosity of water in this environment -- at least when "water was placed on top of hydrophilic surfaces that allow water to wet the solid surface, such as glass."

Riedo's team was measuring the vertical force exerted on the tip by the confined water film, they also measured the film viscosity by measuring the lateral force. They found that when water was placed on a hydrophilic surface, the viscosity began to increase dramatically as the thickness of the confined film reached the 1.5 nanometer range. As they continued to compress the water and measure the lateral forces, the viscosity increased by a factor of 1,000 to 10,000.

This research work has been published by Physical Review B under the name "Structured and viscous water in subnanometer gaps" (Volume 75, Number 11, Article 115415, March 2007). Here is a link to the abstract.

Finally, how these new water properties will be used for? Besides lubricants, they might be important for biological and pharmaceutical research.

Sources: Georgia Institute of Technology, April 25, 2007; and various websites

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