Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Water flows like molasses on the nanoscale

27.04.2007
A Georgia Tech research team has discovered that water exhibits very different properties when it is confined to channels less than two nanometers wide – behaving much like a viscous fluid with a viscosity approaching that of molasses. Determining the properties of water on the nanoscale may prove important for biological and pharmaceutical research as well as nanotechnology. The research appears in the March 15 issue of the journal Physical Review B.

In its bulk liquid form, water is a disordered medium that flows very readily. When most substances are compressed into a solid, their density increases. But water is different; when it becomes ice, it becomes less dense. For this reason, many scientists reasoned that when water is compressed (as it is in a nanometer-sized channel), it should maintain its liquid properties and shouldn't exhibit properties that are akin to a solid. Several earlier studies came to that very conclusion – that water confined in a nano-space behaves just like water does in the macro world. Consequently, a number of scientists considered the case to be closed.

But when Georgia Tech experimental physicist Elisa 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.

"Since water usually has a low viscosity, the force you would expect to feel as you compress it should be very small," said Riedo, assistant professor in Georgia Tech's School of Physics. "But when we did the experiment, we found that when the distance between the tip and the surface is about one nanometer, we feel a repulsive force by the water that is much stronger than what we would expect."

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.

"In effect, the confined water film behaves effectively like a solid in the vertical direction by forming layers parallel to the confining tip and surface, while maintaining it's liquidity in the horizontal direction where it can flow out – resembling some phases of liquid crystals," said Uzi Landman, director of the Center for Computational Materials Science, Regents' and Institute professor, and Callaway Chair of Physics at Georgia Tech.

A theoretical physicist, Landman conducted the first-ever computer simulations of these forces for tip-confined water films and found good correspondence between his team's theoretical predictions and the experiments.

So why did Riedo and Landman's results differ from their peers? According to Landman, most previous studies on confined water were limited by technology at the time and could not directly measure the behavior in the last two nanometers. Instead they had to measure other properties and infer the forces acting in films of one nanometer thickness or less.

"If you want force, it is preferable to measure it," he said. "This is the first experiment to directly measure the force and it's the first simulation done of these forces. The fact that we have direct measurements married with theoretical results is rather conclusive."

Riedo and Landman conducted their experiments in several different environments. They found that the layering effect was more pronounced when water was placed on top of hydrophilic surfaces that allow water to wet the solid surface, such as glass. When the water was confined by hydrophobic surfaces where water tends to bead up, like graphite, the effect was still present, but less pronounced.

At the same time, 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.

On hydrophobic surfaces, they did not see such an increase in viscosity. The results of the molecular dynamics simulations support these findings, showing a dramatically decreased mobility for sub-nanometer thick water films under hydrophilic confinement.

"Water is a wonderful lubricant," said Riedo, "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."

Understanding the properties of water at this scale could also be important for biological and pharmaceutical research, especially in understanding processes that depend on hydrated ionic transport through nanoscale channels and pores.

Riedo and Landman's next steps are to introduce impurities in the water to study how that affects its properties.

David Terraso | EurekAlert!
Further information:
http://www.gatech.edu

More articles from Physics and Astronomy:

nachricht Tune your radio: galaxies sing while forming stars
21.02.2017 | Max-Planck-Institut für Radioastronomie

nachricht Breakthrough with a chain of gold atoms
17.02.2017 | Universität Konstanz

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Impacts of mass coral die-off on Indian Ocean reefs revealed

21.02.2017 | Earth Sciences

Novel breast tomosynthesis technique reduces screening recall rate

21.02.2017 | Medical Engineering

Use your Voice – and Smart Homes will “LISTEN”

21.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>