Discovery sheds light on flow of water in carbon nanotubes

Wednesday, September 17, 2008 

This illustration demonstrates one form a carbon nanotube can take.
Image: Arnero.

Experiments during the past several years examining membranes formed from carbon nanotubes have demonstrated potential for a variety of applications, perhaps most notably economical filtration of water for desalination. But something that has consistently confused researchers is that the rate of flow for water passing through these special membranes is considerably higher than would be predicted by classical physics. In some experiments the flow rate was up to 10,000 times the speed expected. In addition, recent measurements by a team at Lawrence Livermore National Laboratory conducted via nuclear magnetic resonance showed that the water passing through nanotubes exhibits very different properties in comparison to bulk water.

In a press release Tuesday the News Bureau of the University of Illinois at Urbana-Champaign highlighted a recent finding that offers one possible explanation for the phenomenon. The research, published in Physical Review Letters last month (doi:10.1103/PhysRevLett.101.064502 ), used molecular modeling to analyze the predicted behavior and interactions of individual water molecules passing through a nanotube.

UIUC researchers Narayana R. Aluru, a professor of mechanical science and engineering, and doctoral student Sony Joseph found that the chemical polarity of H₂O and what they describe as "confinement effects" within the bounds of smaller nanotubes cause the molecular movements to couple. Due to the water molecules interacting and orienting themselves in response to one another they flow in a more orderly helical or corkscrew pattern through the nanotube. This flow pattern may explain some of the experimental results obtained by other scientists.

Hopefully this discovery is another step towards an affordable technology to produce plentiful potable water for drinking, irrigation of crops, and other purposes, a vital resource that is in short supply in many parts of the world.

Sources

• Press Release: James E. Kloeppel. "Simulations help explain fast water transport in nanotubes" — University of Illinois at Urbana-Champaign, September 16, 2008
• "Nanotube membranes for energy efficient desalination" — ECOS (CSIRO magazine), July 9, 2007
• Press Release: Anne M. Stark. "LLNL researchers peer into water in carbon nanotubes" — Lawrence Livermore National Laboratory, June 25, 2008
• Aditi Risbud. "Cheap Drinking Water from the Ocean" — Technology Review, June 12, 2006