Wednesday, February 14, 2007

Researchers Develop Method to Control Water Flow Through Carbon Nanotubes

Researchers at Rensselaer Polytechnic Institute have developed a new method of controlling the flow of water through carbon nanotube membranes with an unprecedented level of precision. That may not sound that interesting, but it could lead to technologies designed to transform salt water into pure drinking water almost instantly, or to immediately separate a specific strand of DNA from the biological jumble.

Nanotube membranes have fascinated researchers with their combination of high flow rates and high selectivity, allowing them to filter out very small impurities and other organic materials like DNA and proteins from materials with high water content. The problem is that nanotube arrays are hydrophobic, strongly repelling water.

The researchers found a way to use low-voltage electricity to manipulate the flow of water through nanotubes. They discovered that when the nanotube’s membrane is given a small positive potential of only 1.7 volts, and the water is given a negative potential, the nanotubes quickly switch from repelling water to pumping water through the tube. When the charge on the water is raised, the water flows through at an exponentially faster rate. When the experiment is reversed with a negatively charged nanotube, it takes much higher voltage (90 volts) to move the water through the tube.

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