Rice University
Rice Magazine| The Magazine of Rice University | No. 1 | 2008

Paper, Plastic or Nano?

By Jade Boyd

What do you do when you have a mess? You bag it up and throw it away. But some messes — such as an oil spill — can’t be disposed of so easily. Or maybe they can.

nanobatonsMeet nanobatons: multisegmented nanowires that are made by connecting two nanomaterials with different properties. Mechanical engineering and materials scientist Pulickel Ajayan and his colleagues were working with one combination — carbon nanotubes that they fused to short segments of gold — when they noticed something peculiar.

The nanobatons spontaneously assembled by the tens of millions into spherical sacs as large as BB pellets around droplets of oil in water. Even better, the researchers found that ultraviolet light and magnetic fields could be used to flip the nanoparticles, causing the bags to instantly turn inside out and release their cargo.

In a development that could lead to new technologies for cleaning up oil spills and polluted groundwater, scientists at Rice University have shown how tiny, stick-shaped particles of metal and carbon can trap oil droplets in water by spontaneously assembling into bag-like sacs.

Ajayan says that by adding various other segments — like sections of nickel or other materials — the researchers can create truly multifunctional nanostructures. “The core of the nanotechnology revolution lies in designing inorganic nanoparticles that can self-assemble into larger structures like a ‘smart dust’ that performs different functions in the world — for example, cleaning up pollution,” Ajayan said. “Our approach brings the concept of self-assembling, functional nanomaterials one step closer to reality.”

paper nanosThe tendency of nanobatons to assemble in water-oil mixtures derives from basic chemistry. The gold end of the wire is water-loving, or hydrophilic, while the carbon end is water-averse, or hydrophobic. Ajayan, graduate student Fung Suong Ou and postdoctoral researcher Shaijumon Manikoth demonstrated that oil droplets suspended in water became encapsulated because of the structures’ tendency to align their carbon ends facing the oil. By reversing the conditions — suspending water droplets in oil — the team was able to coax the gold ends to face inward and encase the water.

“For oil droplets suspended in water, the spheres give off a light yellow color because of the exposed gold ends,” Ou said. “With water droplets, we observe a dark sphere due to the protruding black nanotubes.”

The team is preparing to test whether chemical modifications to the nanobatons could result in spheres that can not only capture but also break down oily chemicals. Another option would be to attach drugs whose release can be controlled with an external stimulus.

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The research, which was supported by Rice University, Applied Materials Inc. and the New York State Foundation for Science, Technology and Innovation, was published online in the American Chemical Society’s journal Nano Letters.