Washington, May 30 : Rice University researchers have found that tiny, stick-shaped particles of metal and carbon have the ability to trap oil droplets in water.
The discovery attains significance as it may help develop new technologies to clean up oil spills and polluted groundwater.
During a study, the researchers observed the tiny particles as they trapped oil droplets in water by spontaneously assembling into bag-like sacs.
The researchers said that the particles were found to assemble spontaneously by the tens of millions into spherical sacs as large as BB pellets around droplets of oil in water.
They also noticed 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.
This observation is also interesting, for it may eventually be helpful in delivering drugs.
"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. Our approach brings the concept of self-assembling, functional nanomaterials one step closer to reality," said lead research Pulickel Ajayan, Rice's Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science.
For making the multisegmented nanowires, akin to "nanoscale batons", the researcher connected two nanomaterials with different properties, much like an eraser is attached to the end of a wooden pencil.
They started with carbon nanotubes, and added short segments of gold on the top of it.
Ajayan said that the gold end of the wire was hydrophilic (water-loving), while the carbon end was hydrophobic (water-averse).
Pointing out that water-tight sacs that surround all living cells are formed by interlocking arrangements of hydrophilic and hydrophobic chemicals, the researcher said that the sac-like structures created in the study were very similar.
Ajayan said that oil droplets suspended in water became encapsulated because of the structures' tendency to align their carbon ends facing the oil.
When the researcher reversed the condition, suspending water droplets in oil, they were 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. With water droplets, we observe a dark sphere due to the protruding black nanotubes," said graduate student Fung Suong Ou, a member of the research team.
The researchers now have plans to study whether chemical modifications to the "nanobatons" may result in spheres that can both capture and break down oily chemicals.
They are hoping to attach catalysts to the water-hating ends of the nanowires that will cause compounds like trichloroethene (TCE) to break into non-toxic constituents.
The research team also has the option of attaching drugs whose release can be controlled with an external stimulus.
"The idea is to go beyond just capturing the compound and initiate a process that will make it less toxic. We want to build upon the method of self assembly and start adding functionality so these particles can carry out tasks in the real world," Ajayan said.
The research has been published online in the online edition of the journal Nano Letters.