Researchers at the University of Pennsylvania have devised a new method for aligning isolated single wall carbon nanotubes and, in the process, have created a new kind of material with liquid crystal-like properties, which they call nematic nanotube gels. The gels could potentially serve as sensors in complex fluids, where changes in local chemical environment, such as acidity or solvent quality, can lead to visible changes in the gel shape. The researchers describe their findings in the current issue of Physical Review Letters.
Single wall carbon nanotubes have astounded researchers with their remarkable strength and their ability to conduct heat and electricity. For many of their potential applications, however, these nanotubes work best when they are aligned parallel to one another, without forming aggregates or bundles. In solutions with low concentrations of single wall carbon nanotubes, the nanotubes are isotropic, or not oriented in a particular direction. If the concentration of the single wall carbon nanotubes is increased sufficiently, it becomes energetically favorable for the nanotubes to align. This is the nematic phase that many researchers have sought to create and utilize.
"Unfortunately, experience has shown that single wall carbon nanotubes tend to clump together or form three-dimensional networks in water at concentrations where theories otherwise predict they will form this nematic liquid crystal phase," said Arjun Yodh, senior author and a professor in Penn Department of Physics and Astronomy. "Our gels effectively increase the concentration of isolated single wall carbon nanotubes without allowing them to bundle up or form networks."
Greg Lester | University of Pennsylvania
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