"Curiosity prompted us to sonicate a suspension of carbon nanotubes in room-temperature ionic liquids," researcher Takanori Fukushima told nanotechweb.org. "We found that under certain conditions the system becomes viscous, but it soon returned to the suspension. We could not reproduce this interesting phenomenon, but later found that grinding of the suspension gives a reproducible result."

The scientists ground room-temperature ionic liquids of imidazolium ions with single-walled carbon nanotubes, a process that resulted in the formation of physical gels that were highly viscous. These so-called "bucky gels" were thermally stable, but the researchers found they could remove the ionic liquid by putting the gel on adsorbent paper.

"Since bucky gels of ionic liquids are soft materials, one can readily process bucky cables, bucky films, bucky sheets, etc, and even print any patterns (bucky inks)," said Fukushima.

The team also made a bucky gel using a polymerizable ionic liquid. They polymerized the ionic liquid by applying a heat treatment, and the resulting single-walled carbon nanotube polymer composite, which contained 3.8% by weight of nanotubes, had a dynamic hardness almost 400% higher than a sheet of the polymer prepared without nanotubes. This "bucky plastic" also showed a conductivity of 0.56 S/cm at room temperature, in contrast to the polymer alone, which is generally an insulator.

The technique could find use in making electroconductive and high-strength plastics, actuators, transistors, electroconductive inks for patterning, and electrochemical devices such as capacitors, batteries and fuel cells.

"We plan a wide-ranging application of this processing method to carbon allotropes other than single-walled carbon nanotubes," added Fukushima. "We will also investigate a wide variety of electrochemical applications of bucky gels and bucky plastics. In addition, we will attempt to further enhance the mechanical properties and electroconductivities of the materials."

The researchers reported their work in Science.