"Researchers have long been interested in making composites of nanotubes and polymers, but it can be difficult to engineer the interfaces between the two materials," said Pulickel Ajayan of Rensselaer. "We have found a way to get arrays of nanotubes into a soft polymer matrix without disturbing the shape, size or alignment of the nanotubes."

To make the arrays, Ajayan and colleagues laid down "spots" of vertically-aligned multiwalled carbon nanotubes on prepatterned SiO2/Si substrates by thermal chemical vapour deposition of ferrocene and xylene. Then they added a poly(dimethylsiloxane) (PDMS) prepolymer solution, which they proceeded to cure at 100° C for one hour. Peeling away the material from the substrate resulted in a freestanding film consisting of aligned carbon nanotubes in a transparent polymer matrix.

The structures conducted electricity well, even under large, tensile and compressive strains. "The general concept could have many applications, all the way from adhesive structures and Velcro-like materials to nanotube interconnects for electronics," said Swastik Kar of Rensselaer.

The films also exhibited excellent field emission properties, with the presence of the polymer appearing to reduce the effects of mutual screening that can occur in nanotube arrays.

"Nanotubes are very good field emitters because they have a low threshold for emission and they produce high currents," said Kar. "But when you lay nanotubes very close to each other, each tube tends to shield its neighbour from the electric field."

The researchers reported their work in Nano Letters.