Layers of ceramic cloth with interlocking nanotubes in between, is the new sandwich composite material created with significantly improved properties compared to traditional materials. The "nanotube sandwiches," which are described in the May 7 online edition of the journal Nature Materials, could find use in a wide array of structural applications. To make the new materials, the researchers deposit a forest of carbon nanotubes across the surface of a cloth woven from fibers of silicon carbide -- a ceramic compound made from silicon and carbon. The fabric layers are infiltrated with a high-temperature epoxy matrix, and then several layers of cloth are stacked on top of each other to form a three-dimensional composite "sandwich," with interlocking nanotubes acting to fasten the layers together. "This is a very nice example of how to use nanotubes to solve major existing problems, rather than going all-out to make composites based on nanotubes alone, which has proven to be a very challenging task," Ajayan says. The team has successfully made cloths up to roughly five inches by two inches, and the process is easily scalable to make larger materials, they say.

The researchers ran several experiments to test the new material's properties, and they found that theinterlocking nanotubes provided remarkable improvements in strength and toughness under various loading conditions. The materials performed extremely well in fracture tests, and they demonstrated a five-fold increase in damping -- or the ability to dissipate energy -- over the original ceramic composites without nanotubes included. This suggests that the new composites could be used in many applications where mechanical properties are important, from automobile engines to golf club shafts.

Tests also showed that both the thermal and electrical conductivity of the new composites were significantly improved, which means that they could potentially be employed as sensors to monitor crack propagation in various structures, the researchers note.

The University of Hawaii at Manoa team included Vinod Veedu, a graduate student at the Hawaii Nanotechnology Laboratory; Anyuan Cao, assistant professor of mechanical engineering; and Kougen Ma, associate director of the Intelligent and Composite Materials Laboratory. Several other Rensselaer researchers also participated in the project: Caterina Soldano, a doctoral student in physics, applied physics, and astronomy; Xuesong Li, a doctoral student in materials science and engineering; and Swastik Kar, a postdoctoral researcher in materials science and engineering.

Ajayan received funding for the project from the Focus Center-New York, which is part of the Interconnect Focus Center; and Rensselaer's National Science Foundation-funded Nanoscale Science and Engineering Center for the Directed Assembly of Nanostructures.