Carbon nanotubes influence materials performance. (General Developments).

Researchers from NIST, Purdue University, the University of Cincinnati, and the U.S. Air Force measured the arrangement of carbon nanotubes in suspensions in an effort to better understand their effect on the physical properties of the composite materials. Currently, the elastic modulus is improved by 100 % for nanotube-reinforced materials with 5 % reinforcement loading. At this level of loading, however, increases of the order of 1000 % can be expected. Although it is well known that the morphology of reinforcing agents has a direct influence on the performance of composites, the morphology of nanotubes in liquid suspensions or in polymer matrices is not known. This lack of understanding is at least partly responsible for the failure to realize the potential performance of nanotube-reinforced materials.

To address this need, small-angle x-ray scattering measurements on the NIST-responsible instrument at the Advanced Photon Source were used to interrogate the morphology of single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) in suspension. For MWNTs, the scattering was consistent with a rod-like morphology in which individual nanotubes were aligned in bunches with an overall diameter of approximately 500 nm. For SWNTs, a rod-like scattering profile was not observed on any length scale from 1 nm to 50 mm. Rather, disordered objects were found that were identified as a network of carbon "ropes". This arrangement of SWNTs apparently reduces the ability of the nanotubes to improve the mechanical properties of composite materials and is suspected to be the reason for the large difference between theoretical predictions and the measured properties.

CONTACT: David Black, [phone]; david. [e-mail] or Jan Ilavsky; [phone].