Radial thermal expansion of purified multiwall carbon nanotubes measured by X-ray diffraction

The thermal expansion in the radial direction (stacking axis of graphene sheets) of multiwall carbon nanotubes (MWNTs) is measured in the temperature range from 10 to 320 K. The sample includes in excess of 85% by weight of MWNTs. The radial thermal expansion of MWNTs is found to be almost the same with the c-axis thermal expansion of graphite. This result strongly challenges the concentric structural model for MWNTs, suggesting the appropriateness of the scroll type model instead of the concentric one.