Carbon nanotube yarn and 3-D braid composites. Part II: Dynamic mechanical analysis

Macroscopic textile preforms were produced with a multi-level hierarchical carbon nanotube (CNT) structure: nanotubes, bundles, spun single yarns, plied yarns and 3-D braids. In tensile tests, reported in Part I, composites produced from the 3-D braids exhibited unusual mechanical behavior effects. The proposed physical hypotheses explained those effects by molecular level interactions and molecular hindrance of the epoxy chains with individual carbon nanotubes occupying about 40% of the composite volume. Dynamic mechanical analysis was used in this Part II to study the molecular transitions of neat epoxy resin samples and their corresponding CNT yarn composite samples with varying matrix properties. Dramatic effects on the intensity and temperature at which α-transitions occured, were recorded, as well as a marked effect on the smaller segmental motions, or β-transitions. These changes in the matrix assist in explaining the mechanical test data presented in Part I and the proposed physical explanation of those data.