A multiscale study of high performance double-walled nanotube-polymer fibers.

The superior mechanical behavior of carbon nanotubes (CNT) and their electrical and thermal functionalities has motivated researchers to exploit them as building blocks to develop advanced materials. Here, we demonstrate high performance double-walled nanotube (DWNT)-polymer composite yarns formed by twisting and stretching of ribbons of randomly oriented bundles of DWNTs thinly coated with polymeric organic compounds. A multiscale in situ scanning electron microscopy experimental approach was implemented to investigate the mechanical performance of yarns and isolated DWNT bundles with and without polymer coatings. DWNT-polymer yarns exhibited significant ductility of ∼20%, with energy-to-failure of as high as ∼100 J g(-1), superior to previously reported CNT-based yarns. The enhanced ductility is not at the expense of strength, as yarns exhibited strength as high as ∼1.4 GPa. In addition, the significance of twisting on the densification of yarns and corresponding enhancement in the lateral interactions between bundles is identified. Experiments at nanometer and macroscopic length scales on DWNT-polymer yarns and bundles further enabled quantification of energy dissipation/storage mechanisms in the yarns during axial deformations. We demonstrate that while isolated DWNT bundles are capable of storing/dissipating up to ∼500 J g(-1) at failure, unoptimal load transfer between individual bundles prevents the stress build up in the yarns required for considerable energy storage at the bundle level. By contrast, through polymer lateral interactions, a much better performance is obtained with the majority of energy dissipated at failure being contributed by the interactions between the polymer coating and the DWNTs as compared to the direct van der Waals interactions between bundles.