Multiscale Mechanisms of Twisted Carbon Nanotube Yarns Probed <i>In Situ</i> by Soft X-rays during Tensile Loading.

Abstract

Piecing together carbon nanotubes (CNTs) into assemblies has so far failed to achieve the same elite strength performance metrics as individual CNTs, highlighting a critical deficiency in understanding the effects that the processing of individual nanostructures have on the performance of their derived macroscale assemblies, thereby hindering the development of a process-structure-performance map for these materials. In this work, we propose a method to decouple the distribution orientation of nanoscale tortuosity and the microscale twist of CNT dry-spun yarns under applied loads via <i>in situ</i> soft X-ray probing at high energy (1200 eV) and low energy (280 eV), respectively. With this decoupling enabled by <i>in situ</i> soft X-ray scattering, we acquired a deeper understanding of the deformation mechanisms of these yarns. We found that for untreated yarns, the twist angle of collective CNT bundles at the macroscale is more sensitive to applied stress than the nanoscale alignment distribution. We also found that increasing nominal twist densities of yarns as well as increased strengthening via plasma treatments and polymer infiltration act to decrease the yarns' sensitivity to realignment at the nanoscale and prevent failure by the slip mechanism.