Multiscale Mechanisms of Twisted Carbon Nanotube Yarns Probed In Situ by Soft X-Rays during Tensile Loading

Resonant soft x-ray scattering (R-SoXS) can help realize the promise of data driven research in hierarchical materials whose structure spans multiple length-scales, such as carbon nanotube (CNT) assemblies. Our prior work demonstrated the wealth of high-resolution and statistical data R-SoXS provides about chemical and structural morphologies across different length scales in CNT materials [1]. CNTs are known as the strongest 1D material due to their covalent sp2 carbon bonds, hexagonal lattice, and cylindrical shape. However, piecing together CNTs into assemblies has proven to be so far a failed strategy to achieve the same elite performance metrics as individual CNTs. This highlights a critical deficiency in understanding the effects that the processing of individual nanostructures has on the performance of their derived macroscale assemblies, thereby hindering the development of a process-structure- performance map for these materials.<br/><br/>In this work, we propose a new method to decouple the distribution orientation of nanoscale tortuosity and the macroscale twist of CNT dry-spun yarns under applied loads via in- situ R-SoXS probing at high energy (1200 eV) and low energy (280 eV), respectively. With this decoupling enabled by in-situ R-SoXS, we gain new insights on the deformation mechanisms of these yarns which have been structurally reinforced with a novel vapor-phase polymer that is subsequently self-crosslinking [2]. Further, we examine how both the distribution orientation of the nanoscale tortuosity of CNT bundles and the macroscale twist of the yarns evolve as a function of applied load for different processing conditions, including yarns with plasma-enhanced surface reactivity prior to the polymer reinforcement. Better understanding of the multiscale structural behavior of CNT yarns as a function of processing will allow advances for the manufacture at large scale of products based on ultra-strong, flexible, conductive fibers for aerospace, defense, communications, wearables, and biomedical industries.<br/><br/>1. Meshot, E. R., Zwissler, D. W., Bui, N., Kuykendall, T. R., Wang, C., Hexemer, A., Wu, K. J. J., & Fornasiero, F. (2017). Quantifying the hierarchical order in self-aligned carbon nanotubes from atomic to micrometer scale. ACS nano, 11(6), 5405-5416.<br/>2. Lepro, X., Aracne-Ruddle, C., Malone, D., Hamza, H., Schaible, E., Buchsbaum, S. F., Calonico-Soto, A., Bigelow, J., Meshot, E., Baxamusa, S., & Stadermann, M. (2022). Liquid-free covalent reinforcement of carbon nanotube dry-spun yarns and free-standing sheets. Carbon, 187, 415-424.<br/><br/>Prepared by LLNL under Contract DE-AC52-07NA27344 and LDRD 20-ERD-023.