HIGH THROUGHPUT MODELLING OF CHIRAL CARBON NANOTHREAD BUNDLES Pei Wang Bachelor of Electrical Engineering Submitted in fulfilment of the requirements for the degree of Master of Philosophy School of Mechanical, Medical and Process Engineering Science and Engineering Faculty Queensland University of Technology 2020 Keywords Carbon nanothread Carbon nanotube Molecular dynamics simulation High-throughput computation Torsion Energy density Mechanical deformation Enantiomer Polytwistane Nanofibre Chirality High Throughput modelling of Chiral Carbon Nanothread Bundles i Abstract Carbon fibres such as ݏ݌ଷ diamond nanowire, ݏ݌ଶ carbon nanotubes, and carbyne, have received enormous interests from both scientific and engineering communities because of their outstanding chemical and mechanical properties. Among these 1D nanostructures, carbon nanotube (CNT) fibres have superior chemical, physical and mechanical properties over traditional carbon and polymeric fibres, and they are suitable for application in various fields such as power transmission lines, artificial muscles, wearable electronics, intelligent textiles, and aerospace devices. This work aims to systematically investigate the mechanical properties of individual chiral carbon nanothreads and their bundle structures through a large-scale molecular dynamics (MD) simulation method. Adaptive intermolecular reactive empirical bond order (AIREBO) potential is utilised to represent the C-C and C-H atomic interaction in the simulation. Our results show that the torsional behaviour of chiral carbon nanothreads depends on both the loading direction and the extensional pre-strain of the structure. Further, in terms of the bundle structures of the chiral carbon nanothreads, adjusting their enantiomer configurations can change their mechanical properties, such as strain energy density, elastic limit, and torsional rigidity. It is found that the chiral carbon nanothreads have unusual torsional behaviour because of their asymmetric morphologies. Adjusting the enantiomer configuration changes the properties of the nanothread bundles. Because of its excellent mechanical properties, rich individual structures, and adjustable bundle configurations, the carbon nanothread, a novel carbon nanomaterial, shows great potential as the next generation high-performance nanofibre. ii High Throughput modelling of Chiral Carbon Nanothread Bundles Table of Contents Keywords ................................................................................................................................... i Abstract ..................................................................................................................................... ii Table of Contents ..................................................................................................................... iii List of Figures ........................................................................................................................... v List of Tables ......................................................................................................................... viii List of Abbreviations ............................................................................................................... ix Statement of Original Authorship ............................................................................................. x Acknowledgements.................................................................................................................. xi Publications ............................................................................................................................ xii Chapter 1: Introduction ............................................................................................ 1 1.1 Background and Research Problem .................................................................................... 1 1.2 Objectives ........................................................................................................................... 3 1.3 Significance, Scope, and Definitions .................................................................................. 4 1.4 Thesis Outline ..................................................................................................................... 5 Chapter 2: Literature Review ................................................................................... 7 2.1 Carbon Nanofibres .............................................................................................................. 7 2.2 Molecular Dynamics Simulation ...................................................................................... 14 2.3 High-throughput Computing for Materials Discovery ..................................................... 23 2.4 Summary and Implications ............................................................................................... 26 Chapter 3: Research Design .................................................................................... 29 3.1 Modelling and MD Simulation Method for Individual Chiral NTHs .............................. 29 3.2 Modelling and MD Simulation Method for Chiral NTHs Bundles .................................. 32 3.3 MD Simulation Implementation, Data Visualization and Analysis ................................. 36 Chapter 4: Torsional Mechanical Properties of Individual Chiral NTHs .......... 41 4.1 Loading Direction Dependency of Chiral NTHs. ............................................................. 41 4.2 Tensile Pre-strain Effects on Torsional Stability of Chiral Carbon Nanothreads ............ 46 4.3 Summary ........................................................................................................................... 51 Chapter 5: Torsional Behaviour of Chiral Nanofibre Bundles with Various Enantiomer Configurations .................................................................................... 53 5.1 Torsional behaviour of PT bundles with various enantiomer configurations................... 54 5.2 Torsional Behaviour of Stiff-chiral-3 NTH Bundles with Various Enantiomer Configurations ........................................................................................................................ 58 5.3 Torsional Behaviour of (8,3) CNT Bundles with Various Enantiomer Configurations ... 61 5.4 Summary ........................................................................................................................... 65 Chapter 6: Conclusions and Limitations ............................................................... 67 High Throughput modelling of Chiral Carbon Nanothread Bundles iii 6.1 Conclusions ....................................................................................................................... 67 6.2 Limitations and future work .............................................................................................. 6 8 Bibliography ............................................................................................................. 69 Appendices ................................................................................................................ 73 Appendix A: The enumeration program. ................................................................................ 73 Appendix B: The bond breaking detection program. .............................................................. 74 Appendix C: Gravimetric densities and twist strain rate of nanofibre bundles. ..................... 75 iv High Throughput modelling of Chiral Carbon Nanothread Bundles List of Figures Figure 1.1: Thesis Outline ..................................................................................................... 6 Figure 2.1. Dimensionality and hybridisation of extended carbon molecules, nanomaterials, and solids. ................................................................................ 7 Figure 2.2: The graphene lattice making up a section of the (ͷǡͷ) single-walled carbon nanotube with graphene lattice vectors (ߙͳǡ ߙʹ), the chiral vector ܥ݄ and chiral angle ߠ marked. ܥ݄ ൌ ͷߙͳ ൅ ͷߙʹ. Adapted from [6] . .......................................................................................................... 8 Figure 2.3: Schematic diagrams of examples: a chiral armchair (n = m), (a); a chiral zigzag (n, 0) (b), chiral (്݊݉ሻǢ (c) single-walled carbon nanotubes (SWCNTs). The chiral SWCNT can exist in two different forms, or enantiomers, equivalent to a left- or right-handed screw, as illustrated in the view on the bottom right along the chiral SWCNT axis. Adapted from [6] ..................................................................................... 9 Figure 2.4: Models of carbon nanothreads sorted into three categories: stiff chiral, achiral, or axial disorder. Each structural model is shown approximately 3 nm long, regardless of its axial repeat unit, and is labelled with its conventional name and the numerical nomenclature described by Xu et al [2]. Adapted from Reference [25]. .............................. 12 Figure 2.5: Schematic view of NTH as synthesised from experiments. A segment of NTH in insets shows the structural representation of the poly- benzene rings and the Stone-Wales transformation defect (SWD). Adapted from reference [29]. ......................................................................... 13 Figure 2.6: Typical workflow of an MD simulation. Adapted from reference [37] ............ 15 Figure 2.7: Schematic view of the typical boundary conditions employed in MD simulations.