Table of Contents
2. Yarn production from carbon nanotube forests
3. Carbon nanotube fibers spun directly from furnace
4. Solution-spun carbon nanotube fibers
5. Interphase structures and properties of carbon nanotube-reinforced polymer nanocomposite fibers
6. Post-spinning treatments to carbon nanotube fibers
7. Carbon nanotube yarn structures and properties
8. Mechanics modeling of carbon nanotube yarns
9. Sensors based on CNT yarns
10. CNT yarn-based supercapacitors
11. Carbon nanotube yarn-based actuators
Organization of the book
The science and manufacturing technology around CNT fibers and yarns are still evolving. This book is aimed at providing a snapshot of these developments to people in academia and research of CNT materials, as well as product designers and processing engineers interested in the science and technology for the production, further processing, and applications of emerging high-performance textile materials.
Part 1 of the book deals with the production of CNT yarns and fibers, including “pure” CNT fibers and CNT-reinforced nanocomposite fibers. Chapter 2 discusses the probably most widely known two-step manufacturing method of CNT yarn. The first step is growing nanotubes, typically multi-walled carbon nanotubes (MWNTs) on a substrate, known variously as vertically aligned CNT arrays or CNT forests. In the second step, the CNTs in the forest are drawn out in the form of a continuous web, which is simultaneously densified into a yarn by twist insertion, liquid densification, mechanical rubbing, or other methods.
CNT fibers can also be manufactured from gaseous feedstock directly in one step, a process bearing similarities to the production of silk fibers by spiders and silkworms, and to the reaction spinning of synthetic fibers. This process is often referred to as the “direct spinning” method because a fiber is pulled out from the high-temperature furnace directly, or referred to as the floating catalyst method in contrast with the deposition of catalyst on a substrate in the two-step method discussed in Chapter 2.
The production of CNT fibers continuously from the furnace provides an effective method for production scaling up. The direct spinning method will be reviewed in Chapter 3, including the synthesis of the nanotubes, assembly of a continuous CNT network, and formation of a final fiber.
Chapter 4 provides an overview of the wet spinning of neat or nearly neat CNT fibers from bulk-grown CNTs. Premade CNTs are dissolved into a solvent (usually a strong acid) or in a suspension with the aid of surfactant, which is then formed into a fiber using wet-spinning methods that are similar to the high-throughput extrusion of textile fibers from polymers. Because the synthesis of the CNTs is separated from the formation of fibers, the wet-spinning method provides the opportunity to optimize both processes independently.
Instead of dissolving in a solvent, bulk-produced CNTs, usually a small percentage, can be dispersed in a polymer and then extruded using traditional textile fiber spinning methods. This approach is discussed in Chapter 5. Because of their superior properties and one-dimensional (1D) cylindrical geometry, CNTs are ideal fillers for reinforcing polymeric fibers. The reinforcement effect is beyond the rules-of-mixture effect because of the development of an interphase between the CNTs and the polymer. In this chapter, the structure development and property enhancement of such interphase are discussed in detail.
Many treatments have been proposed to improve the mechanical, electrical, and thermal properties of neat and composite CNT fibers, including further densification treatments based on twist insertion, lateral compression, rubbing, liquid evaporation, purification, cross-linking treatments by irradiation and polymer infiltration, and combinations of two or more of these treatments. Chapter 6 reviews the principles and procedures of these post-spinning treatments and their effects on CNT fiber properties.
Despite tremendous progresses in the last two decades, the properties of the CNT fibers and yarns produced around the world are far behind that of their constituent nanotubes. The challenge has been to organize CNTs into yarns with the best possible properties. Part 2 discusses the structures, properties, and methodology for improving the structure and properties of CNT fibers and yarns based on experiments and computational mechanics. Unlike conventional textile yarns, the strength of final CNT fibers and yarns can be rarely related back to the strength of their constituent nanotubes, mainly due to the complex nature of direct testing of individual nanotubes. Geometry of CNT yarn structure, such as nanotube alignment and packing density, is mainly investigated by adjusting the conditions of yarn manufacture and post-spinning treatments. Chapter 7 discusses the structures of CNT fibers and yarns manufactured by different methods and how their structures affect the mechanical, electrical, and thermal properties of the final fibers and yarns.
Chapter 8 reviews mechanics models of CNT yarns. General analytic models only predict qualitatively the stress distribution inside the yarn and the trends of twist-dependent yarn performances, like in conventional textile yarn mechanics. Inter-tube sliding determines the precise mechanics of a dry CNT bundle in the yarn, which can be simulated using molecular dynamics. To deal with the large number of nanotubes in a yarn, coarse-grained molecular dynamics is employed to study the microstructural evolution of the CNT structure. Multi-scale modeling is becoming an increasingly important tool to deal with the hierarchical structure of CNT yarns.
CNTs have superior mechanical, electrical, and thermal properties but their nanoscale dimensions restrict their applications. CNT yarns, being microscopic and continuous assemblies of CNTs, offer high potential for the development of applications. These multifunctional properties distinguish CNT yarns from textile fibers and metal wires, opening up the possibility of manufacturing a wide range of smart textile constructions. Part 3 reviews some of these applications, including sensing, energy storage, and artificial muscles.
CNT yarns are piezo-resistive, which can be utilized for strain measurement, material damage detection, torque measurement and motion monitoring, as well as temperature measurement and detection of various chemicals. Chapter 9 presents the operating principles of CNT yarn sensors and experimental results.
Flexible threadlike supercapacitors with high flexibility, tiny volume, and good specific performance have attracted extensive attention recently due to their potential in wearable electronics and smart textiles. CNT yarns have the advantages of high surface area, low mass density, outstanding chemical stability, and excellent electrical conductivity and thus are excellent electrode materials for threadlike supercapacitors. Chapter 10 discusses recent progresses in charge storage mechanisms, active materials, electrolytes, designs of threadlike architecture, and selfcharging supercapacitors.
CNT yarns are also promising candidates for flexible actuators, also known as artificial muscles. Chapter 11 presents a brief review on the types of CNT yarn-based actuators developed in recent years and their energy conversion mechanisms, performance metrics, and potential applications.
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