碳纳米管纤维的连续制备及高性能化

碳纳米管纤维是一种碳纳米管的宏观聚集体，是由碳纳米管及管束组装而成的连续纱线，具有高强、高韧、高导电等特性，在结构功能一体化复合材料、纤维状能源器件、人工肌肉以及轻质导电线缆等领域具有非常广泛的应用前景。经过近二十年的发展，碳纳米管纤维材料在连续制备技术、高性能化以及应用探索等方面相继取得了突破性的研究进展。本文总结了碳纳米管纤维材料的发展历程，对比介绍了碳纳米管纤维的不同连续制备与组装技术，重点讨论了碳纳米管纤维结构与性能之间的关联规律，并对目前碳纳米管纤维的高性能化方法进行了综述。在此基础上，对碳纳米管纤维材料的发展思路以及未来的应用方向进行了展望。

Continuous Preparation and Performance Enhancement Techniques of Carbon Nanotube Fibers

Carbon nanotube fiber (CNTF) comprises continuous yarn-like macro aggregates with a large amount of carbon nanotubes and bundles thereof. CNTFs have excellent properties, such as high strength, toughness, and conductivity, because of which, they have broad prospects in several fields, such as structure-function integrated composite materials, fibrous energy devices, artificial muscle, and lightweight conductive wire. After two decades of development, breakthroughs have been made in continuous preparation technology, performance enhancement, and application exploration of CNTF materials. In this review, the development history of CNTF materials is summarized, and various continuous preparation technologies of CNTFs, including wet spinning, array spinning, and floating catalyst chemical vapor deposition (FCCVD) direct spinning, are described and compared. The wet spinning technology for fabricating CNTFs can be easily scaled due to its similarity to the conventional wet spinning technology used for fabricating high-performance fibers, while the obtained CNTFs have relatively high conductivity. The main challenges in wet spinning are the mass preparation and appropriate dispersion of high-quality carbon nanotubes (CNTs) with large aspect ratios. The array spinning technology can produce CNTFs with high purity and controllable structures, and its challenges are the relatively low preparation efficiency and high cost, because of which, it is challenging to meet the needs of large-scale applications. The FCCVD direct spinning technology can continuously produce CNTFs with relatively high strengths and at low cost, and it is easily adaptable for large-scale fabrication. The main drawbacks of CNTFs obtained from direct spinning are the relatively high impurity content and nonuniform CNT structures. Since CNTFs were first reported in 2000, one of the major challenges has been transferring the excellent properties of individual CNTs to the macroscopic assemblies of CNTs. To answer this question, the correlation between the structures and properties of CNTFs is discussed in detail, and contemporary techniques used for the enhancement of mechanical and electrical properties of CNTFs are reviewed. Based on the fiber fracture mechanism of slippage between CNTs, typical mechanical performance enhancement techniques include manipulating the CNT structures (namely wall number, diameter, aspect ratio, and collapse state), aligning the CNT along the fiber axis, enhancing the packing density and the interaction between CNTs, and combining with other reinforcing materials. The electrical performance of CNTFs is attributed to a 3D hopping electron transport mechanism in CNTFs. Conductivity enhancement techniques mainly include improving the assembly structure of CNTFs, using conductive materials as fillers between the CNTs, oxidative p-doping, and combining with metallic conductors. Finally, the main challenges in terms of performance enhancement and large-scale fabrication are discussed, and the development directions of CNTF materials are proposed.