Review Of Carbon Nanotube Fibers Published By Suzhou Nanotechnology Institute

Carbon nanotubes (CNTs), a potential super material, are the ideal core materials for future super structure and carbon based semiconductor devices. Assembling carbon nanotubes into macromolecules (such as fibers, membranes and foams) is one of the most important ways to achieve the macroscopic application of carbon nanotubes.

Carbon nanotubes (CNTs) are one dimensional continuous assembly of carbon nanotubes. They can be used not only by themselves, but also by braiding to form two-dimensional or three-dimensional braided structures. In recent twenty years, people have been committed to developing the continuous spinning process of carbon nanotube fibers, revealing the process structure performance relationship of carbon nanotube fibers, and developing the engineering applications of carbon nanotube fibers.

A large number of studies have shown that carbon nanotube fibers have wide application prospects in structural and functional integrated composites, fiber energy devices, artificial muscles and light conductive cables. Unfortunately, from the single carbon nanotube at the nanometer scale to the carbon nanotube fiber at a macro scale, the efficiency of carbon nanotubes in the performance of force, electricity and heat is even less than 10%, which limits the engineering application of carbon nanotubes. Understanding and clarifying the process structure performance relationship of carbon nanotube fibers is the key to further enhance the performance of carbon nanotube fibers.

Since the establishment of the Li Qingwen team of the Suzhou Institute of nanotechnology and nano Bionics in the Chinese Academy of Sciences in 2007, a large number of basic research and application development have been carried out in the field of carbon nanotubes. Recently, the team was invited to write a review article (Advanced 201902028) in the Journal of advanced Materials (DOI:10.1002/adma. DOI:10.1002/adma.). We systematically reviewed the work done in the past twenty years on the basic physical properties of carbon nanotubes, and prospected the future development of carbon nanotubes.

Reviewing the development history of carbon nanotube fibers, we can find that China has carried out carbon nanotube fiber research earlier in the world. In 2000, French scientists first reported the preparation of continuous carbon fiber materials with carbon nanotubes content up to 50% by wet spinning process, and opened the prelude to the study of carbon nanotube fibers. In 2002, Professor Wu Dehai of Tsinghua University and the Rensselaer Polytechnic Institute professor P. M. Ajayan first reported the use of floating chemical vapor deposition to prepare carbon nanotube bundles with diameters of about 300 to 500 microns. The length of the carbon nanotube bundles was 20 centimeters. In the same year, Professor Fan Shoushan of the Tsinghua University first reported the method of preparing carbon nanotube fibers from carbon nanotube arrays. In 2004, Chinese scientist Li Yali, in collaboration with Professor Alan Windle, achieved the continuous preparation of carbon nanofibers by floating catalytic chemical vapor deposition. In the meantime, American scientists reported the preparation of pure carbon nanotube fibers by wet process. In 2018, Professor Wei Fei of Tsinghua University reported the centimeter scale carbon nanotube bundles with a strength of 80 GPa. After successful assembly of carbon nanotubes at the macro scale, the research of carbon nanotubes has rapidly developed. In the 20 years of development, there have been three stages of development: (1) the exploratory stage of the carbon nanotube fiber spinning method is based on the wet spinning process of solidification, the vertical spinning of carbon nanotube arrays, and the direct spinning of carbon nanotubes gel based on the growth process as the main method of preparation. (2) aiming at the rapid development of carbon nanotube fibers for continuous preparation, improvement of basic properties and the development of functional properties; (3) the development of carbon nanotube fibers has entered the critical stage of industrial application. Overall, scientists have been around 2000.

Based on different spinning methods, carbon nanotube fibers exhibit extremely rich assembly structures. Compared with its microstructure, the orientation, tightness and entanglement of carbon nanotubes in fibers, radial distribution of fibers, surface morphology and other structural properties further determine the macroscopic physical properties of fibers. More importantly, if we improve the fiber assembly structure, we can effectively control the transmission of heat, power and heat between pipes, which is the key to improve the performance of fibers and give full play to the performance of single nanotubes.

In the summary of the research progress, the author describes the force, electricity and thermal properties of carbon nanotube fibers respectively. In terms of mechanical properties, the breaking strength and elastic modulus of fibers can be significantly improved by solvent densification, mechanical densification, step drafting, introduction of polymer network structure in fibers, and induced covalent bonding between tubes. On the other hand, the fiber rich interface structure has brought about a variety of energy dissipation processes, making carbon nanotube fibers (films and composite materials) exhibit dynamic mechanical properties such as damping and creep, which are not available in traditional carbon fibers. In addition, the yarn structure and unique flexibility of fibers show unique advantages in the fields of rotary drive and biological electrodes.

Carbon nanotube fibers are excellent "guides". After conducting the electron transition channels between the tubes through doping means, the conductivity of the fibers exceeds the limits of the metal conductors in terms of specific conductivity, showing a development advantage in the direction of lightweight conductors. With the combination of metal and the thermal conductivity of carbon nanotubes, the limiting current carrying capacity of the composite conductors can be greatly improved, which is expected to replace traditional metal conductors in the future applications of ultra high current. Due to the unique assembly characteristics, the thermal radiation on the surface of the fiber is especially significant, resulting in a great difference between the apparent thermal conductivity and the actual thermal conductivity in the actual measurement, and the former diverges rapidly with the increase of the sample size. For this reason, besides optimizing the fiber structure to improve the phonon transport between tubes, the further development of the test method is also an important part of the thermal conductivity study of carbon nanotubes.

In this review, the author introduces the theoretical research on the force, electricity and thermal properties. It points out that the further improvement of fiber performance and the foundation of industrialization realization still lie in the deep understanding of the relationship between the three aspects of processing structure performance. Although a series of breakthroughs have been made in the physical properties of carbon nanotube fibers and many successful applications have been made, it is still necessary to reconsider the spinning process from the source.