Carbon nanotubes are a kind of super materials with great potential, and they are the ideal core basic materials for the construction of future super structures and carbon-based semiconductor devices. Assembling carbon nanotubes into macroscopic bodies (such as fibers, films, foams, etc.) is one of the important ways to realize the large-scale application of carbon nanotubes. Carbon nanotube fiber is a one-dimensional continuous assembly of carbon nanotubes, which can not only be used alone, but also can form a two-dimensional film or a three-dimensional braided structure by weaving, becoming the most concerned carbon nanotube macro body. In the past two decades, people have been devoted to the development of carbon nanotube fiber continuous spinning process, revealing the process-structure-performance relationship of carbon nanotube fiber, and developing the engineering application of carbon nanotube fiber. A large number of existing studies have shown that carbon nanotube fibers have very broad application prospects in structural and functional integrated composite materials, fibrous energy devices, artificial muscles, and lightweight conductive cables. Unfortunately, from nanoscale single carbon nanotubes to macroscale carbon nanotube fibers, the efficiency of carbon nanotubes in power, electricity, heat and other properties is less than 10%, which limits the carbon nanotube fibers. Engineering application. Understanding and clarifying the process-structure-performance relationship of carbon nanotube fibers is the key to further improving the performance of carbon nanotube fibers.
Li Qingwen, a researcher at the Suzhou Institute of Nanotechnology and Nanobionics, Chinese Academy of Sciences, has been conducting a lot of basic research and application development work in the field of carbon nanotube fibers since its establishment in 2007. Recently, the team was invited to write a review article (DOI: 10.1002 / adma. 201902028) in the journal Advanced Materials, systematically reviewing the work carried out by people on basic physical properties of carbon nanotube fibers in the past two decades, and The key to the future development of carbon nanotube fibers is prospected.
Looking back at the development process of carbon nanotube fibers, we can find that China has conducted carbon nanotube fiber research earlier in the world. In 2000, French scientists first reported the preparation of continuous fiber materials with a carbon nanotube content of more than 50% through the wet spinning process, which opened the prelude to the research of carbon nanotube fibers. In 2002, the team of Professor Dehai Wu from Tsinghua University and PM Ajayan, a professor at Rensselaer Polytechnic Institute, reported for the first time the use of floating chemical vapor deposition to prepare carbon nanotube bundles with a diameter of about 300 to 500 microns, with a length of 20 cm; in the same year, Tsinghua University professor Fan Shoushan ’s team first reported the method of preparing carbon nanotube fibers from carbon nanotube array drawing; in 2004, Chinese scientist Li Yali cooperated with Professor Alan Windle during his visit to Cambridge University in the United Kingdom to realize the floating catalytic chemical vapor deposition method Continuous production of carbon nanotube fibers. During this period, American scientists reported on the wet process for preparing pure carbon nanotube fibers. In 2018, a team of professor Wei Fei from Tsinghua University reported a bundle of centimeter-scale carbon nanotubes with an intensity of 80 GPa. In general, since scientists successfully assembled carbon nanotubes at the macro-scale fiber around 2000, the research of carbon nanotube fibers has risen rapidly, and has generally experienced three development stages in the development of 20 years: (1) carbon The exploration stage of the nanotube fiber spinning method-wet spinning based on the coagulation process, drawn spinning using a vertical array of carbon nanotubes and direct spinning based on the growth process pre-formed carbon nanotube gel have become the most important at present The preparation method; (2) The rapid development stage for the continuous continuous preparation of carbon nanotube fibers, the improvement of basic performance and the development of functional characteristics; (3) The current development of carbon nanotube fibers has entered the stage of tackling industrial applications, how to bite The hard bones require the joint efforts of scientific researchers and industry.
Based on different spinning methods, carbon nanotube fibers exhibit an extremely rich assembly structure. Compared with its microstructure, the orientation, tightness, and entanglement of carbon nanotubes in the fiber, the radial distribution of the fiber, and the surface morphology and other structural characteristics determine the macroscopic physical properties of the fiber. More importantly, on the basis of improving the fiber assembly structure, the effective control of the force, electricity, and heat transfer between the tubes is the key to improving the fiber performance and giving full play to the performance of a single nanotube.
In the review of the research progress, the authors separately elaborated the mechanical, electrical and thermal properties of carbon nanotube fibers. In terms of mechanical properties, significant improvements in fiber breaking strength and elastic modulus can be achieved through solvent densification, mechanical densification, stepwise drafting, introduction of polymer network structures into the fiber, and induced covalent connections between tubes. On the other hand, the extremely rich interface structure in the fiber brings a variety of energy dissipation processes, making carbon nanotube fibers (and films and composite materials) exhibit dynamic mechanical properties such as damping and creep that traditional carbon fibers do not , To achieve the combination of rigid and soft dual function. In addition, the fiber's yarn structure and unique flexibility show unique advantages in the fields of rotation drive, bioelectrode and so on.
Carbon nanotube fibers are also excellent "conductors". In terms of conductive properties, after widening the electron transition channel between the tubes by doping, the fiber is expected to exceed the limit of the metal conductor in terms of specific conductivity performance and show development advantages in the direction of lightweight wires; and through compounding with metals, based on carbon The rapid thermal conductivity of nanotubes can greatly improve the ultimate current-carrying capacity of composite conductors, and is expected to replace traditional metal conductors in the application of ultra-large currents in the future. In terms of thermal conductivity, due to the unique assembly characteristics, the thermal radiation on the fiber surface is particularly significant, resulting in a huge difference between the actual thermal conductivity and the actual thermal conductivity in the actual measurement, and the former quickly diverges as the sample size increases. To this end, in addition to optimizing the fiber structure to improve phonon transport between tubes, further development of test methods is also an important part of the research on the thermal conductivity of carbon nanotube fibers.
In this review, the authors introduced the theoretical research related to force, electricity, and thermal performance respectively, and pointed out that the basis for further improvement of fiber performance and industrialization in the future still lies in the deepening of the internal relationship between processing, structure and performance. understanding. Although there have been a series of breakthroughs in the physical properties of carbon nanotube fibers and multiple successes in device applications, it is still particularly necessary to re-recognize the fiber spinning process from the source.
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