Recently, Professor Wei Fei from the Department of Chemical Engineering of Tsinghua University teamed up with Professor Li Xide from the Aerospace Institute of Tsinghua University to make a major breakthrough in the field of super-strong carbon nanotube fibers. For the first time in the world, the theoretical strength of single carbon nanotubes was reported. The bundle of carbon nanotubes has a tensile strength that exceeds all other fiber materials found so far. The related results were titled "Carbon Nanotube Bundles with Tensile Strength over 80 GPa" and published online on May 14th in the world's top academic journal "Natural Nanotechnology". Nature Nanotechnology).
Structure preparation and mechanical properties of ultra-long carbon nanotube bundles
a. schematic diagram of carbon nanotube tube bundle; b. structure of ultra-long carbon nanotube used; c. schematic diagram of preparation of ultra-long carbon nanotube tube bundle by gas flow focusing method; d. super long carbon nanotubes merge under focused gas flow Simulation diagram; ei. prepared ultra-long carbon nanotube tube bundle with a certain composition; jk. mechanical properties of carbon nanotube tube bundle prepared; l. ultra-long carbon nanotube tube bundle and other
The pursuit of the ultimate performance of materials has always been one of the important driving forces for the development of human society. The mechanical strength of a material is one of the many properties of a material that is highly valued by humans. NASA set up a "Strong Tether Challenge" in 2005 as a century challenge, hoping to find a specific strength (ie, unit mass strength) of up to 7.5 GPa/(g). /cm3) macro-strong fiber material. Unfortunately, it was not possible to achieve this goal until 2011. It is known that the specific strength of macroscopic materials is much lower than 7.5GPa/(g/cm3), such as 0.05~0.33GPa/(g/cm3) for steel wire rope and 0.5~3.5GPa/(g/cm3) for carbon fiber . The molecular fiber is 0.28~4.14 GPa/(g/cm3). In addition, super-strong fibers have extremely broad application prospects in other fields, such as high-performance sports equipment, body armor, large aircraft, large launch vehicles, and super buildings.
Carbon nanotubes are considered to be one of the strongest materials currently found, with Young's modulus up to 1 TPa and tensile strength up to 100 GPa (specific strength up to 62.5 GPa/(g/cm3)), exceeding T1000 carbon fiber. The strength is more than 10 times. Theoretical calculations show that carbon nanotubes are currently the only material that may help us realize the dream of space elevators. However, when a single carbon nanotube with excellent mechanical properties is prepared into a macroscopic material, its performance is often far lower than the theoretical value. For example, the reported carbon nanotube fibers have a strength of only 0.5 to 11.5 GPa (specific strength of 0.3 to 7 GPa/(g/cm3)), which is much lower than the theoretical strength of carbon nanotubes (>100 GPa). The main reason is that the carbon nanotubes forming the fibers have a short length, and the van der Waals force overlaps each other with the van der Waals force. Under the tensile force, the mutual slip occurs easily, and the intrinsic high strength of the carbon nanotubes cannot be fully utilized. In addition, structural defects and disordered orientations in the carbon nanotubes cause a decrease in fiber strength.
In contrast, ultralong carbon nanotubes have a centimeter or even decimeter length and have a perfect structure, have a uniform orientation and mechanical properties close to the theoretical limit, and have great advantages in the preparation of super-strong fibers. By using the in-situ gas stream focusing method, the research team controlled the preparation of centimeter-scale continuous ultra-long carbon nanotube bundles with certain composition, perfect structure and parallel arrangement, which cleverly avoided the above-mentioned limiting factors. The effects of composition and structure on the mechanical properties of ultra-long carbon nanotube bundles were quantitatively analyzed by preparing ultra-long carbon nanotube bundles containing different numbers of units, and a definite physical/mathematical model was established. It is found that the initial stress distribution of the carbon nanotubes in the tube bundle is not uniform, so that the carbon nanotubes in the tube bundle cannot be uniformly and uniformly stressed, which leads to a decrease in the overall strength, that is, the "daniel effect". Based on this, the research team proposed a "synchronous relaxation" strategy, which releases the initial stress of the carbon nanotubes in the tube bundle by nanomanipulation, so that it is in a narrow distribution range, thereby stretching the tensile strength of the carbon nanotube bundle. Increase to above 80 GPa, close to the tensile strength of a single carbon nanotube. The mathematical model calculation results show that for a tube bundle formed by an infinite number of such ultra-long carbon nanotubes, the tensile strength can be maintained under the premise of ensuring continuous length, perfect structure, uniform orientation and uniform initial stress distribution. Approach single strength.
This work reveals the bright future of ultra-long carbon nanotubes for the manufacture of super-strong fibers, while pointing out the direction and method for the development of new super-strong fibers. The reviewer commented: "The author of the paper has made a landmark breakthrough in the world, for the first time in the world to report carbon nanotube bundles close to the strength of single carbon nanotubes. This work has extremely far-reaching influence, it Undoubtedly will cause widespread concern around the world." The research work was funded by the National Natural Science Foundation of China and the National Major Research and Development Program.
The first author of the thesis is Bai Yunxiang, a doctoral student of the Department of Chemical Engineering of Tsinghua University, Zhang Rufan, a young teacher of the Department of Chemical Engineering, and Ye Hao, a Ph.D. graduate of the Department of Mechanics of the School of Aerospace Engineering. The co-authors of the paper are Prof. Wei Fei from the Department of Chemical Engineering of Tsinghua University, Dr. Zhang Rufan and Professor Li Xide from the School of Aerospace.
In the past ten years, Weifei team has carried out a lot of research on the growth mechanism, structure controllability, performance characterization and application exploration of ultra-long carbon nanotubes, and has made a series of important breakthroughs. The team has produced a single carbon nanotube with a length of more than half a meter and has a perfect structure and excellent performance, setting a world record. In addition, the team first discovered the ultra-lubrication phenomenon between the macro-length carbon nanotube layers, and realized the optical visualization and controllable manipulation of the single carbon nanotubes at the macroscopic scale. The above results have been published in Nature Nanotechnology, "Nature Communications", "Chemical Society Reviews", "Accounts of Chemical Research", "Advanced Functional Materials". (Advanced Materials) In the international journals such as ACS Nano "Nano Letters", it has aroused widespread concern in the academic community and laid the foundation for the development of super-long carbon nanotubes for the preparation of super-strong fibers. . The team of Professor Li Xide of the School of Aerospace and Aeronautics has been conducting research in the field of micro-nano mechanics. He has carried out a lot of research work on the measurement and characterization of mechanical properties of micro-scale materials. The relevant research results are published in Nature Communication and Physics. International Journals such as Physical Review Letters, Scientific Reports, Nanotechnology, and Applied Physics Letters.
Nature Nanotechnology, a monthly magazine of the Nature Publishing Group, had an impact factor of 38.99 in 2017 and ranked first in nanoscience and nanotechnology journals.
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