Evaluation of effect of annealing and diameter on tensile strength of carbon nanotube using ultrasonic cavitation induced fragmentation

抄録

Carbon nanotubes (CNTs) are thought to have higher tensile strengths than those of carbon fibers. However, it is difficult to measure the strength of CNTs because of their nano-scale dimensions. In addition, there is a large discrepancy between the ideal strength of CNT and the experimental results for CNTs alone. This is thought to be due to defects in the CNTs and residual catalyst in the CNTs, which degrade the mechanical properties of the CNTs. In this study, tensile strength was estimated using a method called ultrasonic cavitation induced fragmentation, which is different from conventional strength evaluation methods. Ultrasonic cavitation induced fragmentation is a simple way to cut carbon nanotubes in suspension. The lengths of fragmented carbon nanotubes are made shorter by iterating ultrasonication but approaches a critical aspect ratio. It is possible to evaluate the tensile strength of CNTs from the critical aspect ratio. In this study, the effects of annealing, which is known to improve the tensile strength crystallinity of CNTs by reducing defects and catalysts, and diameter, the reduction of which reduces defects and increases the ratio of load-bearing layers, on the tensile strength of CNTs are evaluated by using the ultrasonic cavitation induced fragmentation. The results showed that thinner CNTs were stronger, and annealing decreased the tensile strength of MWNTs. The latter implies that the increase in crystallinity does not always increase the tensile strength of MWNTs.