Among the available nanomaterials, single-walled carbon nanotubes (SWCNTs) have specifically attracted significant research attention owing to their lightweight and excellent mechanical and optical properties. With the establishment of the technology for providing of the SWCNTs for water through wrapping in single-stranded DNA (ssDNA), their potential applications have tremendously increased. However, to fully realize these applications, it is vital to understand the macroscopic behaviors and vibration characteristics of SWCNTs that would help in eliminating unwanted defects like fatigue fracturing. Despite numerous studies about the mechanical and vibration characteristics of single-walled carbon nanotubes, these characteristics have not been fully explored in ssDNA and SWCNT composites.
To this note, Daisuke Miyashiro (currently ESTECH CORP.) and Professor Kazuo Umemura from Tokyo University of Sciences together with Dr. Hisao Taira from the Hokkaido University of Education developed a new approach for analyzing the vibration characteristics of SWCNTs wrapped with ssDNA based on finite element method (FEM). In particular, they investigated the influence of their interactions in water and vacuum conditions. The work is currently published in the research journal, Composites Part B: Engineering.
With the innovative and advanced FEM, it was possible to obtain results with high accuracy in a wide frequency range. The SWCNTs with a length of 150nm model was calculated from the 1st-bending mode of 0.98GHz to the radial breathing mode (RBM) of 10.2THz under free boundary conditions. The feasibility of the method in practical applications was validated by designing an appropriate length of single-walled carbon nanotubes concerning the absorption stiffness between the single-stranded DNA and single-walled carbon nanotubes. Also, they simulated its ability to eliminate mechanical vibrations leading to instability, fatigue, and destruction.
The authors successfully obtained the vibration modes and conditions for coupling with the ssDNA and the 1st-bending mode of SWCNT composites in both water and vacuum. Additionally, regarding the analysis accuracy, the natural frequency in bending vibration of the SWCNTs was observed to be consistent with the Bernoulli-Euler beam theory. Similarly, the natural frequency of SWCNT in the RBM was also consistent with the experimental relationship between the obtained wavenumber of RBM and dimeters of SWCNTs.
The FEM achieved highly accurate results over a wide frequency range from GHz to THz. It was capable of simulating typical modes like bending, twisting, and radial breathing mode vibration in the radial direction. Consequently, the obtained simulation results clarified the various conditions necessary for coupling with the 1st-bending mode of the ssDNA and SWCNT composites. This significantly contributed to the prediction of the optimal lengths, absorption stiffness and diameters of the composites. It is also applicable for more complex composites. By studying the interaction between the ssDNA and SWCNTs, it was possible to suppress the vibration amplitude thus preventing structural damage.
In summary, the finite element study presents a novel approach for understanding the behavior of microscopic vibration. According to Miyashiro the lead author in a statement to Advances in Engineering, the approach will significantly advance the design of optimal ssDNA and SWCNT composite according to the desired application.
Miyashiro, D., Taira, H., & Umemura, K. (2019). Vibration analysis of single-stranded DNA-wrapped single-walled carbon nanotubes using finite element method. Composites Part B: Engineering, 173, 106896.