Effects of nanotube size and roof-layer coating on viscoelastic properties of hybrid diamond-like carbon and carbon nanotube composites

Hybrid carbon nanobuffers are developed by exploiting the ultra-hardness and wear-resistant properties of diamond-like carbon (DLC) coatings and the inherent viscoelasticity properties of vertically aligned carbon nanotubes (VACNTs). The viscoelastic properties of carbon nanobuffers incorporating thin-walled and thick-walled CNTs, respectively, are characterized by means of nanoindentation dynamic mechanical analysis tests. It is shown that the thin-walled nanobuffer has a better damping performance than the thick-walled nanobuffer due to its buckling-driven friction and post-buckling behaviors; particularly under large displacements. In addition, it is shown that under large indenter displacements, the VACNT arrays with DLC coatings display the improved stress distributions and enhanced strain energy dissipation performances due to the load transfer on the top of VACNTs. Molecular dynamics (MD) simulations are performed to investigate the roof-layer effect on damping behavior and structural deformation of the coated and uncoated VACNTs under nanoindentation. The results confirm that the VACNT with a DLC coating exhibits the significantly damping characterizations than the non-coated VACNT. Overall, the results presented in this study reveal the potential for tuning the damping performance of CNT-based nanobuffers through a careful control of the CNT size.