Microscopic Investigation of Shear in Multiwalled Nanotube Deformation

Abstract

The cylindrical geometry of nanotubes dictates a strong anisotropy of their physical properties. In practice, the difficulty in extracting individual components of the elastic tensor has limited the available information to only very partial and indirect experimental data. Here, the interlayer shear (sliding) modulus (C 44 ) of single multiwalled WS 2 nanotubes was studied by atomic force microscopy bending tests. The observed value of 2 GPa agrees well with the value of 4 GPa obtained for density functional tight binding calculations for 2H-MoS 2 . This value of the shear modulus represents a much higher degree of anisotropy than that obtained for carbon nanotubes and enables assignment of the mode of shear deformation.

In situ TEM measurements of the mechanical properties and behavior of WS2 nanotubes

“…Since no plastic deformation or failure can be observed in Figs. 1(a) (b), the estimated strain is compatible with the previous data [10,11]. Furthermore, the higher strain value that was evaluated for the nanotube when it was further deformed (Fig.…”

“…As for WS 2 nanotubes, the value obtained for their bending modulus is slightly higher compared to the Young's moduli determined by using other techniques as well as by DFTB calculations (150 170 GPa) [9,10,36]. Former bending tests of WS 2 nanotubes resulted in a nonlinear elastic behavior for large defl ections (as was demonstrated according to the force defl ection curves) [11]. The value of the Young's modulus calculated from the maximum deflection of these nanotubes was superfluous.…”

“…This behavior is unique to the defect-free nanotubes and do not characterize the bulk material, which is full with defects of different kinds [10]. Moreover, the sliding modulus between different walls of the WS 2 nanotubes (which was determined by bending tests), was found to be smaller (2 GPa) compared to that of bulk MoS 2 (19 GPa) [11]. It is believed that the (telescopic) sliding of the defectfree multiwall nanotubes is dictated by pure van der Walls interaction between the shells.…”

“…The differences can be attributed to the dissimilar nanotubes' length (rigidity) and the loading conditions. Former studies of WS 2 nanotubes both under postbuckling [10] and bending [11] showed a nonlinear elastic behavior. Presumably, this nonlinearity can be attributed to the kinks that tend to form in the tubular structure which was confi rmed by the in situ…”

“…It is believed that the (telescopic) sliding of the defectfree multiwall nanotubes is dictated by pure van der Walls interaction between the shells. Contrarily, the bulk material contains substantial amounts of defects, which pin the layers together, preventing thereby their almost free sliding [11].…”