Mechanical response of van der Waals and charge coupled carbon nanotubes

Abstract

This work investigates the mechanical response of single-walled carbon nanotubes (SWCNTs) coupled through van der Waals and electrostatic forces using molecular dynamic (MD) simulations and a continuum model. In MD simulations, the covalent bond interactions between the carbon atoms are modeled using three sets of ReaxFF potential parameters (Strachan et al 2003 Phys. Rev. Lett. 91 098301; Srinivasan et al 2015 J. Phys. Chem. A 119 571–80; Damirchi et al 2020 J. Phys. Chem. C 124 20488–97). The dynamic charges, dependent on the local environment, are calculated employing the charge equilibrium formalism within the ReaxFF. In the continuum model, the SWCNTs are modeled using the geometrically nonlinear Euler-Bernoulli beam theory. The Galerkin’s approach is used to discretize the equations of motion. An approximate model to account for the end charge concentration in the SWCNTs, calibrated from the MD data, is incorporated into the beam model. The pair of SWCNTs are prescribed with two sets of boundary conditions: Fixed–fixed and fixed–free. The pull-in voltages at which the two SWCNTs snap onto each other with fixed–fixed boundary conditions obtained from the MD simulations using the potential parameters of Strachan et al (2003 Phys. Rev. Lett. 91 098301), Srinivasan et al (2015 J. Phys. Chem. A 119 571–80) and Damirchi et al (2020 J. Phys. Chem. C 124 20488–97) agree within an error of ∼0.5% , ∼0.5% , and 7.2%, respectively, with those computed from the nonlinear beam theory. For fixed–free boundary conditions, the role of geometric nonlinearity is found to be insignificant. However, for this case, the concentrated charges play a significant role in determining the pull-in voltages. The post-pull-in response of the SWCNTs for both boundary conditions is investigated in detail through the MD simulations. The post-pull-in results presented here can be used as a benchmark for results obtained from continuum models in the future. Further, the proposed research helps design nano-resonators/tweezers/switches.