Computational studies on interparticle forces between nanoellipsoids

Abstract

The adapted continuum models pertinent to ellipsoidal microparticles do not generally hold at the nanoscale due to the approximations apart from the surface effects and the neglect of atomic discrete structure. The governing equation of describing the interactions, non-contact forces in particular, between ellipsoidal nanoparticles is lacking. In this work, the interaction forces including van der Waals (vdW) attraction, Born repulsion and mechanical contact forces between nanoellipsoids are studied by molecular dynamics (MD) simulation and compared with those predicted by the adapted continuum models (Hamaker or Hertz model). The results show that the interaction forces between ellipsoidal nanoparticles are complicated and the ratios of interaction forces obtained from the MD simulations to those from the adapted Hamaker equations are dependent on surface separation, particle size, aspect ratio and configurations. Under different configurations, two formulas have been proposed for vdW attraction and Born repulsion forces. In particular, under parallel configuration, both the vdW attraction and Born repulsion forces between nanoellipsoids show an obvious periodic variation stemming from the step-like atomic structure and can be described by a second-order Fourier expansion and correspondingly another two relatively more accurate formulas are proposed for vdW attraction and Born repulsion forces. Moreover, the mechanical contact force between ellipsoidal nanoparticles at low compression still can be described by the Hertz model. This work can provide quantitative insights into interaction forces between nano-ellipsoids and should be useful in the applications where ellipsoidal particles are involved, such as self-assembly by virtue of inter-particle or external forces.