Elastic Properties of a Single Lamella of Montmorillonite by Molecular Dynamics Simulation

Abstract

We present results for the elastic properties of a single lamella of montmorillonite consisting of two tetrahedral layers and the intervening octahedral layer. The calculations were performed using a force field with both bonded and nonbonded interatomic contributions and periodic boundary conditions in two dimensions, representing an infinite “nanoplate”. The elastic response of the atomically thin nanoplate was calculated from curves of force versus displacement obtained at slow rates of deformation. Bending stiffness was estimated independently from the onset of nonlinear deformation under compression. The atomistic results are explained in terms of a continuum model for thin plates. We obtain values for the in-plane elastic properties of 250−260 N/m for E1h and E2h, and 166 N/m for the in-plane shear response, G3h, where h is the thickness of the nanoplate. The effective mechanical thickness of the clay lamella is found to be 0.678 nm, comparable to the distance between the outermost layers of atoms on either surface of the atomically thin sheet (0.615 nm). A bending modulus of 1.25 × 10-17 Nm is obtained from the critical stress for nonlinear compression.