Molecular Simulation of Strain Dependence of Vibrational Frequencies for Montmorillonite Clay and Analysis of Strain Transfer in a Polymer−Clay Nanocomposite

Abstract

Molecular dynamics simulations are used to determine the vibrational density of states for a model montmorillonite clay as well as the spectral shifts with applied strain for significant peaks in the 1000−1300 cm-1 range. Under uniaxial deformation with fixed lateral dimensions, the spectral shifts are found to be around −29 and −40 cm-1/% strain in the clay, with little dependence on direction of applied strain within the plane of the clay platelet. Using Eshelby's method, a strain transfer efficiency of 5.6% is predicted for the nanocomposite with 5 wt % exfoliated clay. This results in a predicted spectral shift of −1.6 to −2.2 cm-1/% macrostrain in the nanocomposite, in reasonable agreement with the experimental results of Loo and Gleason (Macromolecules 2003, 36, 2587).