Molecular simulation of strain dependence of vibrational frequencies for montmorillonite clay and analysis of strain transfer in a polymer-clay nanocomposite

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).