Tracking a glassy polymer on its energy landscape in the course of elastic deformation

Abstract

The response to deformation of a detailed computer model of glassy atactic polystyrene, represented as a collection of basins on its potential energy landscape, has been investigated. The volumetric behaviour of the polymer is calculated via ‘brute force’ molecular dynamics quenching simulations. Results are compared with corresponding estimates obtained by invoking the quasi-harmonic approximation (QHA) for a variety of temperatures below the glass temperature and with experimental data. The stress-controlled uniaxial deformations fall in the linear elastic regime and the resulting strains are calculated as ensemble averages of QHA estimates over 200 uncorrelated inherent structures of the potential energy landscape. The elastic constants (Young's modulus and Poisson ratio) and their temperature dependence are in very good agreement with experiments for glassy atactic polystyrene. Additionally, a classification of the deformed inherent structures in respect to the geometry and general shape of their energy minima is undertaken. A distortion of the potential energy basins upon mechanical deformation in the elastic regime is observed in all cases.