Molecular dynamics simulation of the first stages of the cavitation process in amorphous polymers

The first stages of the cavitation process in amorphous polymers submitted to an hydrostatic deformation in the glassy state are studied with coarse grain molecular dynamics simulations for various intermolecular interactions strengths and flexible and semi-flexible chains. For strong intermolecular interactions, the cavitation process is highly localized and the holes have a marked spherical symmetry. The cavitation regions are more diffuse for weaker intermolecular interactions or when the chain stiffness is increased. The mean Voronoi polyhedra volume and the disorder inside the polymer increase until the stress peak observed below the glass transition. High mobility regions are present before the stress peak that may act as nucleation sites for the cavitation process. The localization of these high mobility zones is enhanced for strong intermolecular interactions or a low chain rigidity. Moreover, the velocity fluctuations are more marked in the vicinity of the holes. For strong intermolecular interactions, the holes are not randomly distributed throughout the system and the nucleation of cavities upon deformation occurs preferentially near the chain ends of the polymer.