Molecular Dynamics Simulation of Cavitation in Network Polymer Gels*

Cavitation, the sudden formation and expansion of a void, causes both reversible and irreversible changes in soft materials. While extensively studied in simple fluids, there is little insight into cavitation in soft solids which contain both structural components and a fluid phase. Crosslinked polymer networks swollen in solvent, such as hydrogels, have gained growing attention due to properties that mimic natural materials and soft tissues. As network structure is intimately related to material properties, it is important to gain insight into the dynamic behavior of the network during mechanical deformation. Coarse-grained molecular dynamics is used to study the response of swollen polymer networks to isotropic dilation, and we examine the connection between local structure and cavity formation in gels. We use tensile deformation to induce cavitation in both model perfect diamond networks and defect-containing networks as a function of the polymer concentration and strand length. We find that the local structure is highly correlated with cavity formation, and surprisingly we find that the cavities tend to form in specific locations in the network and are not randomly distributed. Finally, we conclude by characterizing the structural features that promote cavitation.