Abstract

Transparent amorphous polymers such as polycarbonate (PC) have been widely used in structural applications and have been a topic of theoretical, experimental and computational study for several decades. Recently, with the rapidly increasing capacity of numerical computing, molecular dynamics (MD) simulation has become a powerful tool for the further study of material behavior in full atomistic detail. In most cases molecular level motions are key contributors to the observed macroscopic response, but are not easily obtained experimentally. MD simulation can be used to provide a picture of these motions, and thus help elucidate the underpinning molecular mechanisms during deformation and can, in some cases, provide insight into how a material may behave under complex loading conditions. A relatively large all-atom MD system (containing 198365 atoms) of PC with a realistic molecular distribution (polydispersity) was built and studied. The MD system was constructed using the PCFF force field, which was initially developed for PC. The model was validated and evaluated by comparing the stress-strain responses with a large number of existing experimental results under various loading conditions. To capture and analyze the molecular motions, the molecular deformation gradient (using the “MinD method”) was calculated for the individual molecules and compared to the bulk deformation. The difference between volumetric, principal, and deviatoric molecular and bulk deformations was used to illustrate the molecular motions during the different stages of deformation (e.g., elastic loading, plastic flow, and hardening). This work employs our newly developed tools to quantify and characterize the molecular mechanisms underlying the response of PC to various loadings. The procedures can easily be adapted to study other polymers and systems with different microstructures.

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