(549d) Molecular Simulations of Confined Glass-Forming Polymers

For many technological applications ranging from semiconductor manufacturing to flexible displays, the properties of glass-forming materials when they are confined to  nanoscopic dimensions are of critical importance. For example, common semiconductor manufacturing techniques rely on the mechanical integrity of amorphous polymer nanostructures. Experiments over the past several years have demonstrated that many of the properties of polymer glasses (e.g., the glass transition temperature, Tg, and the elastic constants) can change significantly and in unintuitive ways when confined to dimensions below approximately 100 nm. These confinement effects depend strongly on the detailed polymer chemistry. In this talk, I will describe our recent work using molecular simulations to study the effects of nanoscale confinement on both the dynamic and mechanical properties of a series of coarse-grained polymer models. Our coarse-grained models systematically explore the effects of polymer chemistry by gradually changing the polymer backbone stiffness and analyzing the strengths of the confinement effects. We characterize confinement effects through a detailed analysis of the local dynamics and local mechanical properties for each polymer confined to free-standing thin films, and the results are compared to bulk simulations. All of our polymer chain lengths are above the bulk entanglement chain length, and we explore how the chain dynamics and the entanglement network are affected by nanoscale confinement. The results of these simulations provide significant new insights on the relationship between polymer chemistry and the strength of the effects of nanoscale confinement.