Spatial variations in dynamic heterogeneity in polymer thin films

Polymers in the nanoscale vicinity of interfaces can exhibit immense alterations in relaxation dynamics and glass formation behavior. These alterations take the form of large spatially-organized gradients in relaxation dynamics near an interface. At the same time, bulk glass-forming liquids such as polymers exhibit a substantial degree of spatial dynamic heterogeneity in the form of a distribution of local relaxation times, albeit without the degree of static spatial organization inherent to interfacial gradients in dynamics. Here, we describe results of molecular dynamics simulations probing the interplay of these effects. How does the presence of an interfacial dynamical gradient alter the dynamic heterogeneity present in bulk? How does the presence of heterogeneity in turn alter near-interface dynamics in and out of equilibrium? How is the anisotropy of dynamics altered near interfaces? By employing simulations in the isoconfigurational ensemble, here we provide insight into the answers to these questions.