(695g) Confinement and Substrate Effects on the Nanoscale Interfacial Rheology of Glass-Forming Fluids

Microscopic interactions at polymer interfaces significantly influence material performance in numerous nanostructured polymeric materials. At nanoscale interfaces, polymers exhibit altered mechanical and dynamical behaviors due to confinement effects and interface interactions. Despite significant interest in these materials, there is an incomplete understanding of how modified molecular mobility at interfaces impacts rheological properties. We investigate the nanoscale interfacial rheology of glass-forming fluids, emphasizing the interplay between interface effects on glass transition temperature (T_g) gradients and polymer chain connectivity. We report on molecular dynamics simulations probing the question of how dynamical gradients in T_g and segmental relaxation time near interfaces translate into gradients in chain relaxation and viscosity. We find that polymer chain connectivity substantially modulates dynamical gradients at a whole-chain-motion level, with chain motion exhibiting gradient behavior distinct from that of segmental dynamics. We discuss potential updates to classical theories of polymer chain dynamics to account for behavior in these large, spatially organized dynamical gradients. These insights are relevant to a range of technologies from thin film processing to nanocomposite mechanics.