How Does Monomer Structure Affect the Interfacial Dynamics of Supported Ultrathin Polymer Films?

We utilize chemically specific but coarse-grained models of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) to explore the influence of monomer architecture on the dynamics of supported thin polymer films based on molecular dynamics simulations. We contrast differences in the molecular packing and mobility gradients in these materials near the substrate and “free” interface regions. The dynamics near the substrate are more sensitive to monomer structure, and are enhanced with increasing polymer–substrate interaction strength, ε. PMMA is relatively stiff compared to PEO and has a side group, and the dynamics of PMMA near the substrate are slowed significantly in comparison. Substrate interactions lead to a notable difference in local fragility due to a higher cohesive interaction strength of PMMA in this region. Our data also reveal the inadequacy of the these coarse-grained models to reproduce the experimentally known differences in the fragility. However, this technical shortcoming is not expected to alter our qualitative conclusions regarding the comparative effect of substrate interactions on relatively flexible polymers such as PEO versus a relatively stiff polymer such as PMMA.