The Role of Position-Dependent Decoupling of Translational and Reorientational Dynamics in Thin Film Metrological ‘Discrepancies’

Many of the central challenges in the study of glass formation and dynamics in nanoconfined systems center around apparent inconsistencies between results from distinct metrological simulations and from simulation. Key examples include frequently weaker effects as observed by dielectric spectroscopy than by pseudothermodynamic methods, an extrapolated disappearance of nanoconfinement effects at temperatures modestly above Tg that is not typically reported in simulation, and a seeming nonuniversality regarding the presence of smooth surface dynamic gradients vs distinct surface relaxation processes. Here we employ molecular dynamics simulations to examine these discrepancies within the context of decoupling between translational and reorientational dynamics near the interface. Results suggest that differential interfacial effects on translational and reorientational dynamics over a range of molecular stiffness play an important and largely unrecognized role in yielding differential measures of nanoconfinement by different methods.