Revealing the nature of long-range interfacial effect on polymer dynamics under confinement

Interfaces play an important role in modifying the dynamics of polymers confined to the nanoscale. Proximity to substrate interface substantially slowed polymer dynamics, and the dynamics slowdown can be propagated over tens or even hundreds of nanometers into film interior, exhibiting a long-range interfacial effect. The nature of this surprisingly long-range effect remains unsolved. The central question is how the suppressed interfacial dynamics can be transmitted over such a long distance. In our investigations, we considered the essential role of formation of an irreversible adsorption layer with sluggish molecular dynamics atop the substrate surface. We exploited our ability to tune local conformation and molecular packing of chains in the adsorbed layers, together with the thin-film dewetting experiment, to show that there could be an interphase in between the adsorbed layer and polymer matrix due to the differences in chain conformations in the distinct regions (i.e., conformational asymmetry); the chains' topological interactions (e.g., chain interpenetration, entanglement and proximity to each other) in interphase region are crucial to the propagation of suppressed interfacial dynamics. The topological interactions increase motional coupling of chains and facilitate the propagation of suppressed dynamics originating at the interface. The results highlight the ability to manipulate interfacial effects and confined polymer mobility by conformation and packing state of chain in adsorbed nanolayers, as well as the importance of topological interactions between adsorbed chains and free chains in matrix.